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Discussion Starter · #1 ·
I have a 79 f250 with a 300 6 an a 4 speed, I got this truck a while ago and it sat for 6-8 months before i put it on the road last month. It ran great when i got it, but now it will not run for ****, especialy on damp days. What it does is this, It will run fine, then stumble and buck like there is water in the gas, then it will pick up and fire and blows the muffler apart
I have rebiult the carb and flushed the fuel system so i know there is not water in the gas. When it runs it will run well, then it does this. I have replaced the Coil, The inductive pickup, the Dura-crap box on the fender, cap upper and lower rotor and wires/plugs. It still will not run well, the only two things i have not replaced the six eared trigger for the sensor and checked the leads comeing from the ignition switch. I have even gone over the engine harness with an Ohm meter and checked for hard spots in the wire, everything looks good. This thing is realy getting ther best of me. any help would be appreciated. Convince me i like this system before i rip it out and go back to points.
 

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Double check the harness for previous repairs. My dads 75 did this when an old twist and tape wire repair got signifigantly corroded. Harness looked factory, only way to find it is to start unraveling tape. On the plus side, you get to put all new tape on. If that doesnt turn up anything, Id see about replacing the dizzy. Only about 35 or 40 at Autozone, and fairly easy swap. I've seen em do that same problem on a 400 in an old work truck, replaced everything but the dizzy, still popped and died, replaced the dizzy, bingo, smooth as a babies ass.
 

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The prob with the dizzy is the permanent magents loose their magnetism when hot (on a bad dizzy) Can't see it, dont even really know how to test it, but it can cause the problems your describing. If nuthin else has worked give it a shot.
 

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Discussion Starter · #6 ·
Well,
More to it today. The ambient temp here is about 40-50 degrees Humidity aboyt 70-80%. Today i found a ripped accelerator pump diagphram in the carb by the way it is a carter 1bbl YF. I replaced that all looks clean and shiny. I set the carb, and it ran great. so i figure i have fixed it. on my way to the beer store tonight the engine was dead cold it is about 50F out and drizzling. i fire it up, runs and idels well, but when i let out the clutch, no matter how much i burn it or how much gas i give it if falls on it's face, but does not die. it will chug and fart, but not stall. Aftre some heavy revving i get it to wheeze out of the driveway. It will now go but it misfires like a bastard. then it starts to run fine, drives well, i take a corner and it is back to chugging and popping, now and then a few backfires. I limp it into a parking lot and pop the hood. there is nothing arcing. I fiddle withy the idle a bit but not much happend it misses along at about 200 rpm, Idle is set at 650 or so. I sit in the lot and rev the piss outa it (im kinda pissed by now.) and fignaly it starts to run right. I drive about 3.5 miles make a stop and leave it running. I start to drive home. it runs well about half way it starts to misfire, it runs misfireing for about a mile. then it does the now famous muffler explosion (The guys at the return line in autozone love me
), aftre this it runs with a misfire all the way home. I haqve also checked the fuel pressure while driving, it is a steady 5-6 psi. Any ideas woulod be appreciated.
 

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Discussion Starter · #8 ·
I fignaly figgerd it out today. I had a bad ignition module out of the box from Autozone. those guys had a realy bad day when they told me I could not return a 3 day old Duraspark box.
 
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