Today my brother and I took out the 4 wheelers. His SP 600 started and idled fine, but did not run very well past about 1/3 throttle and/or about mid RPMs. The more load it was under, the more it sputtered. The machine has always run perfect before this and it only has 85 miles on it. If you put it in neutral and rev it up, you can almost get to peak RPM, but it still sputters just a tiny bit. We were guessing he could have had bad gasoline, but I would think it would act funny at all RPMs. I was also wondering if the rev limiter was a factor, but since it would rev almost all the way up (in neutral), I think it rules that out. Any ideas? One other thing, on the way up to the mountains it did get a lot of spray off the road that formed ice on the front, but don't know what that would have affected.

 

Check your TPS. Tighten throttle cable.

 

TPS - is that the throttle position sensor? Is that the same thing as the ETC? Does it matter where I tighten the cable at - is there only one adjust?

 

You should check for water in the system. If the machine has set for awhile, the water will sink to the bottom of your tank. When my Dad's had this problem, we took off the fuel hose at the bottom and drained some in a glass, it was full of water. We ended up draining the entire system. Check your spark plug too.

Scott

 

There's a spot to tighten the cable just before the handlebar. Just pull back
the housing a bit to make the adjustment. I'd still check the gas for water &
plugs like Scott says.

 

Tightened up the slack in the throtte cable and that did not fix it. Checked the sparkplugs and they were very sooty and black. Looks like it has been running rich. I will buy 2 new NGKs for it. Drained the gas and I could not tell if there was any water in there or not. My gas can is opaque and I just cannot see if there is any water in there. My guess is probably not. I will try fresh gas and see if that fixes it. Is there any way the rev limiter could be kicking in and causing this?

 

Might want to check the choke linkage for proper opening and closing. I've seen that happen on sleds before, the choke stays slightly open and floods out the engine when its wormed up. That would also give you a black plug.

 

I have checked the choke already, but I will double check again. It looked to be adjusted properly and operating without getting stuck. Thanks for the suggestion. Hopefully tomorrow I can fill the tank will fresh gas and test that theory. If that does not fix it, I am thinking rev limiter slowly going bad. It is still under warranty and I can then turn it in to the dealer, but they are so swamped I hate for them to dink around with it for ever and keep us from riding. Anybody have any other things I can check ?

 

One last thing to mention is the problem does not occur until the RPM's reach a certain level (about 50% RPMs). The more load the engine is under, the more obvious the sputtering is. It really acts as if the mid to high speed circuit is too rich. But I know this cannot be the case since the jetting has not changed and the area and temps in which I ride have not changed.

 

Just an update for anyone interested. Have put another 60 miles or so on the 600 and today, for whatever reason, it fixed itself. No more problem whatsoever. The only thing I can think might have happened was due to vibration. We were running over some huge fallen trees and it was shaking the machine really well, so maybe that had something to do with it. Anyway, the thing fixed itself and I guess I will keep driving it and see what happens now.