Thread: Exhaust backfire, carb related?

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I have a chain auto supply reman carb (q-jet) that has been plauged with problems. From previous posts, it was suggested that I had float problems. The idle circuit is impossible to adjust, it runs pretty good at about 1200 RPM and over, it smokes black, if I stab the throttle, it will idle (a little high) for a few seconds and then die, and last but not least, it pops/backfires through the exhaust. The last part is what is bothering me. Will an over rich condition cause modest backfiring? The other symtoms say float level/needle & seat problems. (thanks by the way to everyone that has pointed me in this direction in the past) I can take the carb back where I got it and get a warranty exchange, but I don't want to return it if there could be another issue causing this. I have reservations about taking it apart and by default voiding my warranty. The timing is set, the points and dwell are adjusted, good plugs, etc...
Has anyone had problems with reman carbs from one of these chain stores, or am I just lucky like that?

Originally Posted by 65ny

The timing is set, the points and dwell are adjusted, good plugs, etc...
Has anyone had problems with reman carbs from one of these chain stores, or am I just lucky like that?

I ran into a guy with a 350 in a boat a year ago and it was backfiring and ran rich etc. I could have sworn the timing chain skipped a tooth. He had a new carb in it. (Quadrajet) We played with it for hours adjusting the timing etc. I even threw in my distributor from my boat. We changed the plugs, coil etc, and his friend a mechanic, said it was the carb. I figured no way. They bought another carb, and it ran like a charm. He wasted an enitre week of fishing.

So maybe you are just lucky like that. Do you ever go fishing? Do you catch any? This guy couldn't catch a fish either.

I must be lucky,.......I exchanged the carb for a new (reman/old) one. This one didn't load up though. Good! It would also idle, a little rough, but better than before. I started adjusting the idle mixture and I soon found out that I could turn both screws all the way in (idling at around 600) and the engine didn't even stumble.....................What the h***????? Metering rods incorrect? probably. I have sworn off cheapo depot parts. I can envision some carb rebuilder picking mismatched parts out of several bins and churning out carbs assembly line style. Every time I have tried to save a few bucks and get the cheapie stuff, I regret it in one way or the other. You would think I would learn. I think it is time to buck up and buy a new one. Or maybe I will try to rebuild one of these old cores I have sitting around, I could do that for peanuts.....................................

Yep, and I am going to give them another opportunity to toss this one around again.

[QUOTE=65ny]I must be lucky,.......I exchanged the carb for a new (reman/old) one. This one didn't load up though. Good! It would also idle, a little rough, but better than before. I started adjusting the idle mixture and I soon found out that I could turn both screws all the way in (idling at around 600) and the engine didn't even stumble.....................What the h***????? Metering rods incorrect? probably. I have sworn off cheapo depot parts. I can envision some carb rebuilder picking mismatched parts out of several bins and churning out carbs assembly line style. Every time I have tried to save a few bucks and get the cheapie stuff, I regret it in one way or the other. You would think I would learn. I think it is time to buck up and buy a new one. Or maybe I will try to rebuild one of these old cores I have sitting around, I could do that for peanuts.....................................[/QUOTE

Sounds like you have a vacume leak somewhere..... Also do you definirely know your distributor is good ??? When did you last check it ? What Imean by check is pull the cap of look at the general condition... Reach down and grap the rotor, give it a twist against the advance spings, does it snap back cleanly ?

You know the end for the old saying... "I can do it for peanuts.............and end up with monkeys". Better to do it right, do it once.

i've never had any luck with reman carbs from parts stores.... i've pulled them apart and found that the jets are different sizes, parts are missing, parts are installed wrong, and my favorite, they're missing a screw so they just JB weld it together.... in the shop its gotten to a point that i just make customers buy brand new carbs or get the one they have rebuilt... which i send it out to FSP they swap out a rebuild of the exact same carb or updated model of the carb.... and i've never had one come back with problems

Southerner--

I thought of the vacuum leak too. Didn't find any. Where are you going with the distributer thing? I was just in it yesterday checking things out, and making sure everything is as it should be. Are you saying I should be looking for something else???
I agree with you on doing things right the first time, I was just jabbing at myself a little with the comment about doing something for peanuts.

Originally Posted by 65ny

Southerner--

I thought of the vacuum leak too. Didn't find any. Where are you going with the distributer thing? I was just in it yesterday checking things out, and making sure everything is as it should be. Are you saying I should be looking for something else???
I agree with you on doing things right the first time, I was just jabbing at myself a little with the comment about doing something for peanuts.

Yup, sometimes the distributor advance mechanism sticks due to old sticky grease and oil or grit, rust or a spring has become worn or is broken, missing.
What happens is that the advance can stick at differnet degrees of advance, this changes the engines habits at idle or in the higher revs. You adjust for one lot, go for a drive come back and it's "off" again. Does have the potential to drive people bannanas because of the constantly changing circumstances. So check your advance manually as described. Then if you have a timing light, hook it up disconnect the vacume advance and plug it, point the light at the timing mark on the balancer and bring the revs up on the motor say to 1800 rpm The timing mark on the damper should advance (walk up ) smoothly, if it doen't and/or jumps around you know you have a problem with the distributor. Oh and when you take the revs back to idle the timing mark should be back down to where you set it.
Good luck with it. MIke

I'm going to point this out again. If you can turn the idle adjustment screws in and it doesn't make any difference, your throttle plate is open to much.

like mike said, sounds like a vac. leak, or what Mikej said, if it is you can put all the carb. on you want to and still have the problem, unless the leak is the carb. the mikes has the last say on this one. three mikes cant be wrong.