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Back firing !

New User
Posts: 8
Joined: 08/13
Posted: 08/30/13 10:36 AM

I just put a 1996 302 truck motor in my 1987 LX Mustang. Every time I let off the gas it back fires very loud. I put a holley 600cmf carb. on it and a new distriber on changed to exturnal fuel pump. Does anybody know whats wrong ? Confused  

Post Reply
Posts: 124
Joined: 03/13
Posted: 08/31/13 07:49 AM

i am taking that the backfire is in the exhaust....

not out the carb...

look for exhaust leaks...  what type of exhaust did you install...

what did you do with the original thermactor air injection system..

87 mustangs probably have a pipe that bolts to the back of the cylinder heads.. or across the back of the exhaust manifolds..  if that is leaking air... the small tear drop shaped gaskets got left off..  it can leak enough air that causes the exhaust to pull air into the exhaust system and when you close the throttle.. the rich air fuel mixture now has enough air to explode in the exhaust system..

if you have a shop vacuum.. or a leaf blower... you might be able to .. with a COLD exhaust system..  duct tape the nozzle to your muffler outlet and turn the blower on.. then move your hand around the exhaust system on the engine to see if you can feel any air leaks...  

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