Does anyone have any experience with installing a 400EX carb on a 300EX? If so, what are your modifications, and the jetting that worked?

 

I'm thinking about doing the same thing. I posted this ? awhile back and the responses I got were good. The 35.5mm will fit the 300EX air boots, jetting I think will fall somewhere between a 400's and 300's jetting. I think stock jetting on a 400 is 152. The 300 is 122(mine was anyway). I think splitting the difference will give you a starting place. If anybody knows will a 38PE work on a stock 300 motor? I do have a Supertrapp IDS and K&N filter on it. Thanks, Mike.

 

it's a direct bolt-on. didn't even change the jetting. just added a few discs to exhaust, adjusted the idle mixture screw, removed airbox cover, and let her rip

pulls strong from idle - rev limiter

best part is it didn't cost me a dime, my buddy replaced his and it "found" it's way into my garage. go figure?

 

Are you referring to the 400EX carb? I am running a .080 overbore 10:5-1 piston, midrange cam, unlimited rev limiter, supertrapp exhaust, and stock airbox w/lid. I am looking for more power everywere, especially in the bottom to mid RPM range. I was also wondering if the head on a 300EX flows as well as a 400EX. If it does not, maybe the jetting should be richer?

 

yeah, OEM 400ex carb. throw it in, minor adjustments to lean slightly, and poof- runs great

it seems like you put alot of time and $ into your ex, but if your running all those mods with the stock carb, you missed something.

find yourself an air duct( airbox-carb ) from an old ATC350X, if you can borrow a carb from a 400ex that would be great, the object is to let in MORE AIR. more air, more fuel needed to obtain perfect 14:1 mixture,get it?

using a stock 300ex carb( properly set up for the bike, of course) and adding the 350X air duct, will require upping the main jet by 2 sizes. may also need to raise clip on needle a notch.

and a larger carb won't alter the power curve, it will improve throttle response. if your low to mid is hurting now, it will still seem soft until it gets on the cam. the cam does the curve.

hope i helped more than confused you with all of this. i tend to babble on sometimes but then again...............