need help asap

[UP GRADE]

hi, everyone this is the problem i am having. the last few week my truck has a loud backfire. sound like a 12 gague shot gun. what is going on. the carb has been rebuilt and it's still doing it, new plus and wires and timing set dead center. the motor has about 7 or 8 thousand miles has something went wrong inside the engine. i need help bad. thanks UP GRADE

[sleric77]

I was having the same problem and a mechanic told me that I had too much carb , but I didn't believe him. So about two months later that engine slung a rod . I don't know if that was the cause but I should've checked into it. My .02 .

[Myself]

What do you mean timing set dead center? Did you change anything before the backfiring started? Maybe your coil is going bad.

[LockDoc]

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I'm not sure what you mean by 'the timing is set dead center'. To me "dead center" would be "0". If it is set at "0" that would be incorrect. Is it backfiring through the carb or out the exhaust? There are a few different things that could cause either one. There is a good chance that either one or more valves are open when they shouldn't be or you are getting gasoline buildup in the exhaust system. Other things that might cause this are jumped timing chain, cracked distributor cap, burned valves, bent valves, and a multitude of other things. More info would be great. i.e.: How long ago was the carb rebuilt? What is the timing set at exactly (degrees advance)? Any other problems that might be associated (high temps, noises, loss of coolant, rough idle, etc). The more information the better...

LockDoc

[UP GRADE]

loc doc it's backfiring from both. the carb was rebuilt about two weeks ago. when the engine had ran for about 30 min. there is no more backfring forgot to mention that in the first post

[68gmsee]

If it's backfiring out the muffler, it's usually unburned fuel escaping through the exhaust valves. Bad valves can cause it as well as any part of the ignition system like bad spark plug, plug wires or distributor.

I blew my muffler out once because I had a badly fouled defective spark plug. It was letting unburned fuel escape and as I was reving the engine up it blew...

[joe231]

you have a points distributor?
had the same problem on the '66
new points adjusted correctly fixed the problem

[70GMCer]

Maybe he means dead center as far as the cam & crank gear go.

[ChevLoRay]

Originally Posted by UP GRADE

...sound like a 12 gague shot gun...

I guess you need to be mindful of where you drive in Memphis if your truck is backfiring, huh? I'm gonna bet that you can have a lot of folks ducking for cover....

If you have a Q-Jet carb, they have an inherent problem with fuel leaking into the back (secondary) of the carb from leaking plugs in the bottom of the bowl (part of the air body).

Timing is also an issue.

Are you running an HEI or points-type distributor?

[UP GRADE]

i'm running HEI and EDELBROCK 650 CARB.

[ChevLoRay]

Don't know about your carb, but the 1405 I had (manual choke) ran rich. It would gas-foul the plugs around town and just before the plug (#2) bit the dust, there would be quite a loud backfire.

HEI shouldn't be an issue.

[piecesparts]

Let's clear this up!!! What do YOU mean by the timing is set on "Dead Center"? It should be set at about 8 degrees BTDC minimum setting and possibly set further to get more performance. Are you checking it with the vacuum line disconnected from the dizzy?

I have run a few of the Edelbrock 1406 carbs and a couple Carter carbs of the very same design (yes, they are exactly the same carbs) and have never had an overcarb issue with a small CFM rating of 625 CFM on a standard chevy V-8. If you actually have an Edelbrock carb, is it the AFB design carb or a replacement carb for the stock trim? If it is backfiring, due to overgassing, then the carb has a flooding issue. Just out of curiosity, what are the idle mixture screws set at on your carb.

[Big Block]

I didn't have a ground clip on my coil inside HEI cap and it backfired through the exhaust and blew out one of my mufflers. It would sound like a shot gun going off. Burned up two coils and pick up module before I found out what was causing it. Good luck finding your problem.