I am getting ready to start building this thing and wanted to know if anyone out there can offer some advice.Im putting a XR600R into a 400EX frame.Any help would be great thanks.

 

lot's of time and effort, get ready. I've done a XR650L in a Warrior frame, but am about to put one in my ex frame as well, should be a little easier I think.
I chose the 650 for the electric start, it's basically the same engine, and all parts will interchange.
I'm just not willing to kick-start one of these built monsters, stock maybe, but the stocker will not even hang with a 400 with a pipe, you have to build these motors up to run, their made for dodging trees on trails in stock form (33H/P)

 

Screw it buy a 450!!!!!!!!!!!

 

some people don't have 7000 dollars to spend

 

If it had to do with money then I would buy a 450.See with a big bore kit put in it its a 660 and with the bore kit and a custom stroker it is over 700.So as you can see with those mods and a full on race suspension it cant be about cost.Cuz you can see it will cost more than a 450.It is all about the big bore motor.