check the float level. mine was over 1/4 inch off from the factory and it will cause major headaches when trying to modify the jetting from stock.

 

thanks for the replies. I was just looking at my dynojet paper, and it shows that the fuel screw/pilot+neelel overlap at 1/4 throttle. I may be rich on the pilots. I have them out 3.25, so I'll turn them in 1/2 turn and see. If that doesn't work, I'll try to take out the s/a or fabricate something to cover the 3 holes in the exhaust.

I would try the 142/144mj, but man, is it ever a pain just to get to them. I could change a main jet on my 400ex in less than 2 minutes. only the drain plug needed to be removed to access the mj. But hey, this thing is way more trailable. Smooth torquy power, yet explosive if you want it to be. and reverse, and the susprnsion is more plush. no regrets buying this thing so far. and the problem I'm (and other people) are having is our own fault. If you tinker or mess with the stock setup, there is always the risk of messing something up. But it's fun, and most importantly, more power.

I'll keep on trying and let you guys know how how it goes.

 

Just got an idea. The needels start to open at about 1/4 throttle. They lift and fuel flows into the mains. so maybe the mains are flowing too much fuel through at 1/4 throttle. I try the 142/144 when I get some time. It really sucks because there are so many bolts, and screws to take out, and if it doesn't work, all that wokk and wearing of the threads for nothing. but It will be my last resort.

 

It will work, I went the same route. I even tried richer and man was that a mistake it wouldn't even take any throttle. I probably could do it in the dark now , but it was worth it , runs great. Whatever DJ recommended , I am pretty sure I went two sizes down to fix it. Doesn't matter if it makes sense or not if it runs good and the plug is good it's right.Good luck.

 

The bottom line is you can & probably will try every jetting combo possible. You'll even check non related jetting issues such as, air leaks in exhaust, valve adjustments, spark plug gap/wire/plug itself, etc etc....It just doesn't matter, too much air into the filter creates some type of turbulence that creates a 1/4-1/2 throttle problem.
Now, how did I deal with it, I discovered that the problem is most noticeable when in neutral & your revving the atv. To accomadate, you wind up jetting on the rich side(clips=4th or 5th poss) & you think you have the problem resolved, almost! Then you take her out for a test run(you must change gears here) & on your first major acceleration & or hill climb, she really bogs & sputters around 1/4-1/2 throttle. So you do some trail side jetting & move the clips up a notch or two(depending on temp/elevation) & she runs like a champ @ 1/4-1/2 throttle & pulls your arms off from 1/2-full throttle, life is good, enjoy it! You'll find that it doesn't get any better unless you buy diff types of carbs(=$$$). Even with the optimum jetting you will still have the sputtering from 1/4-1/2 throttle when in neutral & revving the throttle but you won't notice it when riding, that's all that matters & that's the best it gets!
My advice, if you want max hp, remove the lid, use a prodesign or equiv type of filter, buy a slip on or full exhaust, bump up your Mikuni mains to around the 160-170 range(leave the DJ kit at home for a science project & save some $$ too), run with the clips on 3rd or 4th position & fuel screws around 3 turns out. Use richer mains/clip pos in the winter & leaner in the summer, enjoy!

 

Chimmer is right on the money. I have been through it, Chimmer has obviously been through it and so have many others. Get it close like Chimmer said and leave it alone. Unless you go the expensive route like me and buy the FCR's. The only reason I did is because I had a new motor built.

Also, you should check your float level too. ALOT of Rap owners (inluding me) have found the floats to be WAY OFF. This will help too!