Novice question about vacuum advance line.

[1michael]

Hello all, I am in the process of putting back together a 61 BT7 that has been apart for 25 years or so. The question I have is in regard to the vacuum advance line. Common sence tells me it should be plumbed to the inlet on the top of the rear carb body. However, I have found another vacuum inlet on the bottom of the intake manifold toward the front. Should it go there? If not, what is the second inlet for?

Any advice would be helpfull.

Thanks

Michael

 

[Keoke]

Hello all, I am in the process of putting back together a 61 BT7 that has been apart for 25 years or so. The question I have is in regard to the vacuum advance line. Common sence tells me it should be plumbed to the inlet on the top of the rear carb body.
However, I have found another vacuum inlet on the bottom of the intake manifold toward the front. Should it go there?------No.
If not, what is the second inlet for?--- They are Fuel Drains which should be fitted with a pipe similar to the Vac line formed into a lazy Z and exit the bottom of the car via a guide bolted to the pan.--Fwiw--Keoke

Any advice would be helpfull.

Thanks

Michael

 

[healeynut]

Michael -

The two little ports you see on the far ends of the intake manifold are not vacuum ports. They are drain ports for excess fuel for when you are using the choke. Excess fuel in the intake manifold can lead to premature upper cylinder wear.

You have to get the little copper tubing and fittings so that the fuel drains are properly configured. You can get this from the usual suspects.

 

[GregW]

Hi Michael,
I have a BJ8, so the vacuum line may be different. As far as I can tell, mine hooked up here (on rear carb). I don’t use a vacuum advance and I have Mikuni carbs now.

 

[GregW]

And the pattern starts all over again.

 

[MarkA]

How do these manifold fuel drain ports work? Do they ever fail? I have been trying to track down a vacuum leak for a while now. My idle speed slows way down when the engine is hot. I am thinking that I have a vacuum leak when cold and then it goes away when hot.

What do you all think?

Mark

 

[Keoke]

How do these drains work?--- Gravity; They simply provide an exit for excess fuel in the inlet manifold
Do they ever fail?----Yes it is very common for the steel pipes to fracture at the fitting. Might produce a vac leak but it is doubtful. However, that's one of the reasons the pipes exist is to prevent potential vac leaks. I have been trying to track down a vacuum leak for a while now.

My idle speed slows way down when the engine is hot.---That is a bit unusual the idle usually increases when hot.

I am thinking that I have a vacuum leak when hot and then it goes away when hot.---Could be, but it should be the other way around I would think, but it is not uncommon for the main vac pipe from the manifold to the dizzy to fracture/rust out behind the rear of the engine block.

What do you all think?

Mark

Testng using a flexible vac line from the manifold to the dizzy and blocking the drainports should allow to access if these sources are the problem.--Fwiw-Keoke

 

[MarkA]

Do the drain ports stay closed under vacuum, but then open with the engine off to allow the draining?

I have blocked off the dizzy vacuum port when the engine was warm with no change in idle speed. Did the same for the brake booster port still with no change. I sprayed carb cleaner around anything vacuum related, both with the engine hot and cold, with no idle change. I will try blocking the drain ports.

Unless it is not a vacuum leak which is causing my problem....??? Hmmmmmm........

Thanks!

 

[Keoke]

Do the drain ports stay closed under vacuum, but then open with the engine off to allow the draining?-----
No as I indicated earlier reducing the potential for a vac leak at the drain ports is accomplished by using the long drain tubes formed into a lazy "Z" shape.

I have blocked off the dizzy vacuum port when the engine was warm with no change in idle speed. Did the same for the brake booster port still with no change. I sprayed carb cleaner around anything vacuum related, both with the engine hot and cold, with no idle change. I will try blocking the drain ports.

Unless it is not a vacuum leak which is causing my problem....??? Hmmmmmm........May not be. Dizzy Vac port at the carb may be blocked with carbon build up ?--Keoke

Thanks!

 

[glemon]

Mark, it is not uncommon for these cars to idle slower when hot, the idle speed will pick up initially as engine WARMS and the oil temp rises (and viscosity thins) but it is not unusual for the idle to fall way down when the motor gets HOT (as in idling in traffic on a hot summer day hot) because of higher intake air temp, fuel vaporization in the system, or both.

Band-aid cheap approach turn up your idle speed in the summer.

More expensive approaches cooling system upgrades such as electric fans or re-cored radiators.

For reasons unknown the hot slow down phenomenon seems to be worse in old tired engines than in fresh ones, at least in my experience.

I do not suspect a vacuum leak at least in what you have described so far.

The drain ports serve a purpose which is to prevent or at least diminish raw fuel going into the cylinders, gas is nowhere near as good a lubricant as oil, the drains do their job with the motor on as fuel should not be pumping with the motor off (or at least with the ignition off). I would not block them for long term operation of the car.

Good Luck, Greg

 

[MarkA]

Hi Greg,

It seems to richen up when the engine gets hot. With (California) cool air temps, I can do a 30 minute freeway drive and not have a problem. But, do the same with 85/90 degree temps and the problem starts. I would think that the hot engine/air temps would cause things to lean instead of richen. The coolant temps stay down below 170 deg with hot air temps. The problem is worst in stop and go traffic on hot days when the coolant temps do rise up to 180-190. Then, press the clutch pedal and the engine will stall (my throw-out bearing is dragging a little too much!).

The side of my right shoe is starting to wear out... When the clutch goes in on hot days, I need to keep a little extra speed on the engine. One of these days, I would like to get this resolved.

Mark

 

[Keoke]

Hi Greg,

It seems to richen up when the engine gets hot. With (California) cool air temps, I can do a 30 minute freeway drive and not have a problem. But, do the same with 85/90 degree temps and the problem starts.
I would think that the hot engine/air temps would cause things to lean instead of richen.---------

---No it is possible that increasing the inlet air temp also decreases its density which would result in richening of the mixture.

The coolant temps stay down below 170 deg with hot air temps. The problem is worst in stop and go traffic on hot days when the coolant temps do rise up to 180-190. Then, press the clutch pedal and the engine will stall (my throw-out bearing is dragging a little too much!).

The side of my right shoe is starting to wear out... When the clutch goes in on hot days, I need to keep a little extra speed on the engine. One of these days, I would like to get this resolved.

Mark

I have only experienced this problem when tuning the carbs. If you depress the clutch and the engine slows down you are on the wrong side of the curve, usually this takes only a small adjustment to correct. Otherwise neither of my cars exhibit this problem. I set the idle just a bit below the hot running point when tuning and it settles at about 800 RPM when hot.---Fwiw--Keoke

 

[MarkA]

Keoke,

Which side is the wrong side of the curve, lean or rich? What are good idle speeds? I have always tried to go with the book value of 600 RPM, which always seemed slow to me. How do you set the idle?

Thanks,
Mark

 

[Keoke]

Keoke,

Which side is the wrong side of the curve, lean or rich?
--It can be either way but in my case I am usually too lean.

What are good idle speeds?
I usualy set it at 1000 RPM on the car Tach which is ~ 800 RPM om my penskie analyser.

I have always tried to go with the book value of 600 RPM, which always seemed slow to me.---Me Too!

How do you set the idle?
I use the mixture screws and the tickover screws to smooth it out. In other words I fiddle with it.--Keoke- /bcforum/images/%%GRAEMLIN_URL%%/laugh.gif


Thanks,
Mark

 

[healeynut]

Do the drain ports stay closed under vacuum, but then open with the engine off to allow the draining?

I have blocked off the dizzy vacuum port when the engine was warm with no change in idle speed. Did the same for the brake booster port still with no change. I sprayed carb cleaner around anything vacuum related, both with the engine hot and cold, with no idle change. I will try blocking the drain ports.

Unless it is not a vacuum leak which is causing my problem....??? Hmmmmmm........

Thanks!

Mark -

This is very common with most british cars. As the engines get hot, dissimilar metals cause different rates of expansion, opening up some leaks in the system if you haven't replaced gaskets & rebuilt carbs. So first thing you need to do is make sure all of your manifold gaskets are in good shape.

The fuel overflow drain pipes aren't your problem - you will draw the same amount of vacuum through these holes hot or cold.

The most common cause of this symptom, I have found, has been typically when throttle rod bushings are worn in the SU carb throttle bodies. The throttle rod is brass and the carb body is aluminum alloy - when it gets hot, leaks can form around the throttle shaft where it goes through the throttle body, esp. if the bushings are worn out (very common).

On HD8 carbs the fix is easy - just get new teflon bushings from British Car Specialists and follow the instructions for installation. For other SU's they should be sent to a specialist like Joe Curto for proper brass re-bushing and bench testing.

 

[MarkA]

I appreciate all of the help on this…

I have rebuilt the carbs. The throttle shafts are in good shape with new Teflon strip bushings. I didn't change the shafts since they were not worn.

Earlier, I said that it leans out when hot. I mean't that it richens up as the engine compartment heats up. When driving around on cooler days, I don't have this problem. With the engine hot, I have sprayed carb cleaner all around the intake system with no engine speed change. I even tried it with ether (quite scary!) and still no change.

I have leaned the mixtures out to the point that it starts "rumbling" on deceleration. It definitely seems to be loading up when idling and hot. I do not want to lean it out any more since it will start popping. I get 20-22 MPG, so I don't think that the mid and high ranges are too rich. Tail pipe is a little on the dark side and sooty, but I attribute some of that to oil burn. I think the rich problem is only in the idle range.

What else??? I will turn up the idle speed. It seemed a lot happier with a higher idle speed. I guess it time to start fiddling and play around more with the mixtures.

Mark

 

[healeynut]

Mark -

When you rebuilt the carbs, did you replace the needles? If the needles are worn or incorrect, they can really mess up how your car runs.

I would check your needles.

 

[MarkA]

Alan,

I used master rebuild kits. I did replace the needles with the original sizes.

Mark

 

[Johnny]

Just my 2 cents here, but you said you rebuilt the carbs. Did you replace the needle's as well? They do wear and need replacing. Go through the assembly procedure again and make sure you don't have any gasket failures, even new one's can fail.

The intake manifuld also has a vacumn hole on the top rear section that should be plugged. The fuel drain lines should be kept open, not plugged. Replace them if they're clogged, same with the vacumn line. BCS will sell you enough of the 1/8" copper tubing you need to do all.

 

[tahoe healey]

Just a thought or two but are the needles setted properly and exactly the same at the shoulders? Did the markings on the needles match the old ones? Did you use new damper springs of the proper color for your carbs? Lastly, are the butterflys closing with out binding and are they opening equally when the linkage is moved?