TR4/4A TR4A mixture problem - need advice please

[Adrio]

I have been struggling with the mixture on my TR4A for some time now and I am throwing in the towel. As such I ask,no I beg, your collective advice as I am at the end of my rope.

My TR4A was a frame off restoration 2000 miles ago and it has the HS6 SU carbs. Both carbs have new:
the 0.100 jets
the standard (TW) needle
needle and seats

The engine was rebuilt with new rings, bearings, honed liners and a rebuilt head with new valves and hardened seats. I checked the compression today and it was 130 on all four.

The symptoms are: it is running rich, both at idle and on acceleration (and I suspect at speed). The fuel consumption is high. The jets are all the way up (full lean, I can't make it any leaner and all the physical things are correct the jets are just above the bridge) and the needles are installed in the right place (at the shoulder etc.). The float levels are correct (I checked them several times today). When the car is cold I need choke in order to accelerate or else I backfire but that goes away as soon as it get up to operating speed and it seems to run ok other then the black smoke. The plugs are sooty and the colortune shows a rich mixture at idle and when I open the throttle.

What do you all think is the solution to this problem.

 

[NutmegCT]

Just plunging in after solving a similar problem on my TR3A with H6 carbs -

Is the timing set correctly?

Tom

 

[MDCanaday]

You need to drop your needles down in 50 thou increments untill you can get the mixture in the range of adjustment by the jet nuts. Also make very sure you dont have excessive fuel pressure or bad float valves. Fuel pressure should be no more than 2.5 lbs.
Good luck!
MD(mad dog)

 

[KVH]

First, at least for me, I always look for something simple.

So, like Nutmeg says, check the timing to make sure you're not experiencing something dramatic due to materially incorrect timing. You should static time the car with a bulb off the coil, 4 degrees BTDC. Correct point gap and good condenser assumed.

Next, assuming your floats really are correct, make absolutely certain that you are using a fuel filter and that your float needles aren't sticking due to "crud" from the tank. There should be no debris where the needle hits the seat. My needles gave me fits until I replaced them, and one brand was defective.

Now on to your carbs. There are various needles for the TR2, 3, 4 and 4A, so with a gauge be sure you've got the right ones. If you do, I'd next check that your jet assembly moves freely up and down at the instance of the spring on the pivot bar. It should slide up and down, and when up it should be near perfectly flat with the interior base of the bridge in the carb housing. Your needles must be centralized, of course, meaning that when the jet is pushed up in its highest position, flat against the interior bridge, as each piston is lifted it falls naturally with a ping--in other words there is no binding from the needle when lifted and dropped.

Then, at least for me, I open the nuts 12 flats, a bit rich. But my experience is that the number of flats won't materially impact performance if you're off by just 2 or 3 flats--that's what makes your condition suspicious. The textbook instructions never applied to my TRs.

Finally, be sure your linkages are proper, with both operating at the same time, with no binding, and with both balanced with equal air flow.

Good luck. I'm no expert, but I hope it doesn't show.

 

[TR3driver]

You didn't happen to install Grose Jets, did you ? If so, my first step would be to pitch them and go back to standard float valves.

Then check fuel pressure, right at the carbs, when the problem is happening. (Tee a pressure gauge into the line with a long hose, so you can bring it out from under and prop it temporarily under a wiper blade.)

Then I would double-check that the float valves close securely and don't leak. (With the lid off the bowl, lightly hold the float up while you blow into the fuel inlet. Should take no pressure whatsoever to completely shut off the flow of air.)

If still no joy, I'd change the floats. I've spent way too many hours fighting with plastic floats that only float when they are cold; which sounds a lot like your problem.

One more thought, has the weather been unseasonably warm for where you live ? Might be that you've got "winter fuel" and it's boiling in the heat.

PPS, other things to check : Exhaust not plugged up (like a collapsed tube in the muffler), and valve clearances correct.

 

[Adrio]

Updated information for you folks. Firs, thanks for the help so far.

My float valves are the standard type. And I did set the timing correctly using the static method. I checked the valve clearance at 500 miles after the rebuild (that is 1500 miles ago). The petrol is new as of yesterday.

I never had this problem with my TR3A but then again the carbs are a bit different.

I am curious about the plastic flats that don't flat when they are warm. Tell me more. Though my problem seems to be there all the time.

Whould I have these 130 pound readings if I had assembled the engine with the timing chain off by one tooth? I am grasping at straws here but I think that is all I have to grasp at. Also is the lowering of the needle by .050" a standard proceedure? I was thinking of ordering the lean needle but would this lowering do the same thing?

One other thing I did not say is that when the head was rebuilt is was ported, does that make a difference to this issue?

 

[Don Elliott]

Adrio - I'd put the old needles back in. When I have a problem, I ask myself, "What have I changed ?" Then I go back step by step.

 

[Adrio]

I would have tried the onld needles but there were none. This car was a frame off restoration that I aquired in boxes. The old carbs I got were both front carbs and on had no needle and the other was bent. I got the rear carb from a friend who happened to have a spare and it too had no needle.

In short there was nothing I had changed, the car has been like this since I got it together.

 

[KVH]

Are you sure your point gap is correct?

Is the engine "otherwise" running smooth?

Are you sure 130 isn't low for compression? I'm almost certain mine was 170 in all four cylinders after a valve job last year.

The jet needles are a pain. So, despite all you've done and said, make sure they match and that you've got the original equipment, standard needles.

About the timing chain, I'm sure that would be a problem, but I don't know if it would cause your symptoms.

 

[Adrio]

I was wondering about the 130 myself, that is why I mentioned it. And that is what lead me to the timing chain question.

Otherwise the engine seems to be running fine, but the idle is a bit "lumpy" (sort of sounds like a harley). At times it does not idle and I have to turn the idle screw a bit.

As to the points and gap. I replaced the entire ignition system 2 gas tanks ago (points, plugs, cap, coil, wires, condensor and rotor).

This one has me baffled. My TR3A has the same engine (slightly different carbs) and I have always been able to get it running like a top over the past 25 years.

 

[NutmegCT]

My 1959 1991cc engine has 170 compression in all four cylinders. Never rebuilt as far as I know.

Adrio - what rpm does your engine idle? Does it hold that idle? One of the continuing mysteries on the forum is TR3/4 engines which won't idle below 1500 or so. I found I had a binding accelerator linkage. Plus, a bent jet (!), mis-matched incorrect (?) needles, frozen and incorrectly set choke, and a few other goodies.

Also, are you using the "spec" needles (SW=rich, TW=standard, C1W=lean) and .100" jets?

And of course, the eternal "enough oil in the dashpots"?

Tom

 

[Don Elliott]

Did you fill up with Sunoco or PetroCan ? Both have ethanol added. I had trouble with the one time I used Sunoco a few weeks ago. I also had trouble in USA where all gas has at least 10% ethanol. I switched back to Shell and Esso here in Canada. The problem has gone.

 

[Adrio]

To answer the question:

Yes I am using the Standard TW needle and .100" jets.
I did make sure the dashpots have enough oil

I did fill up at PetroCanada, that is an interesting point about the ethanol.

The others having 170 pounds compression has me wondering. what sort of numbers do the resto of you folks get for compression on these engines. I figured since all four were exactly the same the rings and valves were OK. Is there a way to check if I have the timing chain on correctly without taking the chain cover off? Again I think this is grasping at straws but I have to hold on to something or I will fall /bcforum/images/%%GRAEMLIN_URL%%/smile.gif

I spend a good part of yesterday trying to work out this issue and I am getting upset with it. I am having thoughts of selling the car and buying a sailboat that has no engine to wrestle with. /bcforum/images/%%GRAEMLIN_URL%%/frown.gif

 

[piman]

Hello Adrio,

you seem to have checked just about everything on the carburettors. Dropping the needles in the pistons is not an answer as it doesn't address the real problem. (incidentally neither does the needle you have fitted matter at idle, as just about every needle has the same idle dimension, any variance is no more than 1 thou in diameter)
I certainly would do a valve timing check, and the easiest check is to remove the rocker cover, get the engine to TDC number one firing and see what number four cylinder valve positions are; they should have as near as you can tell equal lift. To help with this, rotate the engine until one valve just closes (number four cylinder) mark the crank damper then reverse the engine until the other number four valve just closes and mark the damper. The marks should be equal distance either side of the damper TDC mark.


Alec

 

[Adrio]

Thanks Alec,

there is one more observation of my carbs that I made. If I lift the dashpots by hand (engine off) I do not feel resistance for the first little bit then I feel the damping kick in. Again, the oil in the dashpots is at the correct level. Is this normal? And could it be a hint as to my problem.

 

[TR3driver]

Hmmm, lumpy idle, low compression readings ... are you sure that's a stock camshaft in there ?

There is a small amount of play in the dashpot dampers, but not much. If you can move them more than 1/8" with no resistance, then there is probably something wrong with the damper. However, that wouldn't cause the idle mixture to be wrong, the dampers only come into play when you open the throttle (and even then the effect is temporary). It should idle fine even with the dampers completely removed.

If you lift the dashpot pistons to the top and let them fall, do they land with a distinct click ? Any binding or rubbing can upset the mixture.

I'd check the cam first; but then I'd be wondering if someone grabbed the wrong needles or metering jet. You might try measuring them; the bore in the jet should be exactly 0.100", while the part of the needle just below the shoulder should be 0.099".

What springs are in the dashpots ?

 

[AltaKnight]

Hi Adrio....
My experience is with my TR6 and twin ZS carbs different from your HS6's but I think your problem is with the float level.
I had a tough time with mine setting the float height correctly since using the routine and dimensions in the manual gave a very rich mixture that I couldn't adjust out lean enough.
I resorted to removing the float bowls in-situ, tricky to do (not sure if that's possible on a HS6), and looking at the gas level in the bowls dirrectly, then it was obvious.
I just tweaked the float tabs until i got it right by trial and error then set about adjusting the mixture properly, after about 6 months I finally got it where the plugs are a perfect tan colour.

 

[Adrio]

I can't be sure about the camshaft originality. I know the history of this engine only back to 1970 when the son of a friend bought the TR3 it was in. Fron that point to now the camshaft as not been changed. But the engine ran fine in the TR3 (with the TR3 SU carbs) up until 1974. So there is no way for me to be sure it is a stock camshaft. It is a Stebro exhaust so it does sound a lot louder then my TR3 stock exhaust and that may be tricking me a bit. but the engine vibrates side to side more at idle then my TR3 but not a lot.

As to the springs in the dashpots, I can't tell which ones they are as any hint of colour is long gone. They are the same as each other. And I have swapped the oned from my TR3 into the TR4 and the same problem occurs.

I am pretty sure I can lift the dashpots more then 1/8" before I feel resistance. I will check it when I get back home from work and post the exact amount. I do get the distink click when I drip the dashpots. The needles have the TW stamped right on them. I don't have a way to measure the size of the hole in the jet and there is no other marking on the jet I can find to confirm they are the right ones.

 

[Adrio]

Thanks Graham,
speaking of float level, I can see the float level if I remove the dash pots and look down the jet hole. What is the corect level for the fuel to be? Just at the top of the jet or some distance down? If the later what distance down.

I can see an issue here in the the front carb has the bowl infront and the rear carb the bowl is in back. With the engine in a nose high attitude the front carb would have the fuel level higher in the jet then the rear carb (for the same float level in the bowl.

 

[AltaKnight]

The fuel level should be below the top of the jet by about 1/4inch would be my guess (perhaps others know exactly), the venturi effect of the air intake through the carb passing over the top of the jet sucks up the fuel and atomizes it; I don't think the level is real critical since the carb has to operate going up and down hills but I know for sure from personal experience if it's too high you will never get it leaned out properly. I'm not real familiar with your carb but if the area around the top of the jet is wet with fuel that would be a good indication it's too high. The mixture adjustment usually adjusts either the needle or the jet (that the needle goes into) up and down but this can't overcome a fuel level that is too high in the bowl and will always result in running rich.