07 YZ450 and a Procircuit Pipe

Hey guys,

I have an 07 YZ450 and I am looking at buying a T-4 pipe from Procircuit. I called them and they recommend I run a 165 main, 42 pilot, NFPP needle in the 4 position from the top, and a 50 leak jet for this pipe. Does this sound correct? Right now I am running the 170/48 combo with everything else stock, and the bike runs great. I want more power from the pipe, but I don't want to mess up how well my bike runs from going to completely different jetting. My riding conditions are as follows:

Lucerne valley, CA

About 3000 above sea level

A lot of wide open throttle riding.

Any advice would be great appreciated. Thanks!

They have some reason for their recommendations, I would think. The 170 sounds biggish to begin with, and I've put pipes on 4-strokes that made them run rich enough on the pilot that I had to drop down a size. If they call for that, I would first run it with the new pipe jetted as is and see if it seems too fat. If so, or if you aren't sure, try it their way. You can always revert to your jetting if it works better.

Thanks for the info, I appreciate it. Would you opt for the slip on or the full exhaust system?

I have the full TI-4 system and I noticed the difference right away... Biggest improvement was on the top end - pulling longer, but I also noticed more bark off the bottom!

Thanks for the info, I appreciate it. Would you opt for the slip on or the full exhaust system?
For performance, it depends on the header included with the full system. If the length and diameter(s) of the header is identical to the stock header, there's no advantage to paying for the new one. This is generally not the case with performance full systems, however, and the gains and/or changes to the power curve can only be realized with the full set up.

Slip-ons offer very little to a YZ450 or a later 426 in the way of performance gains because the stock exhaust is, in fact, very good. The only real justification for a slip-on, IMO, is if you are looking for a quieter system. Otherwise, most of them are just bling.

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