Help with 300ex jetting

I have 2001 300ex with K&N air filter and I'm probaly getting a new exhaust soon, like a fmf megamax II or a WB e-series. I just need help on jetting. I don't want to hurt the life of the engine and don't want to cut holes in my airbox lid. Any info on jetting would be great, especially from anyone who owns a 300ex and has gone through the process. Also I don't want to go to the local dealer and get ripped off.

thank

[sportraxrider10]

i have a fmf power core 4 on my 300 and i have a 130 main jet and my dad turned the screw someway, i dunno. it runs good so thats all that matters i also have a k&n air filter and jetting

[danney f]

You can go to their web sites and they give you a good idea on were to start at after adding a pipe. FMF's page gives you the jet size for the carb with a KnN fillter and a stock lid and without the lid. I would try there first. I'm not sure about the other muffler web pages but I'm sure they will too. I run a #134 main, but your bike is probaly set up differant. Hope this helps out some.

[mxracer08]

I have a 160 main jet with the needle in the middle. That is about the best combo i have found for mine, but of course, it would be different for a stock bike. You really have to just do some trial and error. Try different sizes and ride it for a while and then check the spark plug ( when it cools down). It should be a light brown to dark gray color on the tip of the electrode.

[300exryder]

You're running a 160????

I have a FMF MegamaxII with K+N Filter and Precharger and i went up to a 128 MJ from the stock 122. I left the pilot stock and dropped (maybe raised -- dont remember) the clip one notch. The air/fuel screw was turned out about 2 and 3/4 turns. If im running lean, lemme know. It is running fine and rarely if ever backfires on deceleration. I didnt do the plug test. I have no other mods other than what i said above as far as motor work goes except for a new clutch.

OT: Does anyone here have a 14 tooth front sprocket for a 300ex?? How easy is the installation -- any new parts/tools needed?? Some friends said that if you change one sprocket/or the chain, you should also replace the other sprocket/the chain. Is this true? I found a cheap (6.99) front sprocket in the Rockymountain atv catalog -- i think it is made by primary drive.

[mxracer08]

it didn't make sense to me at first either, but that's where it runs best for my bike.

[mxracer08]

i have a 14 tooth front sprocket and I had to cut the stock chain off to do it. All you have to do is take off the plastic guard in front of the sprocket(10mm bolts) and then there are two bolts on the sprocket(also 10mm) and then turn the little piece in front of the sprocket, while puling out a little bit until it comes off. Then the sprocket comes right off, no problem.

[300exryder]

Thanx for the help -- im soooo sorry about the 160 MJ thing -- i totally missed the 330 kit that is in your signature. I was looking for some engine mods but i just skimmed right by it -- again sorry about the confusion.



Anyone have a 14 tooth fron sproclet for a 300ex??

[mxracer08]

no prob man