300ex questions

[cbrooks118]

I am a new user with a question about a 93' 300ex i traded some dunebuggy parts....but i have soem questions about it if someone would be kind enough to take the time. It runs, but it smokes...doesnt idle right, i was going to clean the carb, but the genuises who had it before me stripped the screws.... Should I Bore the Motor, put slightly larger piston, or just start with replacing valves? My wife will be riding this bike, but i kind of want her to able to keep up with us on the bigger bikes. We mostly ride riverbeds, and occassionally make it up the Little Sahara. I read previous post saying the 300 ex sucks in the sand with paddles on... Already started with some mods to it to bring it back to life, front wheel spacers, went through greased and checked everything, oh and i took off the balloon tires and went with rzrs 20x11x9's.. would be apprecaitive to anyone who has advice on motor!

[Pvt. Maggot]

Well if your going to be looking for more power, and its already smoking, Give her a new top end. Do you know if its stock bore or not? When I had my 300 I ran a 40 over 11:1 piston with a port and polished head, and it had tons of power. I didn't change the cam and was running stock valves. They are peppy little motors, Just freshen the motor up and you'll be good to go, and if you don't feel like messing with the stripped screws in that carb, you could always upgrade to a 400ex carb, or buy another 300 carb. Good luck with your bike

[cbrooks118]

it is a stock bore-- should i go .020 over, or .050 over?

[Sjorge450R]

Originally posted by cbrooks118
it is a stock bore-- should i go .020 over, or .050 over?

you wont notice a difference between the two if they are both high comp pistons. You will notice changing from a stock comp to high comp tho. and for the sand, I heard that people say to use the 6 paddle tires.

[Cody_300ex]

Go with a .080 over 11:1 piston

[Sjorge450R]

Originally posted by Cody_300ex
Go with a .080 over 11:1 piston


the only bad thing about the .080 over is that it is the highest you can go on a stock bore while staying under 300cc. And when i talked to GT Thunder and Hetrick racing they both said you will notice a difference when going to 11:1 but you will not notice a differnce from going to .02-.08

[bmf400ex]

you first need to find out why its smoking before you go dumping money into the engine. is the smoke white, black, blue? take off the carburetor, take vise grips and get those screws off. clean it good with gumout, identify the size of pilot and main jet. check fuel line for cracks, as well as intake boot on carburetor. stock pilot jet is 38, stock main is 122. start there and get it running right, they are known for blowing a bit of white smoke when its cold in the winter.

if you want more power don't bother with a bore of any size, go with a high comp piston, camshaft(with upper rpm gain) and get the head ported. the head is whats most restrictive. do you think your wife could handle any more power? you may not need to spend any money on it...

[cbrooks118]

well, it smokes white since i had it, doesnt run smooth has like a tick in it... got online at rocky mt atv and was suprised to find new wiseco piston .020 aqnd gasket kit was only like $95... So i went ahead and ordered it -called local machine shop and they said they could bore the jugg and hone in piston for 54.95-- I am looking for another carb right now on ebay, since i want to put twist throttle on it....Another question though, i have had replies telling me to put 400 ex carb on it---what will i need to do to dial this in? Figured new piston and gasket job would hurt nothing on a 13 yr old bike---Port and polish seems to be to much $$$ when i could spend it on an aftermarket exhaust! thanks for your input, overnight this has become my new favorite site!

[cbrooks118]

oh yeah the wiseco is a high comp 11:1

[Sjorge450R]

supposebly, the 400ex carb with stock jetting works pefect on slightely modded engines. All you need is the carb and a 350x air boot. Im not sure if the throattle cables are interchangable.