You need a special compression tool to measure on the 660. The sparkplug is down in a long hole. I hate it when they do that.

 

yeah.. its a DOHC compression tester.. i have one at home so ill be in luck for that one.. Do you know how many ft lbs its supposed to have?

 

Compression is good.. any other ideas??

 

Come on guys.. How about timing?

 

You could check the timing, but normally if the timing was that far off you would have more problems. I have had bikes where the timing was off and they didn't do anything like this. Normally if the timing is that far off it won't run at all. I'm thinking out loud here, but if you have fuel coming out of both carbs, that means it's coming out of at least 2 valves because one carb feeds 2 valves and the other carb feeds 1 valve. If you have 2 valves open during the combustion process, then there's no way it would ever start.

So, if the fuel mixture is not being sucked into the engine as the piston is going down and the intake valves are open, maybe you have pressure coming from somewhere else that is blowing the fuel back out. I don't know if it's possible, but maybe there is a seal in the engine somewhere that is letting crankcase pressure or oil pump pressure be bled off in the combustion chamber. Or maybe the head gasket is blown? I'm just trying to think of all wierd possibilities. When did all of this start? Was any work done on it before it started happening?

 

DAN DOES THE BIKE RUN WITH THE AIRBOX IN PLACE? MY CONCERN IS IF YOU CAN SEE THE FUEL SPIT BACKWARDS YOU PROBLY DONT HAVE THE FILTER ON/ WITH IT OFF YOUR GOING TO RUN VERY LEAN. ALSO WITHOUT THE FILTER AND COVER NOT IN PLACE YOUR NOT GETTING THE VACUME NESSESARY TO PULL THE FUEL /AIR MIX THRU THE CARBS.

 

Yeah these are all possibilities i suppose but idk where any excess pressure would come from except the compression stroke.. But i bought the raptor from my buddy so i know its whole history. the six bolts in the flywheel got sheered off(the ones that connect the flywheel to the big starter gear on the crank).. we replaced them.. it happened again.. we thought we got to cheap of bolts for the high compression.. we ordered new from Yamaha.. it happened again.. we got pissed.. we welded the flywheel to the gear.. it ran fine for about two weeks.. then this problem came on suddenly.. it has no aftermarket accesories it is completely stock

 

The bike runs the same with the air box in place and the filter inside and with all hoses and everything hooked up.. it still runs lean..