2006 450r not starting??

[yamaharider112]

I searched and i found some information but not really a positive answer. My buddies 2006 450r wont start. He has had it for about a year and put a esr air box eliminator on it when he first got it and it always fired right up. He put a slip on, on it for about 2 weeks then took it off. A week after he did that his bike is not wanting to start.It is jetted correctly, it does have spark, his filter is clean and his plug is good. He hasnt checked his valves yet but he is going to. I have read about a decompresser? messing up on this. Can someone explain to me what it is and what it does. It turns over fine and acts like its going to start but it dont. Sometimes it does but 98 percent of the time it wont start. We can pull start it and it starts right up and runs great. what do you guys think is the problem. His dealership didnt really help him any. Any ideas??

[QuadRacer041]

valves probably need adjustment. just needs to be done after so many ours of use.

[Flodies400ex]

well the jetting could be wrong and the valves do need a adjusting because that way to long with out getting the valves done but it should start but try not pushing on the gas when starting and turn up the idle then try and that and turn it back on but no for an fact that its the valves and you need to jet it again

[ghott]

My bet would be on the decompressor arm timing adjustment/clearance. Tell your friend to definitely check that. It is a known issue with hard starting 06/07 R's.

Also, the 06' R uses Titatnium valves, which wear out much much faster than the Stainless valves used in the 04/05 machines. If he hasn't kept them within the adjustment spec, it may be time for all new valves and seals.