I have a Honda CRF450, and the bike suddenly quit starting. IT feels like the kickstarter pushes way too easy, and the only way I can get the CRF450 running again is to get towed behind a car for a few hundred meters.
By: ThaiDesign (offline) Saturday, 17 April 2010 @ 11:49 AM ICT
The Honda CRF450 is a great motorcycle, and requires the usual maintenance to keep it running. I'm fairly certain that if you remove the Keihin FCR carburetor, you'll notice that the throat if the carburetor is black. This is a telltale sign that one, or both, of the intake valves is not sealing properly and combustion is actually leaking past the intake valves and back into the carburetor and intake tract.
I'm almost certain that if you checked the valve clearances, you would find the exhaust was tight but had a gap, and that the intakes were jammed tight. When the valve stems stretch over 0.1524mm, you lose compression, and starting becomes a nightmare. Rebuild it, and you good to go...