Hunt for a vacuum leak

[handala]

Hi Folks....

I'm hoping someone can shed some light on my vacuum problem.

stock 1F engine on 1974 FJ40. Rebuilt the carb a few months ago. I have had problems with the engine running rich. I've done several things including replacing the manifold gasket which helped with the vacuum leak. at this point, it pulls 15 mm Hg on idle when warm, but this is not very consistent. I did a vacuum check with a gauge (covered the carb airhorn), and the vacuum still spikes before the engine stalls, suggesting I still have a leak.

I did a smoke test, and identified smoke coming out of two spots. one is the idle mixture screw, and the other is from a ? hinge at the base of the carb. just above the spacer, facing forward (see pictures).

Is this normal? if not, I'm going to replace the idle mixture screw with the original one that was on the carb before i rebuilt it. but what about the leak at the base of the carb through the hinge?

thanks in advance!

Sani

 

[1969FJ]

Well, no vacuum leak is normal. You figured out the problems.

 

[thebigredrocker]

Fuel weeping off the end of the throttle shaft is normal. There is no seal on the shaft. When the engine is running, fuel is sprayed at the shaft, but manifold vacuum prevents the fuel from wicking out to the end of the shaft. After shutdown, the residual fuel is drawn out by capillary action, possibly getting a drop on the end of the shaft.

That is your secondary throttle shaft that leaked smoke. My guess is throttle shaft and your mix screw aren't the main cause of your problems.

Did you sand the intake flat before the new gasket went on? Have you adjusted the valves?

Low vacuum could also be a poor performing distributor. What dissy setup do you have?

 

[Pighead]

Try advancing your timing a bit and see if your vacuum improves as you do...

 

[katwalk]

Following. I have been fighting a high idle issue the last few days and found/fixed a couple vacuum leaks between the intake and the head. When I spray a little carb cleaner where the butterfly shaft comes through the front of the carb, I get the slightest increase in RPMs. Other than that I can not find any more vacuum leaks but cant get the idle below 950-1000.

 

[handala]

Thank you for the input

@thebigredrocker...I did not sand the intake flat, but I did run a flat ruler agains the edge of the intake and header, and did not notice any substantial warping etc... also I spent a lot of time spraying carb cleaner around the intake/header with no change in RPM. may not completely rule that out as the problem, but for now does not seem to be the source. if all else fails, i may need to take it apart and have it machined.

also, recently adjusted the valves and I don't see the fluctuation with vacuum that suggests a valve problem as the source of the leak.

I have a non-USA distributer that is 15 years old and recently changed points and adjusted gap.

@Pighead .... i'll try advancing the timing and see what happens.

thanks again

 

[77mustard40]

I found my leak by spraying carb cleaner around the base of the carb and along the top and bottom surface of the intake manifold where it mounts to the head. Did so with the engine running work one small area at a time, if your idle increases you found a leak.