I had a 120 Lehman that drove me crazy with a capricious stall - turned out to be a little bitty screw on the injection pump. I was in despair having traced checked everything and suddenly a tiny bubble formed and popped on this screw. An "aha" moment! I removed the screw, annealed the tiny copper washer and screwed it down again, never another stall problem. Good luck finding yours, it's an air leak 100%.
"...Tongue tied and twisted, just an earthbound misfit..."