my uncle isnt what u call a machanic at all and his sport 400 is running like crap ( i think jetting) he gots a rcr pipe and a clutch kit he got a guy to put it in for him and do the jetting well i dont think the guy new what he was doing b/c now after you are almost at half throotle- full throotle it feels like its going to bog out a lil bit....well the question is if it is the jetting can u tell me what size jet he should be running and also where the clips and all of the other stuff should be sat at....b/c he bringing it up for me to fix it and take her for a few rides and i really want to get it fixed to see how it rides b/c im thinking about getting it off of him

 

I had the same prob when tuning my carb. First start it up and run it full throttle for about 100 feet, shut it off and then stop. Pull the plug, odds are it is going to be black or a dark brown. If that is the case then drop the main jet down one at a time until that spark plug is a light brown. Personally I like to keep mine on the dark side, that way it wont run lean and burn up the motor. I would rather put in a new plug then replace pistons or worse...

 

Just so you know I am running a 260 main jet.

 

whatis your elevation? at sea level it should run a 260 and the needle in the middle.and this is still a little rich
also check to see if the secondary spring is set right

 

using the plug is good but to have a really good idea of whats goin on dont jsut look at your plug. drop main jet sizes one at a time until the bog goes away. that is the safest way to do it. same with teh needle jet. good luck. scott

 

I'm running a 260 main also with the same mods. Runs great.