I have a 2-stroke Shindaiwa backpack blower that has been trouble free for ten plus years. This summer it has been harder and harder to start which turned out to be loose carburetor bolts and some pretty worn out gaskets.
I sealed the carb up and it starts and runs great for 15 minutes or so. After that it won't hold high rpm's. It drops down close to idle speed, then comes back briefly and dies off again. It never stalls, but it won't hold full throttle.
The plug looks good, the fuel lines are good, and when it runs, it runs like a top.
I'm sort of at a loss. It can't be a dirty carb, it runs perfectly at first. I took the fuel vent off, so it's not creating a vacuum in the fuel tank. The spark arrestor is also off right now, there's no back pressure problem.
The only thing I can think of is that the carb is leaking air in when it gets hot and then engine leans out? But I've tried adding some choke as it stalls, and that makes it worse, as does giving giving the primer bulb a squirt while it's dying. I've also sprayed ether onto the carb seals while it's running and there is no surging, so the seals seem to be good. I don't think I have a vacuum leak...
I pulled the cylinder off, the internals are clean and like new, no scoring, almost no wear, the rings look fine.
Maybe I'm losing spark? Maybe it is the plug? I would go get a plug today but they aren't available locally.
I'm stumped and the leaves are piling up. I'm stumped.
What have I missed?