RE: Near miss disaster 50cc
Vent/pressure line?? Never seen one on a gasser. Just wondering? What engine was that?
My Brison 2.4 was doing about the same thing, ran great on the ground but right after take off it went south on me. I fiddled with it for a long time but due to the needle placement I couldn't tune it while it was running, needles very close to the prop. Even with a tach I couldn't find the magic spot so I risked some of my favorite parts and got it running and found my high end was way off. They tune like any other engine, I brought it up to the highest RPM at full throttle then backed off a few hundred then adjusted the low end until it transitioned correctly. That was almost the last time I have ever touched the needles on that engine and it runs great.
I just tried some different props a couple of weeks ago and tuned it with a tach, moved the needles then started it up and took readings until I got it correctly where I wanted it. My have something to do with the engine being broken in now because it was easy this time?
The gas engine forum is really the place to ask. That way you can find people with the same engine to help you out.