hello all, its been awhile, but i have a problem. i have a 4barrel quad on a 1980 305 v8, and the idle is perfect and if i slowly rise the rpm its fine as well, but if i floor the gas i get some backfire out of the carb. my shop teacher cant seem to find the problem out "grade 12 auto", but hes pretty new so it may be something obvious. our timing is set at 4 degrees. and that seems to be what its supposed to be for the model of the engine, so i dont think its timing.

 

recheck your firing order. switching nos. 5 & 7 can cause that

 

Is the firing order the only reason a car would backfire or is that just one of the many possible reasons? Of is that just unique to our fox body camaros?

 

there are many reasons for a backfire to occur. The one that I was referring to is, on a sbc, cylinders 5 & 7 are right next to each other(both physically and in the firing order). When swapped, the engine will appear to idle normally but, when accellerated it will pop and spit like its the end of the world, only to go back to normal at idle once again. Most other reasons for backfiring are related to valve and spark timing.

 

Or a lean condition.

 

try to cover the carb inlet with your hands to see if it idles up, then bring the rpms up and the same with one hand, if the rpms come up then you have a lean condition

 

wtf?

 

The accellerator pump is worn out in the carb. If you look at the lever on the carb and operate the throttle you will see that the lever pushes down a rod that goes into the top of the carb. This provides a squirt of fuel so the engine does not do what yours is doing. You will need to lift off the top of the carb to swap out the part. Look down the carb bore and open the throttle quickly and see if there is a good firm squirt of fuel on both sides.

 

Sounds like a lean condition to me. I would guess it either needs a bigger shot from the accel pump or a different size power valve.

 

If he has a Q-jet,it does not have a power valve or different sizes for the accellerator pump.

 

Being a 1980 model, I would assume it does not have computer controls. If that is the case, 4 degrees initial timing is not enough. 8-12 would be more like it.

 

Oops missed the part that he had a q-jet

 

Anyone ever consider the possibility of a vaccum leak? I had one once and it was doing about the same problems, it would idle pretty normal and i could accelerate at a slow slow pace and no backfire, but when given more gas it would backfire and stall, let off the gas and it'd be fine. At idle i could hear a really mild pop though, you had to really listen.

Idk though, the vaccum leak would have more extreme symptoms i would think, i guess if you felt up to it you could take carb cleaner and spray it around the base of the carb and then the base of the intake manifold to the heads and see if you hear a idle change. depends, i'm just throwing things out there...

 

Yes, I had the same problem. The cause was the gapping of the spark plugs. The previous owner had them gapped from .30 to .50. I gapped them all to .45 and haven't had a problem since. Also, do check for if it's too lean. Check out plugs on that matter. If they're white and dry, then it's too lean, if they're dark and dirty then it's too rich.

 

Fox body camaro? Is that what u get when u mix a mustang and a maro?

 

what does the f mean in f-bodies?

 

I means it isn't an A-platform, or a B-platform, or a C-platform, or a D-platform, or an E-platform or a G-platform, or an H-platform, or an X-plateform. . .

http://en.wikipedia.org/wiki/Category:GM_platforms

 

Hello everyone I just bought a 92 Camaro RS 25th ann. V6 3.1l , I have a backfiring issue, I have replaced cap and rotor plugs and wires as well as the ignition coil it idles fine and this back fire is small (not a big bang). where else should I look I need advise from outside the box.??? THANKS

 

Talk about bring a thread back from the dead. Seeing as you have MFI, you obviously aren't having the same issue as the OP was. So is the back fire coming from out your exhaust, or through the throttle body?
C.

 

Wow he totally hijacked this thread and brought it back from the dead!lol