I went to a local bike meet Saturday. They had a dyno competion. I new there was no way my stock F3 could win anything, but I figured it was free. The printout would give me horse power and air/fuel so I would at least know if the carbs need adjusting. Other then the rectifier frying I've had no trouble with the bike since I started riding it 4 months ago.
The tech hopped on it and drove it onto the dyno with no trouble. He shut her off while he strapped her down and hooked up the O2 sensor. It wouldn't start back up. I got up there and choked it and it started. I let it run for a minute then shut off the chock. The bike idled fine. I got down the tech trade to start the run but as soon as he touched the trottle it would stall.
He tried 5 times and gave up. He wheeled the bike off the dyno and gave it back to me. I started it back up and it ran fine. No issues at all. What the hell could have caused all that?

 

Can you describe what you mean by "wouldn't start?"

 

Cranked over, but wouldn't fire. Chocked it and it finally fired and ran, shut off the chock and it continued to idle until you tried to throttle.

I'm wondering if it had something to do with him stuffing the o2 sensor 3 ft up the tail pipe, but I can't imagine what that would have interfered with.

 

Well, exhaust. If the engine can't get rid of "air," then it can't take any in, and it won't start. Sounds like he somehow partially blocked off the exhaust, which is why only opening the choke to allow maximum airflow IN would make it even begin to start.

Assuming the guy was using the same sensor he used on all the other bikes, and its not that big, and he know's what he's doing, that leads us to believe you have an airflow obstruction somewhere to begin with, and that little added pressure in the exhaust pushed it over the edge into not-running-land.

Bizzarre, I admit, but that's all I got. Check your airflow paths. Mice LOVE to build nests in exhaust pipes.