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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: pedigo78 on August 29, 2013, 07:06:37 pm
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well the other day i started big blue up and it started backfiring, and idling rough. I though it was the gas i had just put in it cause this has never happened before. anyway went put fresh gas in, drove it around, come close to dying when stopped, kinda smooths out at at about 30 mph, backfires more and more as speed increases. although power doesn't seem to be lost. check cap and rotor, cap was lose, tighten it back on, checked plugs wires, changed plugs. check dist. hold down bracket it was tight so timing has moved. carb cleaner down the carb. and now have a new cap and rotor on order. what else could it be
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Has it been sitting for a while? Carb may need to be cleaned out of varnished fuel. Did the fuel smell stale?
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no field in smell bad I drove about 2 weeks ago um I'm driving about every two weeks or so get out there started driving around.yeah like I said I put brand new plugs in it check the wires ever find a distributor cap was up a little bit so I went ahead ordered one I put that on to that does the trick.none of the tables have been messed with so I know they're the right firing order I just weird to start I'll send backfired
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Float bowl valve stuck open? Can happen with sitting, right? If the engine was turned off when the valve was open.
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Sounds ignition related. Are any of your wires touching the engine block or ground? While it's dark go start it up and check for arcing from plug wires.
What's under the hood??? If you have to ask maybe we shouldn't race...
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ill double check everything again. should get the parts in the mail soon. either way it need new plugs, cap and rotor
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might of damaged something in the cap and rotor from it being lose
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What kind of carb? A backfire could have been caused by many things. Maybe you fixed the original problem with all the parts you replaced, but now have a new problem with your carburetor because the motor backfired.
A similar thing happened to me recently: I replaced my intake manifold, along with a brand new carburetor and distributor. When I put it all together the timing was off, also my carb spacer had a big leak. So it backfired. I fixed the timing and spacer issues, but then my power valve in the 650 Holley spread bore was blown.
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dang I hope it isn't all that. I am actually getting ready to sell the truck. lol
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if it back fires out the tail pipe your good out the carb is when you can blow the power valve
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ok, so yeah It is coming from the tail pipe, I was actually leaning over the motor checking the carb and there was no backfire from the carb, it was all coming from the tail pipe. So that means my carb should be good?
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Did you check the wires? Look for arc
What's under the hood??? If you have to ask maybe we shouldn't race...
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No I didnt get a chance.
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just run the engine and run your hand down each spark plug wire (http://www.naioa.com/v2/modules/Forums/images/smiles/lol_hitting.gif)
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Don't forget to get a video of doing the last suggestion.
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lol
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No I didnt get a chance.
Any luck? All you have to do is visually check for the spark plug wires leaking voltage (aching) to any metal parts
What's under the hood??? If you have to ask maybe we shouldn't race...
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ok, couldn't do it at night like you said 454Man but I didn't start it and physical touch each wire, and nothing happened. So I finally got a tracking number for my cap and rotor should be here weds. Other than that, im out of ideas my mechanical skills are about ran out. I don't know shoot about timing although I would see why that is bad all the sudden, and don't know anything about carbs either. And this is all bad timing as well cause I am actually in the middle of selling the truck. And It would be junky to sell a guy a truck that is backfiring
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The last thing you need to do is listen to someone that's says touch a possible leaking voltage plug wire. If you got hurt it'd not be on me! Do you have an ohm meter? Pop the hood at night, let the truck run while watching for plug wires aching to a ground even at the boots...
What's under the hood??? If you have to ask maybe we shouldn't race...
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Alright I'll try it this evening.
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lol sorry ped i didnt mean for you to take my post seriously. that was the point of the smelly after the post. but like said the best way to see is if you run the engine at night and it looks like fire works.
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well either way, all is good. just checked it and no sparks. This is what I have realized. no hard starting at all, at idle it will backfire, apply a little gas and it goes away, so when I pull up at stop sign I apply brake and gas to keep the rpms up. Although while driving on some back roads at about 35 mph it goes away, but when I would try to speed up, it would start up again. I do have a new MSD cap and rotor coming in soon. Should I get new wires, already did the plugs? I have a guy waiting to buy truck, trying to get it taken care of before sell. don't want to discount the price for him. lol, by the way guys thanks for the help so much
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Get new wires
What's under the hood??? If you have to ask maybe we shouldn't race...
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Does it backfire when a load is placed on the engine or does it try to die as well? I recently had a power demand issue with my 305 85 c10 and found out after pulling out my hair it was a bad vacuum advance canister? 15.00$ fix and not all that bad to do if you know the workings of that HEI system. Also, a back fire could possibly indicate a timing issue if it was firing out of the carb, but you mentioned that it was only out of the tailpipe correct?
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Check your initial timing with a timing light, you may have it retarded.
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yeah, mine is a mechanical advance, but I got a guy coming tomorrow that's a little better than me and this stuff. So hopefully we can take care of it
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well, just as I thought, it was bad gas. I guess me adding gas from another station wasn't enough. Add some SeaFoam Good as new. Thanks for all the help. Thought the new plugs, cap and rotor isn't a bad thing.
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Well i have not been on in awhile due to work, but it turns out it was not the gas. When truck is running at a high idle it will not backfire, although at idle or low rpms it will. I fixed my exhaust leak, replaced the plugs and bought a new cap and rotor. Ill get new wires on payday and put it all on. Anyway, just thought I would inform you all of whats new. THanks