So i had some pretty messed up wire on my engine harness, I fixed all that up along with a carb rebuild, repainting and cleaning the fuel tank.

Now im onto the issue of a light backfire every few seconds. It is irattic and goes away at times, maybe during higher then idle RPM's the sound is muffled.

But im wondering if any of you have expirenced this? The timing seems to be dead on 8*btdc, Is it possible my timing chain isnt set properly?

Could a valve lash adjustment be part of the issue?

maybe just dizzy points?

I will be checking the header for a possible crack this evening, Im just hoping for some key words of advise.

thank!

 

so my point gap was around 1/8th of an inch

i tighten it up to .45 mm

anyone know what the gap is supposed to be on a 78 20r?

i could only find info on the years 75-77 and then missing information from 78-80's

The motor still sputters, I notice my carb isnt opening the 2nd barrel at all. anyone know poss why? I think i may need a PCV/EGR system rebuild ****ty...

 

I would think spark gap would be relatively the same from a 77 to your 78 or try info for the 81 up. My gap is .31 but I have trucks in the 90's with completely diff motor so yah??? Depending on what kinda carb you have stock or aftermarket maybe your butterfly is just stock and needs some greasing up. Maybe your linkage isnt snapping properly along with throttle??

 

air injection valve was my issue my truck is a 79 20r and it had a light backfire on decal I capped the two small vac lines to the valve problem went away funny thing they were plugged off when I bought it I plugged them in and it was fine for the first month then it started popping on decal I cleaned and adjusted carb and no change un plugged and capped lines all was fine after that give it a try it might help