The Stovebolt Site Forums The Shop Area Engine Shop Vacuum Leak Somewhere

I recently experienced an abrupt lean condition on the road with my Carter YF 2100S. It kept stalling out and needed the choke at operating temperature. It was running great for about 200 miles after having a bushing put in the throttle body. When I pulled the carb off, I discovered that the guy that put it in only put one on the pump lifter side of the carb. Is that OK or should both sides of the throttle body be bushed?

Also, is it a "best practice" method to use two gaskets, one under the carb insulator with another on top of the insulator when mounting the carb on the intake? I have one under the insulator and another on top of the insulator and I can't tell if the leak is coming from under the insulator or from the throttle body shaft itself or from somewhere else in the intake. All hoses and connections check out fine.

Is it possible to get a fairly good vacuum reading when tuning a carburetor but still have a leak somewhere else that hits all of a sudden and stalls out the engine? Any input you guys would have is greatly appreciated.
Thanks,
Mark

A vacuum leak can often be detected with an unlit propane torch. When fuel is being sucked in rather than raw air you will know it and will have found the source of the leak.

A normal vacuum leaks causes high idle speeds, very seldom do they stall out. Are you sure it's getting the proper amount of fuel?
A vacuum gauge will read low if you have a leak. Try the unlit propane torch around the base of the carb, speed will increase with the added fuel if it finds it way in.

The one bushing may be all the carb needed if it was on the linkage side where all the pulling force is.

Thanks. What's puzzling to me is that I set the carb with a vacuum gauge and got a good reading at least 17" - 18" with a smooth idle. Than maybe 50 miles later it wouldn't run without the choke pulled halfway out. So it's sucking in air somewhere.

So I'm not sure if putting a gasket under the insulator may have caused a small leak or it's somewhere else. Finding vacuum leaks are sometimes a puzzle wrapped in an enigma.

If it runs only with the choke out, it may also mean you have a jet or passage partially plugged in the carb. As directed above, try the propane trick to see if you can find a vacuum leak. I would also suspect a piece of something in the carb if you just had it all apart.

a gasket above and below the insulator should be ok. Remember, a gasket is supposed to be softer than what it is placed against and help to seal minor surface imperfections.

I run gaskets on both sides of the insulator on my 216 with no leaks or problems.
You can use an unlit propane source or carb cleaner to spray around gasket sealing surfaces and the carb itself to see if the idle picks up. You can test for how much it will pick up by spraying alittle around the top of the carb when it's running.

I swag the float is either getting hung up or stopped up or you're not getting enough fuel to the carb.

Good luck

If an unlit propane torch shows no vacuum leaks, check the linkage at the rear of the carb for the accelerator pump. Sometimes they don't get assembled properly.
I had a similar problem as you once, and I opened up the carb and found a check ball sitting in the bottom of the float bowl.
I don't know how that happened, but I put it back where it belonged and everything worked after that.
Carl

I plan on looking for the vacuum leak first thing on Saturday. If no leaks are found I'll open the carb up. You mentioned the check ball. A lot of times that gets overlooked and falls out. Thanks.