Attention 400 ex owners:

A friend of mine had a White Bros. rev box on his 400ex. He thought that something was wrong with it and so he sent it back to them. They assured him that the box was fine. Well, he put it back on and after getting his engine back from Trinity Racing (13:1 comp. 440, ported, etc.), it pulled like crazy low to mid, but just wouldn't run on top. Guess what! Looks like it was the rev box. He put the stock box on it and he believes it is running stronger even though he hasn't re-jetted yet. He is in the process of jetting it now, so we'll know for sure later today.

From what I've heard, the problem with the box is that is becomes stuck with a certain timing. It is supposed to vary the timing according to rpm, and the box has apparently become stuck with the timing advanced. I also heard that it can get stuck with the timing retarded.

Hope this info helps.

Daren