I just installed a Big Bore 440 on a 2002 400EX. I need to know a good starting point with the jetting. Is there anybody out there that can just give me an idea at where to start with main jet, pilot jet, air screw, and needle clip. Also I've been told that it is almost impossible to keep head gaskets in this quad, if that is true why do so many people do a big bore install? Is there something I can do to make this as painless as possible because I've already went to far to back out now?

 

I dont think the head gaskets are an issue like they were before. I've never had a problem with mine and it has plenty of time on it. I know a friend that had problems but that was do to bad machine work.

I'm not too much help with the Jetting.

DWT

 

check out this post. it will helpClick here

 

c'mon guys somebody out there has to be able to give me a starting point. I can get the quad to run with the choke on but it dies as soon as I turn it off, even just a little. I can't run it long enough to get a plug reading. I need a starting point so that I can get plug readings and adjust from there.

 

read the post above, but you are real lean on bottom or an intake leak if the choke/ which is actually enrichener . a choke has a butterfly that resticks the are aand forces it to move more fuel. but any way lower the clip, which raise the needle off the seat. gives more fuel. air screw should be 1 1/2 to 2 turns out

 

Do you have an aftermarket muffler? Is the air box opened up? Give those details, along with a guess at altitude, and I can get you close.

 

The muffler is an FMF & I am just trying to get it running without the airbox in my shop & I'll tackle that later. The altitude is around 600 feet.