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Update
FINALLY the weather is decent enough here to get the 125 Coolster pitbike back together today (I don't have a garage). Here's what I did and here's what happened:
1. Ultrasonically cleaned the carb and rebuilt her. I left the 98 main jet in.
2. I rebuilt the entire fuel system (i.e., new lines, new inline fuel filter) and cleaned the tank thoroughly. The dang line out from the tank had a pine needle in it! No wonder the thing was behaving like it was starving for fuel at times! The tank was filthy and had various junk in it. The kid that owned it before apparently, at some point, left the gas cap off or something and some trash got in that tank. The old fuel filter was filthy. I'm amazed the thing ran at all.
3. I got her all back together, got her fired up, adjusted the air/fuel mixture screw, the idle screw, and she starts right up now.
HOWEVER, she still seems to want to bog down a little when you get to 3/4 to full throttle. When I ran her up the street tonight, again after running her full throttle, she ran well, but she didn't run long. She started bogging down and just wanted to cut off and then finally did, even when I let up on the throttle.
It is indeed as if the valves swelled (or something expanded) and the internal engine dynamics changed. That's quite weird considering right before I wintered her I adjusted the valves to spec. I even double-checked them to make sure I did it correctly.
She'll run ok for the 11 year old, but if you really want to open her up, she's just gonna act funny until I can get this figured out.
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