backfiring gas from carberator? help?

randal

Golden Member
Jun 3, 2001
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Hey everyone,
I have a 1982 toyota 4x4 pickup running a stock 22r (well, headers). The other day I was downtown doing maybe 20mph and all of a sudden my engine bogged down and wanted to die. Pulled over and she wouldn't start and it smelled like gas. Waited about 15 minutes, turned her over and idled her home 10 blocks.

Well, I got to look at her this past weekend and this is the situation: the engine idles a little rough until it warms up, at which point it idles okay. If I slowly rev up the engine (while in neutral, no load), it revs up with no problem. If I floor the gas, it makes a rather loud, very fast kind of "chuff" sound that comes out of the carberator on the left hand side (right side is choke, correct?). When I smell it, it smells very much like gas, and it is usually visible as it comes out of the carb.

I thought that maybe I wasn't burning all the gas in the cylinders, so I replaced my spark plugs & rotor cap and checked the distributor timing -- everything was in order. I checked the PCV valve, and it seems like it's in okay shape (it rattles when shook lightly). Vacuum advance is working perfectly, as is every other function of the car.

Any idea why my truck is "backfiring" gas out of the carb? If so, how do I fix it?

Thanks!
randal
 

Evadman

Administrator Emeritus<br>Elite Member
Feb 18, 2001
30,990
5
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sounds like the accelerator pump is having problems. When you stomp on the gas in a carbed vehicle, tha vacuum disapears. there is a accelerator pump that injects extra fuel in during this time. the diaphram could be ruptured, or the oriface that the fuel comes out of is pointed the wrong way.

even if I am wrong, this is certainly a carb problem. fuel goes down, not up :) Time for a carb rebuild. You may also have timing issues.
 

skyking

Lifer
Nov 21, 2001
22,009
4,775
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sticking intake valve, timing way off, distributor problem (spark "looks" OK but is all over the place sometimes), vacuum leak.
Those are causes for the symptoms you describe that I have seen.
 

randal

Golden Member
Jun 3, 2001
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even if I am wrong, this is certainly a carb problem. fuel goes down, not up :) Time for a carb rebuild.
That's what I was thinking ... I know my vacuum system is in good shape because the timing is correct, even when it's supposed to be advancing. I was also thinking that if the distributor is toast, wouldn't it idle like crap? And not run smoothly when rev'd up?

The local Toyota shop wants $300 for a new carb + 4 hours labor ... $580 for a carb!? $26.50 at autozone is fine -- I just wanted to get some more opinions before I go buy a carb rebuild kit and waste a saturday ...

randal
 

Evadman

Administrator Emeritus<br>Elite Member
Feb 18, 2001
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cam timing could be too. If you jumped a tooth or 2. It did happen suddenly. *shrugs*
 

randal

Golden Member
Jun 3, 2001
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I made sure that the choke opens and closes correctly -- it does, and does the fast idle cam works correctly as well.

I was thinking that if the timing chain hopped a link that it would run very poorly all over the rpm range, warm or cold. That's why I was thinking it was a carb issue ... (am i mistaken? because getting at my timing chain is a *huge* undertaking -- cheaper to sell it)

randal
 

Evadman

Administrator Emeritus<br>Elite Member
Feb 18, 2001
30,990
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I was thinking that if the timing chain hopped a link that it would run very poorly all over the rpm range, warm or cold. That's why I was thinking it was a carb issue ... (am i mistaken? because getting at my timing chain is a *huge* undertaking -- cheaper to sell it)

randal


I am just tossing stuff out that may cause the problem. I am sure that Roger will come in here and set up all straight with: what happened, why it happened, where to get the parts to fix it, the cost of the parts, and how to fix it :)
 

farmercal

Golden Member
Mar 23, 2000
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About 12 years ago I had a 82 Toyota Corrolla and rebuilt the carburator. The kit I got came with a diaphram piece that had been worn out inside my carburator and when I finished the rebuild the car ran like a champ again. That part might be what is causing your problem (don't know). You are right about buying a rebuilt (it is expensive) that is why I rebuilt mine. I had over 200K when a drunk driver pulled out in front of me and destroyed "Bama" and I would still be driving her today if the accident hadn't occured. Yes, I named my car but when you drive a card for 16 years and it doesn't use or lose a drop of oil between changes you get kind of attached and I haven't had a card like that since.
 

Ornery

Lifer
Oct 9, 1999
20,022
17
81
First thing that came to my mind was timing chain/belt. After thinking about it, I'm wondering about the throttle position sensor, or something along those lines. Anymore, I just take mine to my mechanic. If I know what the problem is, I'll have at it. Otherwise, I'll give the poor guy some work. He says since this 0% interest for new cars took off, he's got a hell of a lot less business.