Intake Manifold Leak

[mike zahorik]

I've been helping a friend revive a 1913 roadster, which he had just inherited from his grandfather. After a couple weekends we successfully got the car started and safe to drive. BUT..... we have been having some trouble with hot starting. I installed a battery for starting and that has helped with both cold and hot starts, but after the engine has come up to operating temperature, shut off and let stand for 10 minutes, the engine will not start. I suspect an intake manifold leak. I did check out the carburetor, it's a Holley NH, not correct, but we are looking for a functional car right now. It is clean and the float level is correct. The fuel tank and sediment bulb were replaced a few years ago and is very clean. The fact that the car starts rather well cold tells me that the carburetor is probably ok.

I have seen plenty of intake manifold leaks on Model T's and generally new rings and glands along with plenty of RTV will fix this problem. Is there a way of actually detecting or testing for a manifold leak? I have tried pouring oil over the port. They say the exhaust will turn blue, well with a seasoned engine, the exhaust is already kinda blue. I've seen guys use unlit propane torches. They say the engine RPM will go up, but this seems a little daring being so close to the hot exhaust manifold. I've even made a small aluminum plate that mounts between the carburetor and the manifold which has a small tube to sample engine vacuum, but that is also suspect. I don't see much difference to point to a leak.

Anyone have any other method. I'm sure that after the intake is removed and properly installed the leak(?) will be gone. Maybe that is the best way anyhow. Thanks Mike.

[RGould1910]

I was advised to use carb cleaner and it worked. Ran the engine at high idle and sprayed where the manifold contacts the block. If there's a leak, you'll hear an obvious stumbling. Worked very well for me thanks to a suggestion from a forum member.

[Bruce Compton]

If it "starts well cold" then it's probably not a manifold leak (which would give a lean mix). I suspect that the needle valve in the carb is leaking a little or the float is set too high causing a rich mixture, or the mixture adjustment is too far open.