First build stopped working while at full throttle

Just got my bike running today (In between master links breaking, but I think I've sorted that out.). It ran fine earlier (with full throttle) but after shortening the chain a link I took it out for test ride, drove it a quarter mile then brought it to full throttle. After holding it for a moment the engine noise changed (pitch became higher, maybe a higher rev too) and it stopped driving the chain. Tried starting it again, but it just makes the same noise, adds no power to the chain, and soon dies out because I had forgotten to mess with the carb screw to get it to idle properly earlier today when it was working.

This is a BGF kit I ordered just recently, don't really know anything about engines so I figure I can learn something. I was advised to keep the throttle down during the break in period, which I ignored because I'm not going to let some chump instruction manual push me around. I guess I had it coming to me. So is that the reason it broke, or is this something else? I've taken off the plate opposite the clutch on the engine and those two gears seem fine, I can spin them with a screwdriver and see the chain move and hear the piston so everything still seems hooked together. The next step I'm seeing is to disassemble some other part of the engine and poke around. But I've got no idea what that entails, so if anyone's got some advice or could tell me what I've broke I'd be greatly appreciative.

Unrelated note, my leg now carriers a stylish pink reminder of how hot mufflers get.

Fixed it. I didn't notice that my spark plug had unscrewed itself and was sitting on top of it's hole, did not know that was possible. Guess this is a combination of vibration and whatever explosions were going on beneath it. I have to install the spark plug by hand (small frame, no tools can fit), which apparently isn't enough. Still can't tighten in past where my hands can do it, I'll just have to keep an eye on it.

GearNut said:

One other thought, slant head cylinder heads can be flipped around to point the spark plug in the opposite direction. If you did that, would a regular spark plug socket fit?

Click to expand...

Thanks, that worked. Flipped the head and can now fit the tool in. Thought it was odd that my slant head came pointing straight up like that, but didn't know you could just change it.