On Wednesday, February 3, 2021 at 5:10:11 PM UTC-6, Mark Mocho wrote:
Not to hijack the thread, but in response to the reliability issue of two-stroke engines, the primary culprit seems to be the different altitudes at which the engine is supposed to start and operate. The fuel/oil/air mixture has to be within certain parameters for decent running and starting reliability. An increase in altitude (or high density altitude conditions) reduces the amount of available oxygen, which contributes to fouling the spark plugs. I used to ride the Yamaha RD-350 and TZ-250 motorcycles from Albuquerque (elevation ~5,500 ft. MSL) up to Sandia Crest (10,678 ft. MSL) and used to have to stop and adjust the needles in the carburetors four times on the way up and four times on the way down or risk plug fouling or overheating and possibly seizing the engine. About a 1,000 ft. change in altitude was all it took to affect the performance and reliability. Newer two-stroke engines with more sophisticated fuel injection systems seem to be much more reliable in motorgliders.

Oh, that brings back memories. I too rode an RD-350 (voted as the "Bike most likely to lose you your driver's license"). Even tried production class road racing on it a couple times (scary). Had the same experience as you with riding in the mountains. Used to stop on the way up to Deal's Gap and drop the carb needles a notch. Put 38,000 miles on the bike. Never failed to start and run. Stopped being scooter trash and became glider trash, but still have that bike (mothballed since 1981).