Inliners International Forums General Discussion Engines Back firing on a 250

Can someone tell me what causes back firing? I just put a new carb on it and changed my cap, rotor, condenser, and points and it's still running really bad. Someone told me to check my timing but I've been playing with that and it's still ain't doing it.

Back firing through the carb?

='s lean condition,vacuum leak?

Spark plug wires incorrectly installed,firing order off?


MBHD

It's back firing from the exhaust pipes.

Do you have access to a timing light? Also... if the points are not set right it can cause that. Sometimes they wiggle loose after you have set them.

a friend of mine came to look at it today and told me that my carb is getting too much fuel. After he almost closed the mixture screw it was still getting too much fuel.
Any thoughts?

Exchange the carb,seems like it was not rebuilt correctly.

MBHD

If you look around on the "Old Car Manual Project" there may be some rebuild manuals for your carb. I found one for mine on there. They are not all PDF some are just JPEG pictures of a manual so it takes a while to download after you find what you need.

If you have any questions post your year model vehicle and whatever you know about the carb and I might could find it for you. I think its tocmp dot org ... or just type in Old Car Manual Project.

The year of the car is a 1970 with a 1bbl. carb. I believe they told me at the part's store that the carb calls for a 1972.
It's a mono jet Roschester.

Generally speaking,back firing from the exhaust can be an iginition problem or leaky exhaust valve.

I remember years ago working on VWs and when we put headers on them they would backfire constantly. WhAt fixed it then was changing the main jets on the carburetor, and everything would be fine again. I suspect that is your problem, improper fuel mixture on the main jet. you can get different sized jets at the auto parts store. I Don't know which ones to get though bigger or smaller. I don't remember.

Carb Manuals - I gave the wrong address for carb manuals. They did not have one listed for the monojet but here is other info on Rochesters.
http://www.newagemetal.com/pages/Chevrolet/index.html
http://www.newagemetal.com/pages/Chevrolet/71/index.htm
http://www.oldcarmanualproject.com/manuals/Carbs/index.html
The files are just JPEG scans of tech manuals and are slow to load on dial up. Sometimes you have to look around on that site because they have several URLs but they have lots of good info.

Thank you. I found out that it was the carb that was rebuild wrong. It's horrible, it took 4 carbs rebuild by Holley.
They were missing parts or rebuild wrong. I should of got my money back from the parts store but I was being the nice guy.
Today I was working on my last one which runs good except there's a small hole with an adjustment screw below the float that suppossed to be capped with lead or something and it isn't. Now is leaking fuel out of there. I guess I can cap it with something after I adjust that screw.

If you look around on that site it links to another site... Old Carburator Guy or something like that.
He has information on Brazing the floats and there may be some answer to your situation.
There is an article in there how people put the wrong braze on the floats and then they dont weigh the same.
Look around on there and if I find the article I will post a link.

Thanks