03 800 RMK sputters when you hit throttle

[spm731]

Hi all, I am new to this site, but thought I would try it out. I upgraded to an 03 RMK this year because it seemed like a good deal at the time, but I have had some problems with it, so it hasn't seemed like a good deal since, haha. Anyway, after I purchased it, it turns out it was set up for altitude (I live in Saskatchewan, so we are as flat as it gets). Put in heavier primary weights, put a 540 main jet in (has a psi pipe), and just put the low altitude factory Polaris exhaust valve springs in. All these seem to have helped a lot and it is not as much of a dog anymore, but now when I hit the throttle hard the sled sputters a bit, or hesitates, and I have to let off and hit it a few times for it to reach rpms, but once it gets there it runs fine. Pulled the plugs and they are both brown. Running out of ideas, could this be a pilot jet issue? Any ideas would be appreciated.

 

[edge rmk700]

i have the same sled ,i have a slp pipe and air box mod,live in edmonton,sounds like the midrange is a problem,check the needle setting,should be on 3rd or 4th setting.i run 66 weights,neelde on 4 setting and main jet 400,runs awesome,let me know

 

[spm731]

I leaned the mains out a bit, and adjusted the needle. Set it at 4 and running 490 mains now. It was rich at 500, and now seems to be lean at 490. It runs great till about 7/8th throttle then you hit it again to max it out and it starts to sputter again. Pulled plugs and they are white, but it is too rich at 500 main. I was thinking that maybe it was the needle position is too lean and the main is too rich, but is it possible? I would have to set the needle at 5. I have also heard that psi pipes are crap and that a sled with these pipes will never run consistent, has anyone heard this as well?

 

[Polarblu]

When you are at wide open throttle your needle has very little to do with your mixture. At that point you are running on all circuits but your main is the controlling factor. This sounds to me like you are sucking air into the engine from a seal going out on the crank, and it has been over jettted to make up for the extra air.

 

[spm731]

After some more fooling around with jetting I realized that nothing was ever changing on the pto side, it was always rich. Tried to pull the exhaust valve out cause I thought it mighta had some gunk on it but couldn't. Ended up having to pull the head off to get a closer look. Turns out that side's guillotine must've gotten hot enough to melt but not fall off, was sagged and had an aluminum droplet formed on it. Plugged the holes in the block as best as I could and had to grind it off to get it out. Sled ran excellent for about 150 miles, but then I took out my crank, lol. Should've pulled it all apart while it was apart but did this all at 10pm the night before a sledding trip. I think some filings must've made their way down and took out a bearing, or maybe it was time, but I'm thinking it was self induced. Thanks for the help, now I get to build it up the way I want now I guess.