Last summer I replaced the head on my blacktop CA20 with a reconditioned head from a pro headshop. Since then I've had an unusual issue with the engine dying, at cold engine temp, when I brake hard enough to really shift the weight forward.
Scenario:
Start up in the garage and roll down the street toward stop sign. If I drive up like normal and step on the brakes, RMPs drop to zero and kill the engine. If I disengage the clutch and roll up to the stop and brake lightly, stopping slowly, then there's no problem. Usually by the time the engine has warmed to temp the issue goes away, usually.
Additional factors:
Many times if I turn on the blower the RPMs increase just enough to sidestep this issue, usually.
Idle is often irregular regardless of engine temp, even from one stop to the next. It may vary as much as 500 RMP.
What really puzzles me is the braking momentum. It's clear that when weight is shifted forward the engine has a much higher propensity to stall.
I simply haven't been able to puzzle my way through this one. Has anyone had a similar issue? Does anyone have insight to the cause?