2004 300ex Hop up

[Andrews]

Hi All
I live in South Africa, and I bought a 2004 300ex in October last year. I have installed a K&N filter, Dynojet Kit and a Yoshimura slipon cannister.
I have also changed my sprockets from the standard front/rear 14/38 to a 15/36 ratio for some more speed.
We put it on a dyno this week, and found that the jetting is wrong- 142 main from the Dynojet Kit.
However it does rev to 9,800 in 3rd gear before it starts spluttering and loses power.
Output measured on the Dyno was 18HP and 21NM Torque.

I can't afford a 450 at the moment, but I really want to do the Roof of Africa this year on the 300ex.
Problem is I don't want to get drilled by people on Blasters and LTZ250's
What can I do to make this thing go properly?
What can I expect from a 300ex?
I am prepared to spend the money on it if the performance benefits are worth it.
Any advice would be appreciated.

[sprtrx300ex]

A 142 sounds a little high. Id try something lower like 130, then run a plug test.

300ex's are great for woods riding, but lack a high top speed and jumping abilities.

[m250r]

Dude, are u kidding me?:huh z-250s and blasters smoking you? Theres no way. anyway..i would either bore you engine or get a piston.

[phebus]

If you had it on a dyno, and found out the jetting was wrong, why didn't you re-jet and dial it in?

[300EXrider02]

sorry but a 15/36 sprocket set up is a tad too much, I think you would be good with just 14/36 if that with 18" tires, because stock is 13/38, its a bit much for a 300ex engine to be trying to dish out that power to run that gearing

[cals400ex]

if your running the stock size tires, i would either take off the aftermarket front or rear sprocket. both will be overkill and probally harming more than helping. also, go down on the mainjet. that should help your power out. another thing to check is your throttle cable adjustment. make sure there isn't 1/4 inch or more slack in the lever. if so, tighten it down until there isn't. this can really hurt performance.

[Andrews]

Thanks to all for the advice.
We sent the head off for polishing and porting, and are going to redo the cam for a better toque curve. Then we'll get the jetting right on the dyno. Will try the 130/134 first. I did have a 125 in but it ran too lean.
Can you believe this country, - I have to wait 6 weeks for a Yoshi header pipe. By the way, my mistake- the sprockets are 14/36. I think it will go OK with this ratio, but will find out once the motor runs properly.
Will check the slack on the cable too.

[300EXrider02]

what size tires are you using on the machine? i run the same sprocket set-up but with 18" mx kenda klaws, it would be best to run this set up with a pipe like you are doing, but a word of advice is that if you are running 22" or 20" i would do down on the gearing, go to a 37 if 20" or to regular 38 if you are running 22", my 2 cents, good luck with parts;)