backfiring through carb
 

im sure this has popped up multiple times, but here it goes again. i have a 72 c20, i replaced the valve covers/gaskets, spark plugs/wires (spark plugs were gaped before installed to .035) after all of this was replaced it started backfiring from the carb, the motor is a 327 off a 67 camaro, my brother and i adjusted the timing and made sure the wires were put on correctly, it idles fine but as soon as i give it a little gas it starts popping from the carb, i sprayed a little carb cleaner in there but im still getting the backfire, i replaced the old vacuum lines, and plugs, my brother said that it might be a loose or messed up valve, im pretty lost now id appreciate any advice or possible solutions

thanks in advance

Re: backfiring through carb
 

Could have a bent exh pushrod so the fuel comes in the intake and can't excape out the exhaust valve so fires from compression and exits back out the intake vave which is the carb. Remove covers and run at idle or even unhook coil wire and ground and turn over engine and watch each rocker arm to see if it moves up and down the same as the others, could even be bad cam lobe but prob a pushrod or even broken rocker arm.

Re: backfiring through carb
 

Just double check the wires firing order first.. 18436572. Have even seen a rocker stud partily pull out of the head so look at their length also.

Re: backfiring through carb
 

thank you for the help, im definitely going to try that tomorrow, i have the truck idling right now, i am hearing a tick from the passenger side valve cover

Re: backfiring through carb
 

we redid the wires when we replaced them, the previous owner was careless with the truck

Re: backfiring through carb
 

A tick is usually a loose rocker arm, which could just be not adjusted enough or the rocker stud pulled up a bit so would act as loose. The rocker stud isn't a very common problem, only usually happens when an engine is over reved. But they are only pressed in not screwed so ya just back to pulling covers and having a really good look at each rocker arm and it's lift. The running it part when idling makes it really easy to see quick but can be a bit messy, that is why most would just turn it over and watch. good luck, you will get it. I went back to the double checking plug wires because I have done it myself and would have bet I got them all right, but didn't.:lol:

Re: backfiring through carb
 

Just remembered something else, you said it is a 67 engine with plug gap set at .035 so that means you have points, right so could be the condensor, it will make it backfire also. old school stuff. If you do switch up to HEI distrib you can open the plug gaps to .045 and get a bit more performance out of it and also a few more mpg, just a thought on the condensor.

Re: backfiring through carb
 

im going to check the valves tomorrow, there might be a loose one, i heard its really messy and tons of fun haha, but first thing ill do is double check the wires, the distributor is pretty big, i know its not stock, ill check what its called

Re: backfiring through carb
 

its a delco remy

Re: backfiring through carb
 

X2 on the Condensor.
If its points type

Re: backfiring through carb
 

If you are not sure which distrib you have just check to see if it has a separate coil then it has points and plug gap is .035 if it has a coil in the top of the cap then it is electronic and a HEI type so plug gap is .045

Re: backfiring through carb
 

http://www.delcoremyhistory.com/imag...ght-810w-1.jpg

it looks like this one

Re: backfiring through carb
 

http://www.delcoremyhistory.com/imag...ght-810w-1.jpg

it looks like this one

Re: backfiring through carb
 

That is an HEI
Check the plug gap, confirm proper plugs and firing order check timing ( base timing and total advance) if all checks oit---> check valve adjustment.
Don't use champion plugs in an HEI

Re: backfiring through carb
 

huh...... do you think its the spark plugs? i was on an embarrassing budget and bought the crappy autolite plugs....

Re: backfiring through carb
 

Hpoefully the plug wires are better, I just changed my full set, were Taylor 8.8 wires only 1 year old with about 1,000 miles on them and 3 were dead lately and had a small backfire at idle or downshift with a manual trans, so if they are new that is good but hopefully a good name brand set. can do an ohm meter check on each wire also if that is a concern. I agree on the Champion, never use them except in a Ford.

Re: backfiring through carb
 

Just out of curiosity, how did the engine run before you changed the wires?
Did you drive it? Was it unresponsive or running with a miss?

Re: backfiring through carb
 

Was sitting here wondering when setting the timing, what is your base timing with vacumn advance hose disconnected, the normal around 12degrees and when you reconnect the vacumn line at idle does it stay the same or go up. Reason asking is that is the vacumn line should have no vacumn or very very little at idle as to not increase the base timing setting until the engine Rpm is raised then the vac canister should start to work and increase timing, so just making sure it is connected to ported vacumn no manifold (full vacumn) at idle. Just thinking of all avenue's. Like the question before mine though of how as it running before you changed the wires and plugs. Also won't make it run worse but pull the plugs and open up the gaps to .o45 for future running of engine so that is correct for HEI distrib.

Re: backfiring through carb
 

I would check timing.

Re: backfiring through carb
 

What kind of carb is it? Is it a Holley?