I have a 2002 400ex with hmf comp pipe, K&n air filter (with air box lid on) havent had time to adjust carb 100% right, i got it somewhat close, im thinkin i might take the lid off and play with some jets and the needle to see if i could gain some more power...not sure about that..if its worth it or worth the risk i do alot of trail riding/hillclimbs/ mudding and where im at can be very dusty at times. i just put some itp ss112 rims with holeshot gncc tires on it.20-10-9 rear and 22-7-20 front. i went riding last weekend and noticed a huge difrence, that i lost alot of bottom end, i mean it was bad, i about got hurt bad a couple of times. i hit some of the usual hill climbs and noticed when i do them in second in bogs down or has no power/torque what so ever. I had to stay at the top end of my gears and scared the sht out of me cuz i hit a big root and the front end came up a little to much so i had to let off....then when i i went to get back on the trottle i had to rev it up real high. oh and i cant or have trouble taking off in second...b4 i got the tires i could do it no problem and the bike would take off like a rocket....ok now to my main point should i get a 14tooth front sprocket or what? im confused about what to do for the sprocket. maybe get a 14front 39 back?i am also putting in a stage 1 cam. i want this bike to have alot or torque im not so worried about top speed cuz i mainly do trail riding and almost never hit 4th, maybe here and there i can find a trail for that. also just throw some more tips about what i could do to make this the "perfect trail bike"... one thing is if i do make it a torqey as hell what would be best to do, to help me keep the front end on the ground? i know i could extend axle or hubs, but that is a compromise for going threw trees. i could lower it but yet another compromise for hitting/scraping rocks. what should i do?

 

I'd just go back to a stock chain and sprocket setup if you mainly do trail riding. 15/38, mine is stock and it has plenty of grunt and torque to handle all trails I ride.

 

I want to keep my tires and rims on it...i like the clearance and the handling of these tires. and my chain and sprockets are stock right now...its boggs down so much/doesnt have really any bottom end.im just wantin some opinions about gearing like if i should have a 14/38, 14/39, or maybe 13 front sprocket (not sure bout that tho....sounds like it might be too much)..if i do get a 14/39 how are 1st and second gear? and when or if i get it to have ALOT of torque what to do to help front tires stay on the ground?

 

Sounds like you need to get your carb tuned first. Proper jetiing will make a world of difference.

 

i ran a 13t when my motor had stock internals.. i lost my top end and would hit the limiter quite easily in 5th but i could almost crawl the bike without stalling. I would go with a 14t for your setup

 

I am running basically the same as you 02 400ex with hmf slip on exhaust & k&n filter. I was in desperate need to change my chain due to a bummed skid plate digging into it. I will let you know my results after I install. And I did feel that the stock setup had an adequate amount of torque but I wanted a little more. I will let you know the exactly what I am installing and I'll let you know how I feel about it after installed.

 

Yea forgot to mention Jetting, If you live in the same region as me your going to need to change the getting with the seasons. I just went to ak farms and my quad would run good for a lil bit then bogg down. Whether it was the jetting and weather ( rode in the cooler months without a problem) but yea I need to adjust my jetting as well. I can say the jetting does make a significant difference prior to the sprockets.