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The particulars...stock 302, recently put all new seals/gaskets, replaced timing chain and oil pump and generally cleaned up. Was and is running really well, but has developed a strange performance characteristic. I have to cross the mountain to work each day, and if I try to accelerate to pass a slowpoke while going uphill, it seems to bog down...will not accelerate and sometimes sounds like small backfires. Occasionally I've experienced rough idle as well. It seems that the problem only occurs in third gear (C-4), but it also doesn't seem to be downshifting properly either at this point. It does seem to do it also if I try to accelerate on even ground above 70 MPH. That's about all I can think of at this point...any ideas? All input is appreciated.

Thanks,

Bill
 

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Vacuum leak? Timing too advanced? Is there any pinging? Clogged fuel filter?
 

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When I was a very young pup, Mom and Dad bought a 66 Mercury Montclaire new, which developed this same problem. I recall sitting in the backseat, wide eyed, as a garage mechanic took it on a test run at triple digit speeds. The final solution was bizarre. There was a buncha crud which was clogging the fuel intake in the gas tank, caused by a leak at the dealer which they repaired by brazing. The car couldn't get enough gas under high load conditions. Perhaps obtain a fuel pressure gauge, disconnect the carb from the fuel line, and see how much pressure you have at idle until the fuel bowl empties. If this shows no problem, approach it from a load standpoint. I saw this once with a bad coil, where the engine sputtered under a load.
 

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I had this exact same problem a while ago, and I never really solved it. It turned out to be that the distributor cap was crossfiring inside and making carbon lines. It eventually got so bad it happened continuously until the cap was replaced (although it came back again). My solution was a new 351w, so I don't really know what caused the problem. I was thinking about buying one of those late model widepost distributor kits. Hope it helps.

~Brett
 
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