Hi all.
I recently purchased a 1970 F100 2wd.
I began driving the truck as a daily driver about 3 weeks ago and noticed it was developing a pronounced miss under certain conditions such as driving uphill and changing speeds on the freeway.
Since the truck had a fairly pronounced oil leak coming from the timing cover, i thought that would be a good place to start (kill two birds with one stone) sure enough, the chain was severely stretched with over an inch of play. After changing the chain and gears, cap, rotor, plug wires and cleaning/gaping the points and spark plugs it ran great-for a week.
Upon driving to work one morning, after the engine had been running for more than a half hour, the engine began sputtering and back-firing to the point that i had to pull off the road. After towing it home, i discovered that the engine will idle more or less fine but when i put it in gear to move it starts again with the backfire/sputter thing.
I have an original '70 302 with high miles (no knocks, taps or pings though) a stock Autolite 2bbl, stock ignition with the exception of MSD coil, dual exhaust with factory manifolds.
Another thing worth mentioning is that it puffs white smoke at start-up which i know usually means coolant but it is only at start up and the radiator has only lost a small amount of coolant if any.
Anybody had the same experience or any ideas?
Any help would be greatly appreciated as the truck is a strong looker and i would like to make it a strong RUNNER!

 

My 71 with a 360 had a large vacuum hose come off the back of the carb. Because the idle mix was too rich, this caused the engine to idle at a higher speed, then when put in gear to lean out and die. So a good starting point may be to check your vacuum lines.