180 main with just a K&N air filter and no lid! !????

[whyzee]

Decided to add a new K&N air filter and rejet. For fun I decided to remove the air box lid also. I have pretty good knowledge about jetting but being new to the 400ex motor I did some research about where to start. So I started with a 155 main stock needle clip etc.
Ran great. Tremendous power increase. Being afraid of running lean I immediatly went to a 160. Ran awesome. Again ran great, actually could almost pull 3rd gear out of my corners.
so I went up and up.....all the way to 185!!!! Finally started to feel the motor choking a litter.
Went down to a 180 main, runs incredible. The power increase over stock is so much that I am afraid it is too much for my motor. I do not want to blow it up.
anyone else wind up with jetting similar to this?
Stock exhaust by the way. Air temp was 55 sea level elevation.
Thanks

[CJM]

Did you look at the plug?

For that elevation and setup a 160 is about the highest you would want to go. With all my mods I run a 172

[CJM]

This is what your plug should look like (its actually mine)

[SpasticR450]

For me No air box at all, k&n and a slip on needed 165

[fearlessfred]

Originally posted by CJM
This is what your plug should look like (its actually mine) cjm is correct when suggesting reading the plug,but i would go a little further and suggest reading the plug after running thru the gears wide open pulling the clutch in and shutting the ign off at the same then read the the plug.this is how you will get a true reading for the main jet http://members.uia.net/pkelley2/sparkplugreading.html this is just one of many sites that will show you how to read plugs

[whyzee]

Yea, I didn't have a spare plug to do the chop test with. For ha ha I put the air box cover back on and it would hardly run after half throttle. I know the jetting is nearly spot on at the 180 main but I just can't believe it. Will do plug chop this weekend.
Thanks for the replies. Keep em coming.