600 HO Mystery...

[greasemonkey3406]

I have a friend that has an 06 switchback 600 with about 3000 miles. He just bought it from a guy for real cheap cause the engine is running like chit. It does not start when it is really cold, it backfires and runs really rough, when its idling it stays around 1650-1750rpm and sputters and backfires but when he puts it in reverse, it idles up to about 3500 rpm. Also, the max rpm that he can get is about 7500 then it drops down to about 6700. He had the engine apart to change the crank seals and inspected everything - even put new piston rings in and it has 120psi on both cylinders. He has correctly adjusted the tps. He said that the spark seems ok, firing on both cylinders correctly. The carbs have been taken apart and cleaned. He even installed his ecu on another sled and that sled ran perfectly. He also told me that he made a few resistance checks on the stator to check the wiring for it and it was all in spec according to the service manual. Anyone else had a similar problem like this? Or does anyone know of anything else that he can check. He is about the burn the thing.

Thanks.

 

[BB454]

600ho

Might try a different temp sending unit.

 

[Boston Racing]

Is it possible the flywheel key sheared. Maybe the timing is off

 

[MARV1]

Check the exhaust can, baffles are probably shot and clogging the outlets. Other than that probably the temp sensor. Clean out the airbox for crap.

 

[poliguy]

how is the reeds???

 

[Daggerboat]

Timing problem ?

With different RPM's in reverse I would look for possible timing issues...Since you tried the CDI already I would check the timing like Boston said

 

[cummins17]

is the crank twisted, real easy to check, find top dead center on both cylinders and mark them on the clutch and they should be 180 degres off from each other, ive seen a few 600s with twisted cranks, all it takes is the needle & seats to bo bad and fill up the motor with gas and you go pull it over and hydro lock and twist the crank

 

[faulk222]

greasemonkey3406 is this brads we found the crank out of phase last night

 

[greasemonkey3406]

Yes it is. Just tryin to get some info yor you fellers.
Thanks for all who posted with your suggestions.

 

[knee deep in it]

two questions on crank out of phase

1) what causes it?

2) what is the repair? new crank??

 

[cummins17]

two questions on crank out of phase

1) what causes it?

2) what is the repair? new crank??

All it takes is the needle & seats to bo bad and fill up the motor with gas and you go pull it over and hydro lock and twist the crank, or if the sled has been under water, # of things can do it but from what i have been seeing its the needle & seats.

repair is to send it to a crank guy and have him straighten it out, we charge 300-350 depnding on how bad it is.

 

[faulk222]

^^^^^^ X2 or in this case we know that the top end was done i would assume that it seized under load and bottem end was not checked

thanks greasemonkey3406 this was my next step