Did anyone just put a bigger bore into their ex and nothing else? OR does it require putting new valves, cam and all that other stuff to make it run like a 440?
The problem is my boyfriend and I just put a 440 Wiseco piston in his 1999 400ex and he has tried and tried rejetting that thing to make it faster. My 2001 400ex can keep up with it. We have put anywheres from a 168-185 jet in it and tried raising and lowering the needle and also putting in a smaller pilot jet. So what does he need to do to make this thing beat a raptor?
Thanks for your help in advance.

 

Make it a 650!! No not really. My friend has a 440 kit in his bike and the thing hauls @#$! He started with just the over bore then built up from there. The biggest improvement he made was making the motor breath better by using a K&N with no lid on the air box, he then installed an Edelbrock carb and White Bros E-Series slip on. The head remains stock as does the cam and valves. On a track Raptors can't keep up, but on a long straight away they will catch him. Hope this helps.

 

Does he have on a K&N yet? If hes breathing in good, try for a slip on pipe, if money is an issue(is in my case). Has he noticed a difference in the power? he should notice a ton, I did, and once you know its there, you can strat messing around with gearing. Right now, you both are geared the same, but with the stock cam and an overbore, you probably created a low-end monster. The aftermarket cams get you out of that, but for now, I'd try bumping up your front sprocket a tooth, or the back down a tooth or three. This will decrease the ability to wheelie(low end torque), and increase overall topend (topspeed) but, I'm guessing you have bottom end power to spare now, doesnt he? Good luck. (By the way, my 440 as listed below has the Dynojet kit in it, with a 170 Main jet in it, jetted per the Dynojet instructions included in the kit. Very reliable)

 

I guess I should have told you that he has the new Big Gunn full exhaust. Maybe that could be the problem?? Also, He has tried that thing with the air filter (putting tape over the filter). He's the one should be posting this stuff. He knows what is going on. The quad seems like it only wants to be ridden on the back two wheels. It does wheelies real well, so don't think that is a problem. Thanks for all of the input.

 

If it was me I would try some main jets lower than 168. Keihin jets are much richer than Dynojet. So it can be kind of tricky to tell what jetting to use.

Another thing is I am not sure that the Big Gun is much of an improvement over stock.

Adam Smith

99 400EX