Is it my jetting or something else? I need Help

[ZSK]

My friend just bought a 97 300ex, for $1500. As far as we know it has no motor work, and still on the original air filter. He has a 39 tooth rear sprocket, which should give him a little more bottom end from what I've read. Running wide open down a gravel road he will pull away from me, pretty steadily. I'd say at least 3mph faster. He also beats me pretty bad in a drag race, and I'm the better rider. My engine is bone stock except for a K&N air filter and his is stock as far as we know. What's going on here? Thanks for the help.

[sprtrx300ex]

Check your tire sizes. 20" give you better acceleration and 22" give you better top speed. Rider weight might also be a factor. Thats all I can think of.

[cals400ex]

i am not sure the sprocket sizes on a 300ex but when going with more teeth up front and going less teeth in the rear will both give more top end. going with a smaller front or a bigger rear will give more bottom end. also, have your valves been adjusted lately? my valves needed adjusted bad and it ran like crap and i did not know why. once i adjusted them, the bike ran good. also, with a K&N air filter, you may want to go up one size on the mainjet. i have also noticed that when a motor is about ready to need rebuilt, it runs faster. i know that sounds kind of weird though. i don't know if the cylinder wall somewhat expands and there is less friction or what.

[remlapr]

If you have two pretty much stock bikes and one is consistanly faster dragging then the other and you can eliminate tire size, gearing and rider weight, etc. - it is probably compression - his bike may have low hours on it compared to yours or may have been broke in better. I have seen a pipe only without re-jetting 400ex beat one with pipe\rejet\choke removed\welds ground\hot cam 1\sparks key. And the riders were close to the same size and the modded bike was running lower gearing.

[ZSK]

His is a '97 and it has deffinately been run ALOT more. As for the rider weight, tire size, rider ability, etc... He is 20lbs heavier than me, we both are running stock (22") meat, He just started with a clutch and just started riding a year ago, I've been riding since I was 7, I can waste him on the trails but it's the straight line that he kills me. I'm thinking that is it my jetting, because I bought a new plug, when I fouled out my old one, and checked the color after 3-4 hours, half of it was a perfect tan and the other half was jet black, does this sound wierd? I pulled the airbox lid and rode it for about 20 mins. noticed some more power right away, went back in the garage checked the plug and it was ghost white, so I put my lid back on. Thanks for the help anyone else have an opinion?

EDIT: also I adjusted my clutch last night so we'll see what happens when we ride today.

[cals400ex]

i am assuming you already adjusted your throttle cable??? that makes a pretty big difference.

[Scott-300ex]

check your tire pressure too, also, i heard no two bikes are alike so maybe it depends on who put em together or like said up there how they were broken in

[ZSK]

I found out my problem. I pulled my plug and it was jet black, so I opened up the airbox a little, I unclipped the back closed the clips so the lid was resting on it. Got better. So I pulled the lid off. and now it's white with a hint of brown. I went to start it today and it blew the carb boot off the engine (in front of the carb) so I stripped it down and reattached the boot and tightened the clamp, now it's perfect maybe a little rich yet but I gained a lot of power!! 4th gear wheelies now with a tug
OH YEAH!!