Engine backfires

[Anonymous]

hi, thats my problem, the engine backfires ONLY when i let off the gas pedal at 2000 rpm or more, sounds like BANG!! PAPRAPRAPRAPRA!! the engine was recently rebuilt is a 170, i have a holley 1bbl carb (new), and a distributor with vacuum advance only, new sparks and wires, the engine only has 6-2-1 headers, the rest is stock.

what´s happening??

i hope someone can help me

bye!

 

[Anonymous]

It could be many things, I can't think of them all right now but a leak in the exhaust thats letting fresh air in is one.

 

[gtm1086]

Try bumping up the timining and richening up the fuel mixture

 

[CobraSix]

Sounds like the timing is really retarded. Start there, then check your spark plugs to see if its running rich/lean.

Slade

 

[Anonymous]

Is it backfiring or after-firing. Backfiring is spitting back up and out the carb. Typically lean conditions, vacuum leaks and retarded timing cause back firing. After-firing is the result of extra fuel being dumped into the exhaust and igniting there. It sounds like you have after-firing. Too much fuel is dumping into the exhaust when the throttle plates are closed and create a high manifold vacuum pressure. Float setting could be high or the idle jets a bit big. You will see after firing on road racers as they spit fire out of the exhaust when engine braking. I think some afterfire is normal with a manual tranmission.

I don't have any Holley carbs, but maybe a Holley expert will chime in and tell you if it could be power valve related.
Doug

 

[Anonymous]

thanks for the answers, yes is after-firing, i have free exhaust and manual transmission but i have friends with the same "configuration" and runs normal, my problem is basically in the carb?? i have to adjust the timing? i dont have the lamp.

BUT I DONT remember if the problem was after i put the headers

maybe i can try to insert a exhaust cone like a supertrapp to see if the problem is there....

 

[addo]

Is it the correct carb for your distributor? It really does sound like delayed timing and that could result from use of another carby that's not compatible.

 

[Anonymous]

When You say "free exhaust" what do you mean? Do you not have mufflers on after your headers? With no mufflers or louder mufflers, the after-fire will be more pronounced than a stock set up.
Doug

 

[Anonymous]

mine did that once....but not that bad. it was just one pop and once i put on my petronix wires and flamethrower 2 coil it stopped. now all my car does is roast the damn aircleaners. hopefully my new carb will fix this problem.

 

[addo]

Remember that the carbing specs/types might have been different in Argentina, too. That's why I suspected incompatibility. The new carb may be pulling too much vacuum at all times; and thus retarding the vacuum-only distributor too much. Result: backfire.

 

[Anonymous]

Are you running a Pertronix?

 

[Anonymous]

Remember that the carbing specs/types might have been different in Argentina, too. That's why I suspected incompatibility. The new carb may be pulling too much vacuum at all times; and thus retarding the vacuum-only distributor too much. Result: backfire.

i have a holley 1908 carb, the original one but new, but the distributor could be the problem because every falcon produced in argentina came with centrifugal and vacuum advance, i dont know which argie car my fomoco distributor came with.

yes, i have no mufflers but i have a lot of friends with the same free exhaust configuration and no one has my problem, BUT no one has my old vacuum advance distributor.

 

[Lazy JW]

You need a new distributor.
Joe

 

[Anonymous]

yes, i am going to buy a new distributor

thanks