Car Backfires when Started/Just replaced exhaust and rebuilt carb

[longdillon1]

Hello. I just replaced the stock exhaust and took out all of the smog stuff from my 75 vette. The car runs but after a few minutes the carb seems to load up and it backfires alot. What would cause that?
Thanks

 

[Rodney Gold]

Backfires are almost 100% due to a lean condition or a vacuum leak when it comes to carbs. I woud look for vaccum leaks first as you took off all the EGR stuff - check the intake manifold for any open tubes. Best is to buy a cheap vacuum gauge to see what manifold vac you are pulling , its a great diagnostic and tuning tool as well. The new manifolds might also be the source of your problems as they might be more efficient and now you are running lean - also check that the manifold gaskets arent leaking and that the exhaust isnt either. When does it backfire - on acceleration or at steady state?

 

[JohnZ]

And does it backfire through the carb, or through the exhaust ("afterfire"). ?

 

[longdillon1]

I guess it was after firing then because it was coming through the mufflers. It did it about 25 times. what causes that?
Thanks
Dillon

 

[Vettehead Mikey]

Looking at all your similar threads, it sounds like something went wrong with either your carb rebuild and/or removal of the smog equipment.

 

[73shark]

After you get done checking for vacuum leaks, check your timing.

 

[6880 Mike]

...check your timing....

I agree.

 

[2VettesMike]

One other thought depending on the carb/filter setup is to check the fuel filter and inlet, could have debris restricting fuel flow.

Thanks

Mike

 

[longdillon1]

well one of the needles in the carb was slightly cracked. When I took the top of the carb off it broke off. I am replacing the fuel filter and want to time it. what is the best timing degree? My car originally had smog equipment since it was a 75 but I tool it all off when I converted it to true dual exhaust. Thanks For all of the suggestions and hope to hear more.\
Thanks

 

[Vettehead Mikey]

If you've got a stcok distributor, use the stock timing. It should be written on the emission sticker on the firewall or in your shop manual.