I had some troubles with my scrambler 400 this weekend. What happened is everytime my scramber needed so low end power nothing was there. for example from a stopped position if my front wheels were up against a small log I would not have the power to get over it, I was stuck in a mud pit and my wheels would not spin like they usually do, or climbing a hill would be so slow I was worried I would not make it up. In all of these situations I was at full throttle from a stopped position, but my RPM's would not climb. When i am on the gravel road there is not problem the machine seems to run good, it goes quick and starts off the line just fine, it is just when I am under load. I am suspecting either 2 things the weekend before I got my belt pretty wet and am wondering if I may have smoked the belt? but wouldn't the rpm's still climb on my machine while creating a burning rubber smell. The only other guess I have is before I went out I re-oiled my K & N filter without washing it, I am wondering if maybe not enough air flow flow is getting through. Any suggestions would help, has anyone else experienced this problem.

 

One thing I would check is if it had gotten wet maybe some debri is caught in the secondary not letting it shift back all the way out. Or at least something that gives you that effect. With it not shifting all the way back out it is, in effect, like starting out in second or third gear on a shifter quad.

 

I would start by removing the clutch cover and doing a little cleanup. You need to remove the belt, blow out everything, then lightly sand the clutch sheave faces with some 400 grit paper (I like to do the primary with the engine running, but dont really recommend it). Use some non-residual cleaner such as brake cleaner to clean all parts, then put it back together. The belt should have slick sides where it slips on the clutch sheaves. If it has a roughened texture or cords fraying off, then put another one on it. If the bike takes off on a gravel road then the air filter should be all right. Bubba

 

having the same exact problem right now!! this weekend i was hittin some sweet sand trails but i came around a corner going about 43 according to the trailtech and just went straight into about a 7 inch deep puddle. the engine bogged and died. it took a few minutes to start but wen i did it would just bog even on flat trails unless i gave it full throttle to start it then if u were going 30 and let off teh gass for a second and then went back on the gas it would bog then start to speed up wen it hit its powerband. not sure whats wrong but it didnt do it after i went swimming and came back to ride back to the house because the engine cooled and i took the prefilter off and cleaned it. i played with the air/fuel mix screw but it seemed to bog less when i turned it out. i will be getting my 30 pilot jet soon so i will see if that helps

 

thanks for the suggestions, I will pull the clutch cover off tommorow and do a bit of maintenance, thanx for the suggestions, I'll post and let you know how it goes.

 

if the clutch cleanup doesnt help, clean the air filter

 

i would change the spark plug sounds like an old plug to me.....

 

Yeah the plug is exactly what I thought, So half way through the trail ride I changed it, the old plug was shot, and the new one I put in did wake it up a bit but the difference was not enough to improve the performance.

 

if temps were warmer/more humid than normal,.. i had the same prob on my sp 400... it would "load up" and bog... couldn't feather the throttle enuff to get the rpms up,.. just dropped the position on the needle 2 spots and it cleaned right up.
The belt/clutch stuff makes zero sense to me,... it would still rev like hell.... just not go far,.. it's ignition or fuel that causes a sustained bog.

 

re-oiled a filter without,washing,clean,then dry it up,is a very bad thing to do on a 2 stroke,,,we just had an explorer 400 doing the same thing some years ago cauze of a non-cleaned air filter,carburator become real "finicky" when air filter is dirty.