There was a post many months ago about a 650 owner that had a problem with his fuel tank vent. He was experiencing no start and it was traced to the vent breather. The dealer recommend he take it off. Once he disconnected the breather he had no problems. Another concern could be how full are the fuel tanks and the contraction and expansion due to temperature fluctauations of the gas. This could cause the expanding gas to over flow into the vent line causing a blockage (air lock). The only fuel related problem I've had, is malfunctoning sending unit due to I over filled the tank. Just my thoughts hope it helps.

 

How would the buildi up of gas in a tank vent prohibit the machine from starting? If this was the case, why was the crank seized up so tight that it couldn't be turned over? Just wondering...