Air box mod

A few weeks ago I cut the baffle out of the air box lid, and also the rear of the opening so it's now straight across(instead of concave) to try and get a bit more flow. I also cut down the lip around the opening on the sides and rear of the opening for more clearance from the seat base, and cut two one inch dia. holes in the left number panel. Since I only get to ride a couple times a month(if I'm lucky), I wasn't able to test my work right away. But I swear it feels richer now. I dropped the needle one position to help clean up the now increased low end bog. It helped some, but I'm perplexed. Could Yamaha's army of engineers know more than a hops and barley propelled hack saw operator? Seriously though, I'm wondering if my quest for air flow didn't just cause more turbulent air flow, or :). Has anyone had similar experiences? I guess I could buy a new air box lid and test them back to back. Or should I open up the rear of the air box also? What do you think?


have you though about dropping your pilot a size or two? Is 45 the stock size for the WR450? I believe I'm running a 42 in my 426, and I've never had any problems with the low end (I've done all the freebie mods too). You might wanna go to a leaner pilot, or at least lean out (turn out) your fuel screw. While the needle will help a little bit, I'm pretty sure it has the most effect from 1/8 - 3/4 throttle. The pilot jet is really what's going to help you at low end (from closed throttle to 1/4) Let us know how that works out for you.

or at least lean out (turn out) your fuel screw

Turning out your fuel screw richens, turning in leans.

MadMan- Yeah,45pj is stock, I was running a 48 with the stock needle, which worked better, but had to go back to a 45 with the JD needle. I haven't worked on re-jetting much yet though, because I'm trying to figure out whats going on with my air box mod. I was hoping to increase air flow by chopping on the air box lid, which would result in the need for richer jetting, if any. It seems like I've back peddled a bit.

I've seen where guys have done various mods on theirs. Can anyone tell me what your results were from your work? Did you get noticable improvements? Enough to require richer jetting? Has anyone noticed results similar to mine, especially on the bottom?

:):D :D

I doubt you screwed anything up by modifying the air box. Jetting the Yamahas is never easy. Try the JD blue needle and see if that helps your lower throttle opening response. :)

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