The Stovebolt Site Forums The Shop Area Engine Shop Engine burps

I have recently finished timing my 235, as well as putting in new points, condensor, and rotor. The engine runs fine and smooth at idle. If you gradually increase the RPM the engine continues to run smoothly. However, if you "blip" the gas pedal the engine "burps"--not really a backfire type noise, more like a burp from the engine bay. When it burps the engine hesitates and almost quits. Could this be a carburator problem? What do you think? Thanks.

It sounds like a carb. problem. With the engine off look down the throat of the carb & move the accelerator. You should see a squirt of gas going in the throat. If not the accel pump may be bad. The float level might be low. Try advancing the spark a few degrees & see if it improves.

Greg,

Good advice from Lenexa...I would ask, is the engine warm when you try this? Even the best tuned rig can burp when cold. While poking around in there, make sure the vacuum advance 'flips' when you 'blip'. It should move as the carburetor is worked.

Stuart

Yeah, the engine was cold--I tried blipping the gas right after I started it up. The good thing is that it seemed ok later in the day after we started it up again and let it warm up (it is fairly cold here now).

I don't understand why the engine temperature would make a difference in this case. The spark/timing is mechanically linked, as is the fuel pump. Why would it make a differnce if the engine was cold?

I probably jumped the gun with my original post, but I feel the need to understand why things happen the way they do. This is my first time working on an engine like this, and I don't have the luxury of experience to tell me what I should accept, and what is abnormal. Thanks guys!

Greg,

Since I am now on the plus side of sixty, I can appreciate being warmed up before being 'blipped'.

My guess is that the fuel doesn't vaporize as well at the lower temperatures and won't mix as well with the air. The cold intake runners and associated engine parts tend to pull and sling the fuel out of the mix and things just don't work as efficiently until the rig is up to operating temperature.

Stuart

Not to mention the thicker oil and resulting tighter clearances in the engine are giving resistance,trying to keep the engine from picking up revs until it's warmed up.
Speed

Stuart and speed, your comments make a lot of sense. As I said in a previous post, it is sometimes hard for me to determine if something is wrong, or if it is just part of normal "old chevy character". In this case, I think I'm going to consider it part of normal "old chevy character", although I am now more motivated to purchase the manifold heat valve spring that I noticed was missing. Thanks for your thoughts!

A cold engine needs a richer fuel mixture. If your accelerator pump isn't up to snuff the stumbling (burp) will be worse with a cold engine. The vast majority of cases of this type of problem I've experienced have been the result of a faulty accelerator pump.

If your engine hesitates & bogs when cold & runs fine when warm you have the ideal condition. That is the poor mans tuneup machine. That,s why they put chokes on them.