To review: stock 400EX HMF slip-on exhaust and K&N air-filter and I just re-jetted from the stock 148 to a 152

Welp....just fired it up and took it for a test spin. Fires-up just fine, idles really nice. Low-end & mid have a really smooth & nice pull...BIG-TIME difference from stock. Everything feels great with a noticable improvement...up until I go WOT and try to wind it out.

I put it in 2nd and pulled the throttle wide-open...it went from idle all the way to about 85% wound-out, but then it starts to hesitate & "stumble" and it won't wind-out all the way. Again, the low & mid are great, but once I get towards the top-end it just doesn't want to wind out. I'm guessing lack of fuel and I need to jet-up to a higher number????

Hmmmm....

Originally posted by zrpilot
Start with the biggest numbered main jet and run at wide open throttle, the engine should stumble at wide open throttle. Install the next smaller size until the stumble is gone.
Reading this, it sounds like I've got to large a jet? cause I still have some "stumble" at WOT. Ya know, the air-filter instructions say I should remove the air-box lid. I did not do this yet, maybe that would make the difference? I'm still pulling air through that elongated snorkel...removing the lid should provide more air, so if I'm over-jetted and running rich, the additional air (or ease of air, eh?) might compensate for this. Am I on the right trail??

Dude....THANKS!