I have heard that a 400ex carb will work well on a 300ex. I have a Cobra exhaust on it, with an aftermarket filter, that is the only mods I have done to it, I need to put a carb on it, & I was thinking of putting a 400ex carb on it. Would appreciate any input on this. Thanks

 

with the mods you have I don't think it would work. if you did get it to work you would loss power compared to stock.Now if you port the head and add a cam and get a real pipe it might be a nice add on. Peace Sick

 

Thanks for the input, I was figuring I was going to go back with a 300ex carb. This is my son's atv, I really want to keep the $'s down on it, because he most likely will be on a 400ex within a year or so.