Because you've mentioned that it's back firing thru the carburetor and getting gradually
more sluggish, the first place that I'd look is to the timing. Sounds to me like the timing
may have slipped for some reason.

Unless someone has been in there and tried to improperly adjust the valves three years or
more running on a valve adjustment is just going to loosen up the clearance, which
simply means the valve is not going to open fully. Even if a lock nut came loose the
clearance is only going to get greater not tighter. On the other hand, it’s possible you
might have a sticking or burnt valve or some carbon build up under a valve holding it
open. If timing it back to the "Ball" doesn't cure the problem then a compression test
would be my next step to see if the valve train is still on track.

Oh, and once you make sure the timing is correct and the valve train isn’t your trouble,
then it sure wouldn't hurt to get a fuel filter in the system and rebuild the carburetor
if it hasn't been serviced in a while. A fuel filter was a good idea when these trucks were
now and an absolute necessity now that they are old.

Denny Graham
Sandwich, IL

Last edited by Denny Graham; 01/02/2012 1:34 PM.
Denny G
Sandwich, IL