07-16-2007, 08:28 PM | #1 |
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Backfiring
My truck is starting up and it hesitats when starting. Once it goes it runs great above 2500 rpms but bellow that it starts spitting and sputtering and backfires. Any ideas? Also the engine will not idle if you let off the gas the engine dies out
Last edited by pyro883; 07-16-2007 at 08:33 PM. |
07-16-2007, 08:37 PM | #2 |
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Re: Backfiring
Check the timing. Is it backfiring through the carb or exhaust?
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07-16-2007, 08:38 PM | #3 |
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Re: Backfiring
through the carb. I cant even get the truck to idle to time it.
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07-16-2007, 08:51 PM | #4 |
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Re: Backfiring
Pull plug wires off one at a time. Could be an intake valve?
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07-16-2007, 09:36 PM | #5 |
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Re: Backfiring
1. I'd check timing, by hand if not by light.
2. I'd consider the age/condition of the carb. Is this an existing problem that got worse, or a new problem on a newer setup?
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07-16-2007, 10:31 PM | #6 |
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Re: Backfiring
Carb flooding. Do you see black smoke?
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07-17-2007, 06:39 AM | #7 |
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Re: Backfiring
Plug wires crossed?
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07-17-2007, 07:23 AM | #8 |
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Re: Backfiring
I would check timing, Also inspect the cap and rotor for cracks or excessive wear. Check and make sure your idle is right, You can also Try retarding your timing by hand & Ear.
You can also pull your plugs to help let you know if you're running a little too rich or lean (Grey / Ash color Lean, Black or sometimes gasoline smell is Rich, Tan is just right), and make sure your Firing order is right (more then likely it is but just in case.) Float Level Too High? That should help, Need more info on the truck to get a better idea on whats going on. Sounds like the timing is too far advanced though and the idle might be off a bit, More info would help though. Last edited by Pumped 68; 07-17-2007 at 07:25 AM. |
07-17-2007, 08:38 AM | #9 |
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Re: Backfiring
Sound like one of a few things. The timing is too far advanced,the chain is streched, cam is going flat, or the wires are in the wrong places. Firing order is 1-8-4-3-6-5-7-2 clockwise. Good Luck. Keep us posted.
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07-17-2007, 08:51 AM | #10 |
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Re: Backfiring
Backfireing through the carb is a lean condition or timing is late. Advance the timing not retard it.
Make sure all ignition parts are good and carb accelerator pump is working. I would start there first.
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07-17-2007, 09:40 AM | #11 |
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Re: Backfiring
Agreed that job 1 is timing. If you can't get the truck to idle, you can statically set the timing by positioning the engine at 8-12 degrees BTDC and pointing the rotor exactly at the #1 tower.
If you can't get it to idle, I'd also take a hard look for vacuum leaks. |
07-17-2007, 07:23 PM | #12 |
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Re: Backfiring
Well I advanced the distributor to get the best time i could get with just sound. Now its no longer back firing. I also think I found a vaccum leak there are 2 black gaskets on the carburator, and I sprayed starter fluid and it reved up when i sprayed it along the gaskets. So I went to autozone and they dont have any gaskets for it saying it was part of a rebuild kit. Dont know if there is any truth to this. Do any of you guys know and if so where do you get them at. I belive I have quadrajet carb. Thanks for any help.
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07-17-2007, 08:02 PM | #13 |
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Re: Backfiring
Just a reminder that your timing is almost certainly too far advanced at this point.
They're likely right about the gaskets; the rebuild kit should be fairly cheap... |
07-17-2007, 08:12 PM | #14 |
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Re: Backfiring
after all that i have seen it sounds like your timing is a full 180 out and a new set of plugs is recomended. you should be able to tell if u have a quadrajet, its an almost perfect square and looks like no other carb out there.
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07-17-2007, 08:55 PM | #15 |
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Re: Backfiring
Sounds like a vacuum leak to me.
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07-17-2007, 09:02 PM | #16 |
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Re: Backfiring
I can't see how it's 180 out if it's running smooth above 2500 RPM...
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07-17-2007, 09:03 PM | #17 |
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Re: Backfiring
Well here is pictures of the carb that I have. Maybe someone can help with me with what kind it is. I am not sure I am new and dumb to all of this.
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07-17-2007, 09:23 PM | #18 | |
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Re: Backfiring
Quote:
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07-17-2007, 09:36 PM | #19 |
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Re: Backfiring
anybody know where i could get a rebuild for it?
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07-17-2007, 10:26 PM | #20 |
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Re: Backfiring
Looking at that picture, the first thing I notice is that the clamp is missing from the PCV hose where it fits on the carb.That is the larger black hose that goes into the front center of the carb and from there to the PVC valve in the left valve cover. Chech those connections and add a clamp. If the hose is hardened where it fits,replace it! Pull the PVC valve out and shake it to see if it "rattles" (it should,if not REPLACE IT!). Spraying starer fluid around the carb will always cause an increase in RPM because it will be sucked into the carb,it's kind of a tricky test. If you had the air cleaner on and the gaskets under that were good,then the test would be more meaningful as the spray would be less likely to find it's way into the air-cleaner intake.
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07-18-2007, 12:08 AM | #21 |
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Re: Backfiring
Wow, what was I thinking!? I was meaning retarded and put it adavanced! Now I am retarded! Sorry!
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07-18-2007, 12:09 AM | #22 |
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Re: Backfiring
I had a backfiring problem like you, and it was because of a lean condition (vacuum leak).
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07-18-2007, 12:40 PM | #23 |
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Re: Backfiring
By the look of the carb in the pic, it looks like it's a recent rebuild. Check the accelerator pump for proper operation. Engine off, look down the front 2 barrels while slowly opening throttle all the way open. You should see a continuous stream of gas shooting into each front barrel. It's real common for rebuilds to have that circuit not working right.
That won't affect idle, however. Try holding your hand over the front barrels and see it it helps it to idle. It it helps, possible idle mixture problem or could have a problem with the idle circuits in the carb.
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07-18-2007, 02:02 PM | #24 |
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Re: Backfiring
vaccuuum leaak
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07-18-2007, 02:30 PM | #25 | |
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Re: Backfiring
Quote:
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