91 gmc part throttle issue

[rusted40]

I recently bought (cheap) a 91 c1500 5.7 that the PO was having part throttle stumble.

So being a hoarder of SBC parts I figured I'd throwback to a carb-mechanical pump and HEI, no problem.

The problem went away except an intermittent cranking problem hot or cold.

So I dig deeper into my pile of better parts and switch from HEI to a magnetic MSD, 6A and blaster coil, all hooked up correctly, no bubba.

Now the original problem of bucking at part throttle is back, it runs great at WOT.
no cranking problems.

The only thing common is the pink wire I used to feed the HEI and to activate the MSD box.
is there something else to the pink wire or is it just 12v?

 

[dylan94sierra]

I had this problem where it was sort of like a bucking under slight acceleration. There was also a very slight miss in the idle. Turns out one of my plug wires was sitting on my exhaust manifolds and burnt through the casing and the metal on metal caused it. As soon as I took it off it ran much better and fixed the problem

 

[rusted40]

vacuum advance was bad