I have had gas engines run great on the test stand while I ran them and broke them in some. Then I stopped running it and finished building a airplane and mounting the engine in it. A week later I take it to the flying field and discover, much to my dismay, that the engine won't run right. I rebuild the carb and it works great once again. I have had other engines run Ok for several weeks and then develop problems requiring a carb rebuild too.

I also suspect we have quite a few fake or counterfeit Walbro Rebuild kits out there in the world too. Such that the diaphragms don't last very long. Then you get lucky and find a real set and the parts last for ages without going bad.

My old crappy Poulan weed trimmer is still going strong after several years of use and abuse. it does take a lot of pulls to get it going after a long layover though. My cheap chain saw is similar and still seems to work irrespective of the treatment or lack of treatment it gets too. So sometimes I wonder if the RC engine companies are getting crappy rubber parts inside of the carbs versus what comes with the utility engines.