I've got a '78 F-100 6cyl 4 speed.

Runs great! Except after about 15 minutes now it gradually starts dying. It's willing to accept less and less throttle before just not running aside from at idle after maybe 20-25 minutes. It'll always idle great it seems, but it just won't run or respond to the throttle at all. if I let it cool off (usually till the next day) it'll run great again for 15-20 minutes before it starts running poorly.

I changed the fuel pump since I noticed the old one was starting to leak, but that didn't help. Fuel filter is new. I took the top off the carb and everything looks clean and shiny (I rebuilt the carb in the winter so this doesn't surprise me).

I've been told my symptoms sound like a duraspark issue - is there any way to see if this is the case? I'm not sure how to test it especially since it only has the issue when it's been running for a while.

I've also got an MSD unit laying around I could throw in to replace the unit if that's possible. MSD 6A.

 

Hmm, is the choke sticking?

Adrianspeeder