My Mechanic and I are trying to figure why my MPG is so bad.
Exclusive in town I'll get 9-12 mpg.
Exclusive highway I'll get about 21 mpg.
Combination is between 10-14?

New plugs, wires, pertronic and carbs and timing are adjusted. My British Mechanic doesn't think it's the tune up.
He's sat next to me while I drive the car and says my driving is fine. I don't push the car. I don't jack rabbit start. Freeway speed is about 70 in overdrive.
He doesn't understand why the in town is so low if I get 21 on the highway.

Can my in town shifting, driving be so bad that it really is my fault?

Funny that Greg offered to take my car for a while, for I actually told my mechanic that I'm going to fill the tank and let him drive it and see what he gets.

I'm happy my car drives like a dream and I've worked out all the bugs....except the mpg one. When push comes to shove, I'll take bad mpg over constant running problems and being stranded on the side of the road.

9 miles per gallon!

Any ideas at all guys?

Cheers,
Roger

I'd be worried about the mixture, since it sounds like you've checked the points. Have you tried warming it up then quickly turning it off and checking a plug? I bet timing can affect it, too.

Yep I tried to tell you so.--Keoke--

I'm willing to check anything again.
I do not have points, I have a Pertronic set up.

I will warm it up, turn it off, then check...a plug? Which plug and what am I looking for?

I'm looking for something to offer my mechanic to check out.

As previously said, he has set the timing, new plugs, wires, cap, roter, pertronics, and tuned both carbs. He also did a drop test with the carb bell housing. He rebuilt both carbs, so they have new parts. Starts and shuts off with no run on. Car runs great.

What is it you tried to tell me Keoke?
Roger

How long has this problem been going on? I recall you had an issue with the carbs a while ago, wasn't it a sticking piston? Are you sure the floats are closing properly? A small vacuum leak? I'm using a shotgun here.

Hi Greg,

Thanks for shotgunning this.
My poor mpg thing has been going on for about a year now.
The carbs were totally rebuilt and the drop test done. The only time I have encountered the float bowls sticking (twice only)is when I could not start the car. I gave it a tap and then it unstuck. We've checked for a vacuum leak too, no leak.

Here's what my mechanic throws out. I don't know where the problem is. You car idles between 7-10. You're getting 21 on the highway.

The tranny has been rebuilt within the year and the more I drive, it's getting quieter and shifting smoother. He threw out to check what the rear end ratio was, which was my previous post question.

I'd like to find out what is going on. Maybe my driving style really is the source.
Roger

roger, do you know if your fuel gauge is reading correctly?, are you using the "stick" check against what your fuel gauge is reading?, im asking just how are you checking your fuel level?

Pull a plug from the first three cylinders and one form the last three. They should look alike in color. They should be a light tan. YOU should check the gap on the plugs (which ones are you using?) There is something wrong with that millage. How long are you warming up for? How fast are you idling? Who's gas are you using and which grade? You could also try putting the points back in and check the millage again. I get 15 to 18 in town and 21+ on the highway.

Hi Anthony,
I am not using the stick method. I fill the tank, clear the odometer, refill the tank and divide the miles into the gallons.

I will go buy a stick and mark it. So next time I will make sure the gas level is the same on the stick when I do the gallons vs odometer.

Thank you,
Roger

tahoe healey, im in total agreement with what you and others are suggesting, we all know how accurate our healey fuel gauges fungtion, im just wondering how he judged the amount of fuel he says hes burning, i.e did he just drive the car until it ran out of gas, or did he just fill the tank and think his gauge reading of 1/8 tank remaining was correct, does he have excessive smoke exiting the exhaust at idle?, i think id check the easy stuff first then go on to changing back to points etc, etc.

Guys I don't think the fuel gauge is the issue. I don't use it for MPG.

I fill the petrol tank, set the odometer to 000000
I refill the tank and divide the number of miles driven into the number of gallons of gas used.

No excessive smoke at idle.

Why do you think using points would provide better mileage?
I was under the impression, electronic was better and more reliable.

Roger

A thought: can you hear the fuel pump at idle? If so, it should be clicking no more than every 2-3 seconds. Faster than that and you might have a fuel leak somewhere. If you have a stock radio, tune between stations and you might be able to hear the pump firing on your radio.

Your engine when it is idling is operating in its most inefficient mode.
Yous for some reason is operating considerably below the norm.

This is to say it consumes too much fuel when you are driving in town and the engine idles at stops.
I am not sure how this is happening if your at speed freeway mileage is about correct.
If you have a yard stick you can check the fuel consumption in both modes. Keoke

This is just a theory. One of your carb floats might be sticking or perhaps even has a small leak and is partially submerged. When driving at higher speed (highway driving) the demaand for fuel is greater and the fuel is going into the carbs as needed. However, when you are driving slower or idleing and the demand would normally be less from the engine, the sticking or submerged float just dumps the excess gas out the overflow, causing the miles per gallon to decrease more than normal. OK, just a theory. I only suggest this as I have had experience from brand new floats that are not always reliable.

Shorn, thanks! I will look into that.
Really guys, I'm open to all theories. Keep them coming. I'd love to find the problem.
Cheers,
Roger

Could be a sticking carb piston that won't rise properly. Check the centering of the jets, make sure the suction chambers are clean on the inside. Also check if a needle is not bent and if it's fitted flush with the piston.

I used to drive my brother's MGA (I was 17), and would drive way too far, so turned back the odometer and drove a whole lot more to get it just above where it was....he caught me with MPG....think he was getting 3mpg during my drives???

Is the odometer working correctly???? Take it on the freeway and use the miliage markers to check the accuracy.

Pete

I'm wondering what impact the spark plug gap may have.
I have a pertronics, Lucas sports coil and my plugs are Champion RN12YC.
I don't know if David Nock set the gap to .025 which I think is correct for the standard coil. My other Mechanic told me today they should be set at .035 for the Lucas coil.

I just bought some new plugs and gaped them .035

Any thoughts on this?
Roger

That might make a difference, but not enough of what you're looking for.

Are you sure the car isn't running excessively rich? Here is a chart that can help you check the condition of the plugs after you've recently turned the car off: http://www.verrill.com/moto/sellingguide/sparkplugs/plugcolorchart.htm

Well, this thread has now got me calculating my mileage for the first time. I just filled up and drive mostly city miles, so I am anxious to find out.

It is too bad you did not post this a week or so earlier Roger, since we could have had someone look into the gubberment program that might have given you up to $4500 for that gas guzzling clunker of yours! Just think, you could be cruisin' in a brand new Prius!

I do not have any other suggestions other than make sure you use an electronic calculator to figure mpg. Long division is trickier than you think.

Hey Shorn,
Per you're idea, here's what I just did. I zip tied a bottle to the frame and ran both over flow tubes into it. The bottle will capture what, if any, gas over flows.

Thanks,
Roger

Tom,
I certainly appreciate your sense of humor. I am so the gas clunker. I pick Prius' out of my Healey grill! Long division, what's that? Is that what my parents use to say to us kids, that's new math, ask your father/mother.

Cheers,
PS. lie to me and tell my you got 8 mpg.

I showed the plugs to my local mechanic Steve today and he said they look good. Not sure what David Nock gaped them at, being he did the last tune up. Maybe .025?
Here's photos, starting with plugs 4,3,2,1

It would appear the my plugs 4 and 2 look like carbon fouled?

Plugs 6 and 5

Which year/model Healey do you have?I have an idea about your problem,need to know which motor.....And it is not your driving style,Roger, or the plugs......Wheelwright

64 BJ8.

Your plugs look normal, even lean (except for #2 and #4). Looks like #1 has some damage to the side electrode--possibly from detonation--and should be replaced.

Did you try monitoring your pump cadence like I suggested? There's a possibility you have a leak, which is more severe at idle when the needle valves stay mostly closed and less severe at speed when you're using more fuel and there might be overall less pressure in the system.

Changing your plug gaps won't help, and might induce missing--even crossfiring--as the higher voltage spark seeks a path to ground with less resistance. Stock Healey ignitions aren't designed to handle ultra-high secondary voltage.

Hi Bob,
My mechanic said the same thing you did, normal/lean.
I have looked for leaks, none, and the cadence is consistant.
Mechanic says to gap the plugs at .035 because of the sports coil output. You don't agree?

Not sure what you mean by "sports coil output." If your mechanic thinks your coil has a higher constant output and you need to gap the plugs wider to use it you need a different mechanic. A coil is essentially a 'step-up transformer;' i.e. it steps up the primary voltage by a factor determined by the number of secondary windings divided by the number of primary windings. The greater that ratio the greater the maximum potential output voltage of the coil. However, as soon as the secondary voltage has risen sufficiently for a spark to jump the plug gap--or find another path to ground--the coil will discharge its energy and the voltage will rise no higher. IOW, a stock coil and a 'sports' coil will fire at the same voltage with the same plug gap (hence, there is no advantage to a 'sports' coil in normal usage). If you increase the plug gap enough, however, at some point the stock coil will not produce sufficient voltage to jump the gap and you'll have a miss, whereas the 'sports' coil will still fire.

You'd think that increasing the secondary voltage would be a good thing, and for high-compression and lean-running engines that's true, BUT the secondary ignition system has to be designed to handle the increased energy, else the spark will take the easiest path to ground, which may be down the side of the rotor or cap, or even across the plug wires (aka 'crossfiring'). The Healey ignition, being of 1950s design, may not be capable of handling increased secondary voltage, as would be created with a larger plug gap. You'll likely get missing and/or crossfiring, if not right away then eventually as the greater spark energy cuts its own path to ground. At any rate, your poor mileage isn't due to ignition unless your engine is missing (a lot--you'd know it).

Guys

I am not quite sure what all the fuss is about, I have not exactly worked out the performance on the current car a BJ7 but when I had a 100/6, 34 Years ago, the engine was rebuilt by John Chatham and I was recording 13 around town and 23 on a run. Now I realize that you are down a bit on this but you are not a million miles away from it.
I think some one has done a survey on the subject on this forum some time ago.

I can say that with the BJ7 I was unwittingly recording much better figures than this but the top speed was 70 MPH, finally found the cause of the problem - running on one Carb. Once the problem was sorted, speed went up and MPG dropped drastically to match.

Bob

Hi Bob Spidell,
Thank you for taking the time to explain.
I rely on my mechanic to keep my car running it's best and to keep me from sitting on the side of the road waiting for the tow truck.

The reason I have the gold toned Lucas sports coil is because the Pertronics runs better with that then the stock silver Lucas coil. I was told because I am running the pertronics and the Lucas sports coil, then I should try setting the gap to .035 See how the car runs then we'll take a look at the plugs and see how they look.

I don't think this will impact my mpg.
Just following recommendations that some parts work better with other parts when set up a certain way. (Pertronics required the Lucas sports coil)

Cheers,
Roger

Hi Bob,
The fuss is about why such a low figure. Does it mean something needs adjusting or is there a leak or some problem I should be aware of? Or is it simply my driving style. (Which by the way is very conservative, no jack rabbit starts)
Cheers,
Roger

Well take the plugs on out to 0.040" not an Inch more and see if the low end mileage improves a bit.

Certainly you need not have any qualms about doing this because:

A good original Lucas secondary electrical system is quite capable of handling the 40KV output from the sport coil and that puts a whole lot more fire in the hole, which is what it's all about I have been told.--Keoke

Thanks Keoke,
Always good to see you've taken interest in my posts.

Hi Bob,
That is not how I understand the process. The coil doesn't discharge when it reaches any particular voltage. It discharges when the points open, causing a drop in voltage in the primary wiring of the coil. This change causes the secondary field to collapse-causing the high voltage discharge.


The plug gap doesn't create a higher voltage, it creates a higher resistance. Using a higher voltage coil can overcome that resistance and jump a larger gap. This can create a larger flame kernel for a better and more complete burn of the fuel mixture.

Greg,

You are correct, of course. I was thinking the plug would fire at a lower voltage with a smaller gap--which it will--but the spark voltage is determined by the strength of the collapsing field. Found this: http://www.custom-car.us/ignition/spark-plug/gap.aspx

Still not convinced a stock Healey ignition can handle uber voltage. I've had trouble with arcing down rotors and over distributor caps with a stock coil. Of course, some of the parts were aftermarket and that could be the problem (I won't use anything but Lucas caps any more).

The mfg should not matter. They should be gaped at .025 plus or minus .001. Checking the color of the plugs will tell you if you are running one carb richer that the other. Also listen to the exhaust for even soft tones.These are easy things to do before spending money with your mechanics.

Hey Rich,
Here's where the discussion has now turned to.
.025 for the Lucas regular coil?
.035 for a Lucas sports coil?

I need the Lucas sports coil for the Pertronix, that's a given.

By the way guys, I just filled the tank and I averaged 12 mpg (town and freeway driving) (points at .025).
Let's see what I get with a set of new plugs at .035

Cheers,
Roger

Your problem is probably related to cheap aftermarket replacement parts: Caps,Rotors and secondary wires.An original Lucas system is quite capable of living with the higher output voltage provided by a sport coil coupled with a Pertronix.

Them crappy parts aren't unique to our Healeys. I bought a set of plug wires for my Ford Ranger and they were arcing to the engine block within 2 weeks. What a pain to change too. The Healey is a dream in comparison.

I'm gonna side with Roger's mechanic on the .035 gaping. From the Pertronix website in regards to the Ignitor.


And for their Flame Thrower coil ( I couldn't find anything for Lucas, but they are both 40K)

All these upgrades are cumulative, so adding .005 for each HP component shouldn't be a problem.


IIRC the Holy Grail of flame propagation is a .070" gap, not particularly easy to get.

Not to argue, drivers handbook says .014-.016 pt gap& .025 plug gap.I've used either Lucas Sport coil or Bosch blue coils for years. Always gaped my pts. at .015 & plugs( usually NGK BP6es) at .025. On normally aspirated engines I've never gone beyond factory spec. On forced induction(turbo or supercharged) We usually decreased gaps to prevent flame blowing out-.030-.032. On very high-compression engines sometimes gap is decreased. Healey's aren't either of the above.As long as dizzy bushing is good pts aren't much of a problem, don't forget dist. cam lube. cheers Genos2

Roger, I don't think anyone has asked but what are idling at? The black plugs are not normal (2 and 4). I'd ask your mechanic why. Black is either oil if it is slick (bad rings)or too rich if black powder looking. Check that all gaps are the same.
I did not read that you have a non standard coil. I'd start going back to standard things to test what may have changed your MPG.

Hi Genos,
Sure, the gap for the points shouldn't change with a different coil. They are still working at 12 volts regardless of what coil is used. The stock spark gap will work, but a bigger gap (within reason) will work better when used with the parts mentioned in this thread.


Apples to oranges, my low performance truck is gapped @ .045" from the factory.

Richard, it idles between 7-10 depending on who knows what...how far I've been driving, day, temp, what shirt I'm wearing.

Mechanic looked at all the plugs and says, nothing to be concerned with, normal range. The back is dusty not oily. I did not gap the plugs in the photos and maybe those two were off. I now have new plugs installed which I gaped at .035.

I've always had this mileage issue. Even when I had point and the standard silver Lucas coil. I've always averaged 9-13 mpg, highway/town. Yesterdays fill up was 12mpg.

Thank you for your input Rich.

Cheers,
Roger

I've been talking to some other Brit Mechanics and one said that I may have the wrong needle, correct needle but worn, not set right etc. So I talked to my mechanic about the carb rebuild he did. He replaced the needles he tells me.

I replaced the gas filter yesterday. It is placed right after the fuel pump. It was not leaking by way. I change it every year. I checked for leaks after installing the new one. No leaks anywhere down the line right up to the carbs. I now have a bottle strapped to my frame that the two run off tubes from the float bowls now go into. The bottle will capture any gas and let me know if that could be the problem area.

I just can't seem to get a handle on this 9-12 mpg thing.

Gotta admit, this problem has piqued my interest--and others' too, obviously--so I'm gonna keep throwing things out there (as soon as I wipe the egg off my face for the 'gap gaffe').

Have you checked compression? If you had very high compression--say, over 175psi/cyl--you may have to run very rich to prevent detonation ('knocking'). There may be valve and/or ignition timing issues that could affect mileage, but I'll defer to others on those.

Also, I wonder why your idle is so inconsistent--my idle moves between 600 and 800rpm, but it's consistent depending on a few variables (air temp/density, engine temp, clutch in/out, etc.).

On a side note, last time I checked my plugs they looked a lot like yours. A couple, actually, are almost too clean; i.e. white, with no deposits. A couple had the brownish deposits like your #2 and #4, and the other two had the greyish deposits you'd expect from a good mixture of unleaded gas. I don't expect a carburetted car to have perfect mixture distribution, but the too-clean plugs have me baffled. I wonder if different fuel additives can cause different-colored deposits? Ideas, anyone?

Here is a wild idea. Are you sure you have the stock cam? Both of those symptoms could be a hotter grind. Does the car go like stink in the higher revs?

I was not aware that a local mechanic had rebuilt your cargbs. I have little faith in there ability to do a decent carb rebuild and most lack the ability to balance and flow bench them on completion. I suggest you pull them off and send them to JOE Cutro for a professional overhaul.--Keoke

It's so obvious I can't believe these experts have missed it. It must be the extra weight of all those non-standard parts: GPS, chromed engine parts, cupholder etc.

Roger, Have you driven other Healeys? Is your performance normal at high and low revs?

Hey Tom, nice to hear from you.
Dude, I think you're on to something! You forgot the vanity mirror. Don't think for a minute that dash mirror is used for traffic, lol.

Yes, I've driven other Healeys. Mine seems the same as others.
I'm at Witt's end. I've talked my mechanic into keeping my car and using it as his daily driver till he goes through a full tank of gas. I told him, if he gets 12 mpg...he's now on the hook to find the problem. If he tells me he averaged 16 or above....then I need to go to driving school. He'll get my car in a couple weeks.

A simple point: if you are getting 9 MPG and expecting 13, your fuel consumption is 13/9 what you expect, or almost 50% higher. This is not a small difference, even though 4 MPG may not sound like much.

Big problems are caused by big flaws, not little ones. Spark plug gap is a little one--might affect mileage a few percent, not 50%. And, if the gap were too wide, you'd know because it would miss. Plugs also look OK, maybe a little lean. (You should see mine!) Small errors in mixture also won't cause a 50% increase in fuel use.

So, ignition is probably OK, carbs are probably OK. Are you sure you don't simply have a leak somewhere? Also, (dare I suggest...) have you checked compression?

By the way, I wrote up a section for the Wiki on ignition systems, where I addressed the coil-voltage issue. It's under General Technical Articles|Ignition Systems. About the last three paragraphs under the "Conventional Points-Capacitor Ignition" section.

Hi Steve,
I think you misread my expectations. I'm getting between 9-13 average. I believe BJ8's average between 17-19. If I drive exclusively freeway I may get 21. Just town I get 9-10.

Cheers,
Roger

Anyone besides Keoke, heard of Joe Cutro?
Anyone provide Joe Cutro's contact information?
Cheers,
Roger

Here it is. Joe Curto

Roger,
Joe Curto did a complete rebuild of the HD8s on my Big Healey. They have worked fine since.

Lin

Lin, were you having problems with them?
Did you notice any improvements after?
If so, what?
Did it affect your mpg?
If so, what was the mpg before, then after.

BTW, I think our cup holder article may be in the October Healey Marque.

Cheers,
Roger

You can also check to see if your choke is partially on.This would affect in town driving the most,and not affect hiway driving as much.Are your choke return springs on and working correctly? Choke cables properly adjusted?

Thank you for your input.
That was one of the first things we checked.
I was hoping it was that, for it seemed like a simple fix.
Cheers,
Roger

Haven't weighed in, as I've been pondering.......

But.......

Seems like in my foggy memory banks there was an issue when folks swapped out spring in the slides......

Wrong tension seemed to do that, or the inverse.....

Have you looked at another with same carbs, cleaners off, and lifted the slides, seeing what pressure there was, and checking yours?

Just a random, unconnected thought process......

Although I haven't needed him (yet), he seems to be THE guru.

Ah HA!

The feeble old grey cells actually remembered something!
Found it!

He says that if the spring is too strong, the piston will not rise to its optimum position, thereby causing the engine to run too rich.

http://www.zparts.com/zptech/articles/mal_land/ml_sucarb2/images4/SUcarb_111601d.htm

The condition of two of those plugs shows too rich.
The rest of the engine seems to be compensating, and burning off the fuel.

There may be other issues, but I think I'd check them springs out.

Too thick of dashpot oil will affect operation in the rich sector, by inhibiting the pistion to caome up, effectively keeping the choke on.

Good write-up.

Question:
I re-read all 4 pages (quickly, but not quick enough....my eyes are now crossed), what version AH?

MKI is red spring, MKII is red or green, and a 6-port head is yellow spring.

Paper or oil element on the air filter?

1964 BJ8 phase two. HD8 carbs.

My springs are not colored anymore, maybe because they are old. How do I tell which ones they are?

Also, I noticed that the front dashpot hardly had any oil, but the rear was full. The oil I use is from Moss, SU dashpot oil. My bad for not checking the oil level.

What's your take on the front low and not the back?
What would cause that?

Could I be so lucky to just have the wrong springs? Plus finding out why the front dashpot oil was low?
I'm not out of the woods yet, but I'm hoping for something simple.

Cheers,
Roger

The way these carbs work is on vacuum.
If you read the links, you actually get "pulses" from the intake that can "pulse" the pistons.
One of the reasons the books tell you to have the valves adjusted and ignition right before you start futzing with them.

There was a write-up on using motor oil mixed with machine oil.
Too light an oil will get sucked into the engine and burned.
My presonal feeling is, you don't know where you are with the carbs, as they've been into countless times.
Either send them off and have them "done" right, or get the correct springs and see what happens.

No oil, the piston will "pop" first, leaning the mixture, and the other will try to take over.

I forget...does the HD8 have the button for checking mixture correctness?

The "drop test" is with oil.....should be stiff going up, and a specified time to drop.

But, wrong springs won't be revealed by any of this.
If you take the springs out and wipe them carefully with a rag, no colour is evident at all?

The problem I once had was some yay-who that mixed parts, thinking "all SU's are the same" and one was so different internally, I don't know how the car ran.

The springs are identified by tension, but then you'd have to find some way of testing that.

A) No vacuum leaks? (and see what idle vacuum actually is)
B) Valves adjusted?
C) Compression good and even?
D) Dashpot oil correct and full?
E) Pistons moving freely?
F) Float levels okay?
G) Springs

The springs are cheap and easy to change out. Why not just change them and see what happens. It may be that they are old and weak even if they are the correct ones. One may be weaker than the other do to engine heat. I thought you had your mechanic go over all that. Take charge and learn by doing. Its fun and helps you on the side of the road. Guys like Joe can put it straight and do the testing. Some monkeys polish/sand the piston or inside the housing and that will destroy the suction. Also there is a small hole in the angle tube at the top of the chamber that can get blocked. And do you have open holes in the black caps.

Roger,
My carbs were bought used. My car is a BT7 that would typically use 1 3/4" HD6 carbs. I bought the used 2" HD8s and just sent them to Joe to rebuild before I even tried them. So.... I have no "before" to compare to the "after."

Lin

Hi Richard, yes he has.
I would never re-do what my mechanic has tuned.
Some things I certainly will take charge and learn by doing. I did a nuts and bolts restoration (with a lot of help from the people here on this forum).

My British Mechanic, exclusive of Brit cars for over 40 years, knows more about my Healey then I ever will.

My Mechanic and David Nock have both given my car a full tune up. And that includes checking everything, timeing, drop test, vacuum leak, new spark plugs, wires, etc etc. They both say, the car is running great and the plugs show so.

They can't pin point it and say, just live with the poor mileage, it is what it is.

I just gave my car to my mechanic an hour ago. It will now be his daily driver back and forth to work. He will go through a full tank and tell me what he gets for mpg.

I'm thankful to all the people here who are offering suggestions. I'm relaying them to my mechanic.

Cheers,
Roger

Sticking or slow to rise carb pistons is what I was thinking also.
.. You could have the wrong/stronger springs installed than
standard on top of the carb pistons.
.. Are you using a thick oil such as 30w or 20w-50 motor
oil in your dampers ? If so, try using marvel mystery oil or
some other very low viscosity oil in your dampers.
.. Either your dampers or your pistons could be rubbing/sticking
during normal movement of the carb pistons.

Ed

Somehow I missed seeing the multiple pages of posts when I wrote the above post.
I see that you have moved on to plug gaps and notice that you are now just trying a .035 plug gap.
That is what I have been using with my petronix and matching 40kv coil along with Bosch platinum plugs.
It runs great and I get good mileage 21 MPG average last time I checked.
I use the trip odometer and head to a Shell station after the trip odometer exceeds 200 miles. It seems to take about 10 gallons to fill it back up.

Ed

I didn't notice for quite a while that I had two different dampers installed in my carbs. Who knows where the wrong part was installed ? Maybe the factory ran out of the right dampers one day. Could be the wrong springs in your carbs for the same reason or any previous mechanic may have thought he was helping the way the car ran by installing stronger springs.
Try new springs as others have suggested and change to a low viscosity damper oil to see if it makes a difference. Yes, the lower viscosity oil gets sucked out sooner than the thicker oil but it seems to work better at least in my car. I just check it more often and fill it back up as necessary. I am in there checking the oil and fluid levels anyway.

Ed,

I'm using the recommended SU oil, sold by MOSS.
Why are you using Bosch platinum plugs?
What wires are you using?
You average 21 mpg?
What do you get highway?
What do you get town?

Hi Roger,

Platinum plugs have lasted longer for me than regular plugs in any car that I have used them in. Bosch is a good quality plug but there are other platinum plugs that would probably be just
as good.

I am using Magnecor red wires. I really like them and they keep all of the noise and pops out of my music system. Their design limits current flow because the wire is wrapped like a long stretched spring inside of the insolation. This helps the spark plugs, rotor and cap last a lot longer than if straight metal core wires are used.

I think I am averaging around 20 - 21 MPG. I know it is better than that on trips and less if I drive around town and don't use highways. But I know it is better than 9 MPG around town.
The .035 gap may help your mileage some if you have a 40 KV coil.
As an experiment, take out the SU oil and put in some marvel mystery oil. Also, order a new set of springs for your carbs. Try one thing at a time so you will know if any one thing helps. Do you have matching dampers ?
Good luck in your quest !

Ed

Roger,

FYI I keep a small bottle of 20W-50 oil in the glove box and add a few drops to my HD8s at every fill-up or two. It makes people at the gas station think you know what you are doing.

I'm resurrecting this thread because I have some more info about coil voltage from a new source (ASE master automotive technician, former Sun Electric instructor and 15 years as a technical training instructor for a car company):

"I can tell you for a fact that if you give me 5 minutes with you, a car, and an ignition oscilloscope I could prove their statement 100% false.
Looking at an O-scope trace the only time the voltage will equal the total output of the coil is when the wire is open circuited.
Look at this waveform http://images.picoauto.com/copwaveform.png See the tall vertical line in the middle of the pattern? That is the spark line, in this case it is taking about 18KV to fire this plug. Assuming this is at idle, if we were to snap the throttle wide open the pressure in the cylinder would increase which acts as an insulator, and the spark line needs to rise by maybe 40% or so to let's say 25KV to fire the plug during that period of wide open throttle. So if the spark line is at 100% of coil output at idle, where does that extra 7 KV come from? This right there proves their statement false.
Next look at the almost horizontal line extending to the right of the spark line trending downwards slightly and ends with some oscillations. That is the firing line, and the more powerful the coil, the longer that line is. The less powerful the coil, the shorter that line is. In the illustration, that is a pretty healthy coil, the burn time is about 2 ms. This system can maybe throw 40-50KV if we were to open circuit a plug wire.
But electricity being lazy will only use the voltage needed to overcome the dominant gap in the system, which is usually the gap at the plug.
When I taught scope classes I used to have a plug wire that was cut in half and encased in a clear plastic tube, so I could slide the two ends closer and further apart. Using that it was very easy to see exactly what happened when the gap got bigger or smaller."

-- and --

"The easiest way I can think of to explain it is to think of wattage. 1 volt at 100 amps is 100 watts. 10 Volts at 10 Amps is 100 watts. 100 volts at 1 amp is also 100 watts. Coil output is similar, only instead of amperage think of time. The more voltage required to ionize the gap, the less time the the spark will last. There is a finite amount of power in each discharge of the coil. The more voltage that is used to create the spark, the shorter the time the spark will last (shorter spark line) The extra 10KV never really existed. It is just power that can be used to either ionize the gap, after that any excess power is used to maintain the spark line (keep the fire burning)
some modern ignition systems are capable of 80-90KV outputs, yet their spark lines are between 15-20 KV at idle. where did all the extra voltage go? It is turned into a very long burn time to fully burn the contents of the cylinder.
I agree with you that you can open the gap with a higher performance coil, but as rich as LBCs run, it probably isn't noticeable as it is on a modern car.

yes of course you may quote me and if there are questions, I would be happy to respond."


Not saying I understand this completely--yet--but this seems to confirm my initial belief that the spark voltage is determined by the gap, NOT the theoretical output of the coil.

Hello Roger,

just a thought in an different direction. I understand you have done a tune up , but how did you know your mechanic works well ?
I don´t know how your pertronix realise the centrifugal force controlling. Did you check the centrifugal force controller or vacuum input?

Forget the sparks as reason, they can only be an indicator for bad combustion.



But anyway you live in cheap petrol area... ;-)

Bye Michel-who has an original distributor

Hi Bob,
Just curious which statement he is referring to?

This is the series of posts that prompted this:


Originally Posted By: Bob_Spidell
However, as soon as the secondary voltage has risen sufficiently for a spark to jump the plug gap--or find another path to ground--the coil will discharge its energy and the voltage will rise no higher.

Hi Bob,
That is not how I understand the process. The coil doesn't discharge when it reaches any particular voltage. It discharges when the points open, causing a drop in voltage in the primary wiring of the coil. This change causes the secondary field to collapse-causing the high voltage discharge.


The "new source's" explanation seems to indicate the spark fires when the gap is sufficiently ionized--after the points open--and the voltage across the points varies; i.e. it's not fixed at the coil's theoretical output (which I assumed the reply to my post implied--I may have been mistaken). As I re-read these posts, there may not have that much disagreement. I didn't state it explicitly, but I certainly meant the process happens after the points open. I was actually convinced by the second post that the voltage across the gap would be fixed at the coil's rated output--e.g. 40KV (depending on gap)--but that's apparently not the case.

My main point was that a 'sports' coil won't buy you much in a stock Healey (Austin) engine--unless you're running at high RPM and/or have higher than stock compression--a 'sports' coil will fire at the same voltage as a stock coil all else being equal (the sports coil will support a larger gap, however).

The voltage across the points will always be around 12, give or take a volt or two depending on the charging system . The output of the coil is usually fixed by the ratio of the primary windings to the secondary windings. It is odd that the "new source" interchanges amps with time. I understand what he is saying, but I think it can be misleading and/or confusing. I gotta' get to bed, I have to be up for work in about 5 hours. I'll write more about the time/ amp thing maybe tomorrow.

Cheers

Oops ... meant "voltage across the gaps," not "points." The "source" was trying to explain how the excess power gets dissipated; i.e. with a spark of longer duration.

The scope doesn't lie, but I'm still having a hard time understanding why a coil--a transformer, essentially--that is mathematically able to boost 12V to, say, 40K, will only fire an 18KV spark. Where does the other 28KV "go?"

My 2 cents;

Any coil has a maximum voltage " potential " of x amount of KV.
As Greg has said the ratio between the input side number of turns to the output side number of turns determines the potential maximum voltage that the coil could produce assuming that 12 volts is available as the input voltage.
`
A quick and dirty way to determine the ballpark potential maximum voltage of a coil is to multiply 12 volts time the ratio of the output resistance to the input resistance of the coil. The input resistance is three ohms.
I have not checked my coil but if I did the math right the output side of a 40 kv coil should be in the neighborhood of 1111 ohms. A 20 kv coil 555 ohms. That should be true as long as the coil is not old or damaged.
.
The spark plug gap and the electrical characteristics of the fuel air mixture in the gap ( how easy it can be ionized by the spark ) determine that actual amount of voltage needed to cross the gap. Once that voltage is present at the spark plug gap, the spark happens and the voltage doesn't go up any more.
That high voltage becomes present at the spark plug gap right after the points open or the petronix hall effect transistor stops conducting. That is when the magnetic field of primary side of the coil collapses and that is what induces the voltage on the 2ndary side of the coil.
.
It is good to have as wide of a spark plug gap that can be used by the potential available voltage. The wider the gap, the larger area of hot, ionized material is made to start the ignition of the charge of air/fuel in the cylinder. Thus the wider .035 gap is recommended when a coil with a higher voltage potential or rating is used rather than a standard coil.


Ed

Ed, using points and standard coil, what gap would you suggest? A bit far fetched question, but would the engine then run hotter? And why wouldn't the manufacture (DH) suggest wider gaps?

Hi Bob,
Sorry this took so long, life has been busy for me.
The 28KV still gets used. If you go back to that first section
The energy produced by the secondary windings will remain relatively constant because of the ratio to the primary winding. At the point in time where the dizzy points open, the coil doesn't know how much voltage it will take to bridge the gap at the plug. It is dumb and only wants to bring itself back into equilibrium. As long as the coil's primary windings have enough time to reach saturation, they will produce full output in the secondary when the magnetic field is collapsed. Once the plug gap has been bridged, maintaining the arc takes less voltage so there is an increase in amperage as the voltage drops. So the remainder of the energy is dissipated in this state. You can see where that occurs in the scope graph just to the right of the spike as was pointed out.

Where replacing amps with time is confusing is; all things being equal, adding a higher voltage coil could lengthen the arc time without a change in amperage. So the two variables aren't interchangeable.


I still don't get what he is saying is false? Is it about plug gap? No one in this thread was saying increase the gap for a stock setup. Only that Roger has some higher output parts that would handle the increase without misfiring.

This is a misunderstanding/miscommunication that is entirely my fault. I was convinced the voltage across the gap would be greater with a 'hotter' coil--no one here said that but I took it that way. Anyway, I now have a better understanding; the voltage produced by the coil secondary will be fixed--more for a hotter coil--but won't necessarily be seen across the gap (unless it's required by a larger gap or greater compression, etc.). The extra energy--per the power equation--will be dissipated as amperage across the gaps. IOW, if the coil is capable of producing 40KV per the winding ratio, you won't necessarily see that across the plug gaps; you'll see, say, 18KV at idle and the rest of the energy will be current.

Right?

Yes, that is my understanding of how it works. There is a book you may be interested in reading called "Performance Ignition Systems". Here at Amazon. The author holds several patents and has his own line of systems. I'm actually using one of them in my Healey.

Hi Tahoe,

A standard coil will work best with the standard recommended spark plug gap.
...
D.H. made his recommendation based on his available coil at the time. He didn't have a 40 kv coil to play with or if he did, he knew the factory wouldn't agree to the increase in cost per car.
That would be my guess.

Ed

Bob,

What you have stated is right...
Now comes the advanced part of the situation.
How much current flow do we want to allow after the spark happens ?
Once all of the fuel/air is ionized in the spark plug gap,
how much more current is really needed or desired ?
We have plain wire spark plug wires with little resistance to current flow .
Then we have wires that are designed to limit current flow Immediately AFTER the spark happens such as carbon fiber stranded conductor wire and wound conductor wires like Magnacor wires.
Limiting the unnecessary extra current flow is desirable for
prolonging the life of the spark plugs, wires, rotor, points or electronic trigger, cap, and coil plus there is less of a drain on the electrical system of the car. It also prevents the car's ignition system from acting like a radio station and transmitting signals ( pops and whining noise ) to your car's music system or the computer system controls in a modern car.

Ed

Hey guys,

Being my springs are old and don't have any color on them to tell me if they are the correct ones, I've ordered a set (green on one end, red on the other end of the spring) from Moss. That should eliminate the spring question.

The next question would be if I have a vacuum leak. I've tested the vacuum unit and it's fine. No leak in the copper tube to the carburetor either.

How do I test for this:
The SU carburetor is highly vacuum dependent for its operation. Vacuum leaks at the throttle shafts are a common problem on these carburetors, these leaks allow unmetered air into the mixture and prevent the piston from raising properly due to the lack of vacuum in the system.

Something about spraying carb cleaner there?

It is a rough test but yes if you spray carb cleaner or even WD 40 around the shafts, etc, with the engine running and the rpm's increase or smooth out it is an indication you may have some air leaking around them which can be fixed with a rebush.

Also try timing the drop of the two pistons from all the way up to when they land on the floor of the carb--the time should be about the same and differences can indicate wear on carb bore or piston or both.

Yeah, you just need to make sure how you spray doesn't allow the mist to go in through the air filters giving you a false reading. Were your carbs re-bushed when they were rebuilt? Be careful with high flash-point cleaners around the exhaust. Non-flammables can show a leak by lowering the engine speed. You might want to hit the carb-to-manifold stack also.

Did you check the vacuum line to the brake booster?

Greg,
First time hearing about that.
Would you explain what I check for and how that affects things.
Thanks a lot,
Roger

Check for crack along the hose, maybe a loose connection at either end. If it's old, might as well replace it for cheap insurance. The hose taps into the manifold vacuum so it would have a similar effect as leaky gaskets on the carb spacers.

Hi Roger,

I am getting 11 mpg in moderately spirited urban driving. FYI.

Thanks Tom for putting that out there.
I don't jack rabbit start and I'm an easy driver. I get between 9-12 on fill ups.

Are Tom and I the only guys that get 9-12mpg urban driving in a BJ8?

Others say they average 15-19 ???
Anyone else want to post their average mpg?

Cheers,
Roger

"Anyone else want to post their average mpg?"
------------------------------------
My average mpg is 22-24, perhaps 1-2 more for sustained two-lane highway travel at around 65-70 mph average. This is with a five-speed Smitty box and a 3.55 diff.

Going for bragging rights Michael?
I was hoping for an apples to apples (BJ8) comparison.
Thanks anyway Mr Healeyota.....Healey/Toyota.

Cheers!

I get 15-16mph around-town driving, 18-19 hard driving (mountain roads, freeway @ 75+, etc.) and 23-24 on the highway @ 55-60.

18 to 22 mpg. Are you running standard size tires?

Me? 185/70 Vredesteins.

No, Roger's BJ8, but its good to know.

I have a BN7 and get 15 mpg around town. It is running a little rich (black carbon on the bumper above the exhaust.

Rich,
You may have solved the case!
I have Michelin ZX 175R 15

Here's a photo!

You didn't photo shop the colors and smile. I'm disappointed. I have that tee shirt.
See you this weekend? You are probably in the winner's circle.
Rich

I haven't checked my "town" mileage in forever, but I could easily get 9 MPG here in the traffic I suffer through in San Antonio. High temperatures and several long stoplights that take three cycles to get through - and then creeping along at 10-25 mph equals poor mileage. Quite a change from when I lived in a small town in Oklahoma where it was really unusual to have to sit through more than one light sequence. Just a thought: Do you spend a lot of time idling when in town? If so, it would greatly reduce the mileage you get in town.

Hi Stever,

Yes, I do... all of the above. Idle at stop lights, creep in traffic 10-25, get on the freeway, but not for long etc.

Todays post is to let anyone who has been following this post and to all those who offered their input, I go my carbs back the other day. I sent them to Joe Curto Inc in NY about 3 weeks ago. One week each way with UPS.

Here's what he wrote on the invoice:
Replaced throttle shafts/worn
replace main jets (blue ones oversize hole)
repin choke arms
auc 8156 main jets
drop test OK

I'm hopeful that these changes will help improve the in town driving mpg.
Before putting them back in the car, I spent a little time with the polishing wheel. Those who know me, would expect nothing less. The carbs may not give me great milage after all this, but they sure will look nice in the engine bay. (Nothing chromed here boys. Just a lot of polishing time spent wet sanding then polishing all the aluminum and metal parts.)

I'll post later down the road and let you know if my average mpg increased or not.

Cheers,
Roger