backfiring issues
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backfiring issues
i just got an 83 f250 4 wheel drive 351 4 speed. when i bought it wouldnt hardly run a lick the carb that was on it was done. i put on another one i had in the garage and it runs good runs smooth and everything. but when im drivin and i let out of it it will back fire i have tried everything i know to fix it. i cut the old glass packs off it put 2 brand new flowmasters on it figured with the new mufflers puttin back pressure on it like it should have it would get rid of it. i tried messin with the timing timin i know is set right. it dont turn over slow at all it fires right up just like it should. it idles smooth runs good has plenty of power like it should. i have checked the all the wires there aint none burnt or anything. i put a new fuel filter on it its a clear plastic one so i could see how much fuel she is gettin and there aint much fuel goes through that filter at all. i dont know if the fuel pump is weak or somethin. or if its puttin fuel somewhere else. idk i need some help on fixin this. if let out of the throttle real slow it wont back fire real loud it just pops a little bit.
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Joined: Jan 2001
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From: Virginia
It's running too rich. The backfire is raw fuel getting to the hot exhaust and lighting off. I don't know what carb you put on it, but it may have a blown powervalve or some other problem. Does it smell a little rich when it's setting there idling?
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Joined: Jul 2010
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From: Northeast, OK
Or the idle is way too rich. Try running the idle screws in 1/8 to 1/4 turn from max idle RPM.
And, something in the back of my mind tells me I've seen this associated with where the vacuum advance is connected. But, I can't remember exactly what it was. Seems like it was using manifold vacuum for the advance instead of ported vacuum, although I can't tell you why that would make a difference. In fact, were I to think through it logically I would say it would be the other way 'round as manifold vacuum would cause you to have to close the throttle blades further at idle. Anyway, there's something way back in my memory about that.
And, something in the back of my mind tells me I've seen this associated with where the vacuum advance is connected. But, I can't remember exactly what it was. Seems like it was using manifold vacuum for the advance instead of ported vacuum, although I can't tell you why that would make a difference. In fact, were I to think through it logically I would say it would be the other way 'round as manifold vacuum would cause you to have to close the throttle blades further at idle. Anyway, there's something way back in my memory about that.
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i got a 2 barrel holley on it for now. i got a 4 barrel edelbrock im going to put on it but i gotta get an intake the take i got off of one of my old trucks i was gonna put on this one is cracked. as far as i know there aint no way to adjust a holley like an edelbrock. and i got my idle screw backed off pretty far it idles at about 600 to 650 rpm and no it dont smell like its runnin rich idlin. and i was out messin with it earlier this afternoon during halftime and pullin the vacum line off the vacum advance on the distributor it didnt change it at all. like it wasnt getting vacum or the the vacum advance on the distributor is bad. it looks like its the original i put a new cap and rotor on it also.
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