Well the yamaha guy most likely wrong as all the microfiche I look at shows a needle jet. Following link shows the jet up close and how it should be viewable popping up when looking into the mouth of the carb...No such thing there when I took carb off.

http://myural.com/keihin_32cvk_disassembly.htm

http://www.rosevillecyclecente...ki&year=2003&fveh=1829

 

I have an 02 and had the same problems. So for what its worth now here is what I found. The vent hose they used for the carb is a piece of crap, ( The 1 that goes from the carb to under the seat ) When mine would act up I found that blowing through the hose would help it for awhile, UNTIL I found that they routed the hose too close to the exhaust and it had a soft spot in it from the heat and would kink at times.

I replaced the hose with 3/8 fuel hose, ( alittle tough to work with ) but that solved ALL my stalling and hesitateing problems.

 

hey mine does the same thing but it is off and on! i havent cleand out he carb since new? did the claning work for you? do you knwo what the stock compression should be at on an 02 400 2wd?

 

If it helps anyone, i had problems withe the vacume fuel valve also so i put a regular inline on off valve after the vacume valve and i just leave the stock valve on prime all the time. Turn the inline valve off whenever i turn the atv off to keep it from flooding anything. Seems to work great.