[Mike Fowke]

Originally Posted by lust4speed

Is it WOT or higher RPM breakup? While they usually occur together, if it is RPM related a weak spring could be allowing lifter to not follow the ramp and also contribute to some additional wear on the lobe. Valve not closing would definitely promote backfiring.

It happens consistently at WOT, under load, at higher RPM. For example, punch it in 1st or 2nd at low speed, it will accelerate, reach a certain RPM and break up. It doesn't nose over or die. It just starts backfiring. If I build some speed and ease into WOT it usually takes off with no issue, and I can wind it up. So, I think it's load dependent and not RPM.

If the problem persists when I get it back together, I'll post a video. I'll also verify the RPM where it breaks up and if I can reach the same RPM easing into WOT.

The machine shop hasn't returned my call yet about measuring the springs.