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Old 02-07-2013, 01:28 AM
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Back firing

I have a 1985 gmc swb with a 350. I have done some changing around tho. I have used a 1987 chevy block and put a inline fuel pump along with a regulated for the fuel system and ran a carb on it. The problem I am having is it wants to backfire threw the tail pipe. I have tried to set my timing and as far as ik I have it set but it keeps doing it. I don't have any other ideas why maybe it would. Maybe the carb? Overload on fuel? Any ideas?

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Old 02-07-2013, 01:33 AM
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You'll have to give more detail on tried to set your timing. Did you use a timing light? If so what did you set it too? What distributor are you using?
What's the fuel pressure? How many miles are on the engine? Did the problem start out of no where or did it start after you changed something?
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Old 02-07-2013, 01:38 AM
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No timing light. I am using a distributer with the internal coil, not sure what it is actually called. I have been running it at 4lbs. The truck was running great And the problem came out of no where. It started by the truck cutting out and finally dieing. I replaced the coil, had a broken wire. After I replace it I can get it to start but still back fires.
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Old 02-07-2013, 01:42 AM
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You must time it with a timing light. Don't never attempt to time one "by ear"
as you can lead it into detonation which creates engine failure. When you replaced the coil did you remove the spark plug wires?
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Old 02-07-2013, 01:43 AM
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Well I took the plus off the cap to replace the coil.
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Old 02-07-2013, 01:53 AM
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Then you should check to make sure you got the firing order correct.
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Old 02-07-2013, 01:34 PM
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I agree. Number 5 and 7 are right next to each other on the cap and the engine will run (poorly) if these two are swapped w/each other.

Firing order:

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Old 02-07-2013, 01:49 PM
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Ill check that
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