I've got an engine stutter when I'm under load, say going up a hill in hi range and I squeeze the throttle to the handle bar it starts to loose power like it's overfueling. I heard that there was some change up to the carb (rejetting) but can' seem to find anything out. Any information would be helpful

Thanks

 

It's runnig too rich. You need to drop the main jet down and lean it out. It was an issue from the factory.

 

there a few post about this not too long ago if you do a search on the loosing power on the sp. 400.