The 1947 - Present Chevrolet & GMC Truck Message Board Network







Register or Log In To remove these advertisements.

Go Back   The 1947 - Present Chevrolet & GMC Truck Message Board Network > 47 - Current classic GM Trucks > The 1973 - 1987 Chevrolet & GMC Squarebody Pickups Message Board

Web 67-72chevytrucks.com


Reply
 
Thread Tools Display Modes
Old 03-04-2005, 01:54 PM   #1
bbchevy
87 Wanna Be K30
 
bbchevy's Avatar
 
Join Date: May 2003
Location: long island, new york
Posts: 218
backfire... KA-POW!!!

what causes backfire on a carburated motor. the choke is unhooked and when the motor warms up it will backfire and lack just about all its power going down the road. mixture too lean? too rich? i cant even pull the truck out of the driveway. maybe the plugs arent fireing? double checked all the wires and they are all going to the correct cylinders.wires and plugs are all new. so is the cap and rotor. yea i think im lost
bbchevy is offline   Reply With Quote
Old 03-04-2005, 02:00 PM   #2
Prerunner1982
Registered User
 
Prerunner1982's Avatar
 
Join Date: Oct 2002
Location: Edmond, OK
Posts: 5,904
sounds like your timing maybe off...
Prerunner1982 is offline   Reply With Quote
Old 03-04-2005, 02:21 PM   #3
1974gmc
In Progress
 
1974gmc's Avatar
 
Join Date: Feb 2005
Location: Kamloops, BC, Canada
Posts: 312
i had the same sorta thing, when it got up to a certain rpm it would backfire and gutless as hell. but it ended up being the collector gasket blew out
__________________
1993 Chevrolet K2500 454 4L80E
1974 GMC 1/2t 2wd Stepside 305 auto *sold*
1985 Ford Mustang GT 5.0 5spd
1974gmc is offline   Reply With Quote
Old 03-04-2005, 04:46 PM   #4
RockHQ
ROCKET POWER!
 
RockHQ's Avatar
 
Join Date: Feb 2003
Location: Finland, Europe
Posts: 509
It's running lean. You have a vac. leak somewhere, or the carb is not functioning properly.
__________________
What did i do last nite?
I had a wonderful time,
That's what they tell me
What did i do last nite?

1979 C-10 shortfleet: Olds 350, Th400, 12 bolt
Current project: 1969 Olds 455 W-30, needing a rebuild
RockHQ is offline   Reply With Quote
Old 03-04-2005, 05:47 PM   #5
NeCrOmAnCeR
Registered User
 
NeCrOmAnCeR's Avatar
 
Join Date: Feb 2004
Location: Hodgenville, Ky
Posts: 735
Backfire out of the carb is to lean
Out of the tail-pipe is to rich.

But be sure your timing is correct too.
NeCrOmAnCeR is offline   Reply With Quote
Old 03-04-2005, 06:01 PM   #6
JonnyTechMech
STOP! Hamma time!!!
 
JonnyTechMech's Avatar
 
Join Date: Feb 2005
Location: Dallas TX.
Posts: 145
Sounds like the timing to me. Did you put a Timing Gun on it yet?
__________________
Plan your work and work your plan!!!, or pitty da fool!!
87 GMC BaseTrim, 305 under the wrench/TH400/
92 Chevy 1500, 350,TH700R4 sittin on dubs
JonnyTechMech is offline   Reply With Quote
Old 03-04-2005, 06:09 PM   #7
Hoods69BadBowTie
Chevys Kick A$$
 
Hoods69BadBowTie's Avatar
 
Join Date: Jan 2005
Location: Zootown, MT
Posts: 12,699
Yeah, I was having the same problem and it was my timing. Either that or a vacuam leak.
-Later
__________________
*HOODS is what I answer too*
-'79, '77, '88 Pickup Sold, '85 Camaro, '83 T/A, '81,'83,'90 K5 Blazer All Sold
-'79 3/4 ton "Big Yellow Bananna" Lifted 4spd. 39.5 TSL Swampers, The money Pit
-'86 K5 Blazer Silverado 6.2 4" lift 35"s
-'95 Ext. Cab Shorty 4" Tuff Country rolling 35" M/T's
-'83 Monte Carlo T-Tops. 126,500 Original Miles
-LATER
I would rather push a Chevy then drive a ford!!
Hoods69BadBowTie is offline   Reply With Quote
Old 03-05-2005, 12:00 AM   #8
79C10
Registered User
 
Join Date: Jan 2005
Location: Northern Vermont
Posts: 159
did you check the carb gasket?

-Levi
79C10 is offline   Reply With Quote
Old 03-05-2005, 01:44 AM   #9
jermasaurus
Registered User
 
jermasaurus's Avatar
 
Join Date: Dec 2004
Location: New Lenox, IL
Posts: 442
I actually had my Q-Jet backfiring on me when it was waayyyy too rich just before I took it off. It was so rich that it was fouling plugs to the point where they wouldn't even fire within a week!! And it also lacked power like you say. But Yeah, It is most often like everyone else said-Lean or maybe a Vacuum leak. I have also heard of ignition modules doing that, but I'm not sure what setup you have.
jermasaurus is offline   Reply With Quote
Reply

Bookmarks


Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -4. The time now is 03:19 PM.


Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
Copyright 1997-2022 67-72chevytrucks.com