Backfire in intake manifold.

[General]

My engine is running great now. (Thanks to everyone who gave me advise to get it there!) The only problem I have is that occasionaly I get a small backfire back up through the intake manifold. This usually happens when I push down quickly on the gas. As you all may remember, the engine is the original 250 straight 6. Single cylinder Rochester Carb. I figured it was the timing but after a new chain and adjusting the timing to perfection, still poof! about one in five times. Is it my carb or could I still have timing problems. I could live with it but I'm afraid that eventually this will cause damage to my carb...

Here's a picture of the engine, maybe looking at it will help.
http://home.earthlink.net/~choirteach/photogallery/66engine.jpg

 

[Glen]

Have you put a timing light on it? Still could be firing a little off. Do you possibly have a valve sticking? If an intake valve is sticking open, you can some backfire through the carb. Some people swear by Marvel Mystery Oil. A little in the crankcase is suppossed to cure sticking valves. It either has to be timing or valves. Good luck.

 

[bk65]

Make sure your timing advance is working properly as well. I had a similar problem where I'd time it right to specs at idle, but it would still not run like it should. Turned out the mechanical advance was stuck. Had another car that had the vacuum advance canister on the distributor had been changed to make it advance about twice as much as it should.(They can be swapped out to advance it more or less.) If you've got vacuum advance, check that it's working and has the correct canister. Good luck.