I ve got an 81 4x4 rebuilt 21RU 32/36 weber and tri y header. a week ago it started to act up. I can take off and it runs great til I hit 4,000 RPMs then it acts like its runnin out of gas. I ve replaced the fuel pump 3 times, two coils, cleaned the carb and all new fuel lines, rubber and steal, and still cuts out at 4 grand.

 

Maybe someone put a governer on it...

But seriously...I don't know much about that engine. I wonder if the carb is incorrectly jetted? Or out of adjustment. I'm sure when you were working with all the fuel stuff you replaced the filter, including the one in the tank.

 

yep new filters and it had been runnig great for months before this. gonna pull the carb again 2maro and go through it

 

 

Buy an hour at/on the local dyno. This will give you info on the fuel mixture/ AFR ratio. They likely have the hardware to monitor timing (oscilloscope) and can tell you if there is something wrong with the vacuum advance ect.

PS, just saw this is a three year old post ffs, ug.