Here's the story:

For the past month or so, I have been having some problems with the Raptor. It started after riding for about 2 hours. Bike was running great then all the sudden it would bog down at about 1/2 throttle. I put it on the trailer until I got home. Put a new spark plug into it and all seemed fine. Rode about 2 more hours and the same thing happened again. Closer inspection revealed a bad spark plug boot. The screw that threads into the spark plug cable was broken off. I thought this was the problem. I replaced this and put a new plug in. Ran great for about 3 two hour rides. Today, it went again. Rode the trails for a few hours with my girlfriend and then started running the track at full throttle pretty much pegged shifting between 2nd, 3rd, and 4th. All the sudden it started sputtering. Since the fuel was around 1/2 tank, I thought maybe it was bouncing and sucking some air. I topped the tank off and rested about 15 minutes. Jumped back on and road at full throttle again. It ran great again for about 5-7 minutes and then it didn't want to run again. It idles fine so I limped it back to the trailer under about 1/10th throttle.

Additional info:

It is a 2001 purchased in February of 2001
Put a GYTR carbon fiber exhaust on, Dynojet kit, White Brothers PowerFilter, and opened the airbox up around June of 2001
Haven't rejetted or adjusted carb since June 2001 since it always runs great

It has been a little while since I adjusted the valves. Plan to check that tomorrow.
Replaced the choke cable with the upgraded one about a year ago. I am a little suspicious of whether this might be a problem with the choke. Will check this tomorrow.
Also suspicious that maybe the floats are screwed up. Not sure if this if a float problem would be in line with the problems I am having.

Any suggestions are appeciated. I will be stuck with the 400ex again tomorrow if I don't get this fixed.

/NotuRaptor

 

sounds to me like one of the carbs is off of its boot have you checked them?

 

yamaha4life

I will look closer tomorrow at the carb boots. I did a real quick glance and they seemed to be on. I thought carb boot problems caused consistently bad performance problems.

/NotuRaptor

 

fuel injector cleaner

 

A dirty filter or a loose battery cable will cause problems.

 

When I purchased my 01 Raptor both carbs were off the boots and it ran pretty good. Then I fixed everything and boy did it run better.

Blueleader is right, it could be an electrical problem.

 

I'm not sure if there is a filter/screen on the pitcock, if there is it sounds like it could be dirty.

 

1-If the intake boots are torn, then you will not notice until you slide the carbs back and lightly tug on each boot.
2-Is the crossover breather tube partially blocked (one line running from the top of the carbs)?
3-make sure the "pop-in" needle clip retainers are still in tact and not popped out.
4-is your choke sticking wide open? THis can be viewed by opening the top of the left carb (as you are sitting on the bike)....it's a hole that opens up when the choke is operated and is located in front of the needle assembly.
Lastly, and my first thoughts on your problem, were too clean the carbs really good. Get about 2-3 cans of some cheap brake cleaner and clean everything twice.

 

If you are around sea level, I would recommend 148-150 mains along with 1 setting leaner on the needles than what dynojet recommends (I think they recommended the 3rd slot from top and 4th cleared mine up perfect). Dyno-jet done all their testing with the lid on. The lid off creates mid range turbulence, so the needle change setting fixes this. Just try it.....the machine will respond better.

 

Going from the 3rd groove from the top too the 4th on the needle would be richer.