Don't know if this is electrical or Carb, my 390 in my 73 f100 4x runs the best before it warms up, after it is at operating temp for some time, and especially if i am driving in town for a while it starts missing on compression and when i'm not accelerating at least moderatly. At its worst it also cuts out and hardly runs when i depress the pedal. If i park and let it cool from operating temp some its OK again, but still misses as described above. I believe its running somewhat rich as it pots on compession, but no back fire. Is this a vapor lock? I'm the original owner and this is a faily new issue to me. I also am thinking the plug wires may be breaking down, as i had a bad miss and found a loose end, they are 10 to 15yrs old. Any Thoughts on this would be appreciated, thanks.

 

Sounds like you have some basic problems to fix before trying to determine if the carb has a problem. First give the truck a complete tune up including plugs and wires. Check engine vacuum at idle and make sure you are getting at least 18 - 20 inches at idle in neutral. Repair any vacuum line problems and verify the engine timing is correct before messing with the carburetor. Also, how many miles on the engine, especially the timing chain and gears?

John

 

Eng was rebuilt at 92k, new crank and rods for current 390 that has 89K now, Ok thanks, your right to start at the beginning, and i'll check them. In between rain I have only checked dwell. I have a vac gauge mounted so the vac is good. I'll check those componets and test cables, I have an old Wards analizer that will check the plug wires but believe they will porbably only not check out bad if at all when they are hot.

The engine runs strong still, way better than original, no oil burn no signs of wear. I never thought it would last this long because for whatever reason it has always run hot at idle and with load or hills., but i have always managed it, which has been pretty easy since I don't city drive.

 

Possible vapor lock problem?