This can't be right, What am I missing?

[QuicktimeRacing]

I have a 99 400EX which has an HMF muffler, 14 tooth sprocket, Aluminum airbox with K&N air cleaner, and 21x11x10 Sand Gecko paddle tires. I took the bike to Buttercup a few weeks ago and noticed that it was absoluetly pathetic when racing up Comp hill. Basically whatever gear I went through the whoops in is what I would be lucky to be in at the top of the hill. Most of the time I could keep it in third all the way up the hill but sometimes I would have to downshift in to second. I tried starting out in second through the whoops and even went through them in third gear pinned but it just seems as if my bike lacks the power to get the wheel speed up. What am I missing here? I am not sure what the jetting is set at but was told that it was already set and I shouldn't have to mess with it. On flats the bike has tons of bottom end and keeping the front end on the ground is a chore in itself. Is this just a four stroke thing that I should get used to or is there an obvious problem here? Let me know what you guys think I should do to better the performance... Thanks, Trent
http://g.myspace.com/00052/32/50/52510523_m.jpg

[Rico]

Might be running rich on the main jet and is just a slug on the top end????


May I recommend a big bore kit.....:devil:

[QuicktimeRacing]

What size jets should I have in there? Does the jetting for altitude affect four strokes as it does the two strokes?

[crazyatvn]

I would say tall tire. Sand takes lots of power and taller tires with good bite might be the problem. But I am not a sand expert.

[muddy400EX]

dont know much about sand either but it does take alot of power. id get smaller tires tho cuz your gonna need the torque!

[NX400EX]

I agree with muddy400ex the small tire about a 18 or 20 is your best bet. You might need to get a 16 tooth sprocket for the front or a smaller on the back. On the jets i would check them and check the specs for the altitude. As far as the big bore kit goes i wouldn't, i did with my first engine and it didn't last. My new engine has lasted twice as long and has a little bit better power. Mostly on the EX its the gears the motor is one of the hardest running motors there is. Hope this helps.

[asdf450r]

drop the front sprocket down a tooth to a 13.. doesnt seem like a jetting problem, it seems like a torque problem!!!

[QuicktimeRacing]

Alright, I think that since everyone keeps telling me the tire size is hurting me I'm going to change my sprockets to compensate. I realize the Geckos are heavy so I will change them when money permits. For now, I think a sprocket changeout should get me better off. I'll let you guys know any mods I make and let you know how they work. Thanks for the help guys, Trent

http://g.myspace.com/00052/32/50/52510523_m.jpg

[js3350z]

Originally posted by NX400EX
I agree with muddy400ex the small tire about a 18 or 20 is your best bet. You might need to get a 16 tooth sprocket for the front or a smaller on the back. On the jets i would check them and check the specs for the altitude. As far as the big bore kit goes i wouldn't, i did with my first engine and it didn't last. My new engine has lasted twice as long and has a little bit better power. Mostly on the EX its the gears the motor is one of the hardest running motors there is. Hope this helps.

you are backwards with the gearing, for more torque you would go down in the front or up in the back (you said larger front, and smaller back which would be more top end)

[jeepcj5nut]

QuicktimeRacing:

I live in Az and Ride in Glamis as much as possible. We went to Gordons/Buttercup on Thanksgiving and I couldn't even make it to the top of "comp" on my 99 400ex after hitting the bottom pinned in 3rd gear. I run a unifilter/DG exhaust/14front 36rear sprockets/and 20-11-9 Sand Stars.
I also noticed that the bike was running hotter than normal!!
I rejetted from the stock 148 main to a 152 and it helped some.

I got an outerwears cover for my airbox and ripped the lid off. Rejetted to a 160 main and left everything else the same.
Went to "G" 2 weeks later and didn't have any problems making the hills!!! The bike did great and was running a lot cooler!!!

Rejetting only takes about 3 minutes to do "don't even have to remove the carb" and will give you back some of your power!!!

I think if you go all the way down to a 13 tooth front you are going to be bouncing the motor off the rev limiter too much.


Good luck,
Shawn