73-87chevytrucks.com

73-87 Chevy _ GMC Trucks => 73-87 Chevy & GMC Trucks => Topic started by: gold84gmc on August 30, 2007, 03:24:28 pm

Title: backfiring
Post by: gold84gmc on August 30, 2007, 03:24:28 pm
ok, so i ran the truck today and let it get to operating temp. and a couple of times when i gave it a quick rev it backfired out of the carb...and a couple of times outa the exhaust.....does this sound like the timing is off to you?
Title: Re: backfiring
Post by: VileZambonie on August 30, 2007, 03:33:45 pm
either that or your firing order is incorrect. Make sure no vacuum leaks and the choke is adjusted properly
Title: Re: backfiring
Post by: gold84gmc on August 30, 2007, 06:23:34 pm
alright, i checked the plug wires, and they are in the correct order.
Title: Re: backfiring
Post by: stefjeano on August 31, 2007, 07:58:15 am
Your cam might be going bad!
I will get worst!
Title: Re: backfiring
Post by: VileZambonie on August 31, 2007, 02:09:30 pm
What about the choke and vacuum leaks? Did you check? Is it only if you snap the throttle?
Title: Re: backfiring
Post by: gold84gmc on August 31, 2007, 03:01:22 pm
yea its only when i snap the throttle. i kno there is a few vacum lines that seem loose.
Title: Re: backfiring
Post by: j-dub-u on September 01, 2007, 08:25:52 am
Sounds lean to me.....and since it only happens when you snap the throttle, could be a busted diaphram on the acc. pump.  ???
Title: Re: backfiring
Post by: gold84gmc on September 01, 2007, 11:22:58 am
any way i would be able to figure out if its the acc pump without tearing the carb apart?....what is it anyways, a q-jet? (its the factory 4 bbl)
Title: Re: backfiring
Post by: VileZambonie on September 01, 2007, 02:07:22 pm
The factory 4 barrel was a Rochester Quadrajet. If you depress the accelerator pump plunger all the way down with the engine idling it should stall the engine if it's working correctly. That's a quick ez check. Check around for vacuum leaks
Title: Re: backfiring
Post by: gold84gmc on September 01, 2007, 03:33:39 pm
http://dyeager535.topcities.com/CCCqjetdiagram.html   ...anyone know what part in the diagram is the acc pump?
Title: Re: backfiring
Post by: gold84gmc on September 01, 2007, 03:36:21 pm
http://img214.imageshack.us/img214/8404/quadrajetjpg6zj.jpg    oh wait, is that it?
Title: Re: backfiring
Post by: DnStClr on September 01, 2007, 05:58:09 pm
yes. That's the plunger.
Title: Re: backfiring
Post by: gold84gmc on September 02, 2007, 11:26:39 am
ok so i pushed down on the plunger and the engine revved up as if i had pushed on the gas pedal.
Title: Re: backfiring
Post by: VileZambonie on September 02, 2007, 03:04:31 pm
You only depressed the plunger right? You must have some serious vacuum leaks.
Title: Re: backfiring
Post by: gold84gmc on September 02, 2007, 03:46:25 pm
oh, am i supposed to push down only on the pin thing, not on the "rocker" thing?
Title: Re: backfiring
Post by: VileZambonie on September 02, 2007, 06:53:53 pm
uh huh
Title: Re: backfiring
Post by: gold84gmc on September 03, 2007, 11:49:17 am
ok, so i pushed down on just the plunger piece not the rocker arm thing, and the engine did not stall. the rpms went down but that was it.....so does that mean the carb needs to be rebuilt?
Title: Re: backfiring
Post by: VileZambonie on September 03, 2007, 07:13:27 pm
If your RPMs went up I'd be looking for a serious vacuum leak.
Title: Re: backfiring
Post by: gold84gmc on September 03, 2007, 07:38:27 pm
no they went down
Title: Re: backfiring
Post by: VileZambonie on September 03, 2007, 07:56:22 pm
I would say that your accelerator pump is probbaly no good. Rebuild the carb
Title: Re: backfiring
Post by: gold84gmc on September 03, 2007, 08:16:28 pm
http://www.4wheelnoffroad.com/qjet.html  ....so does that website seem thorough enough to follow for the rebuild?
Title: Re: backfiring
Post by: VileZambonie on September 03, 2007, 08:40:29 pm
Sure just get some epxoy and seal up the fuel wells underneath as the factory plugs tend to leak and drain the fuel bowl into the intake manifold reulting in hard start - long cranking