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Stock jets on 400ex?

Old 04-08-2000, 10:54 AM
Range Rover
Join Date: Feb 2000
Posts: 169

If I have a wb pipe, wbrev kit, k&n filter running without the airbox lid at about 3000 Ft ele. would a 40 and a 165 be to great? I had it rejetted once but it was not a dealer and they couldn't remember what size they put in. I'm also running with all disks.
Old 04-08-2000, 11:00 AM
Weekend Warrior
Join Date: Apr 2000
Posts: 20

Do you use your choke? I completely removed the choke assy. That includes the butterfly inside, plugged off the hole with sealer, and used a K&N. It wanted more gas. I was able to run richer main jets, pilot jets. I bet with a pipe that would really make a difference. More air + more fuel = more power.
Old 04-08-2000, 11:03 AM
Weekend Warrior
Join Date: Apr 2000
Posts: 20

Don't forget to check the low side. If you just put around using less than half throttle for 5-10 minutes then check the plug. This will tell you what the low side is doing. It is just as easy to score if you are running too lean on the low side.
Old 04-09-2000, 06:19 AM
Pro Rider
Join Date: Sep 1999
Posts: 278

K&N makes a power kit for the 400EX which we installed today, makes quite a difference! Comes with the filter, sock, filter oil, cleaner, needle jet and assorted main jets. Instructions tell you what main jet to use by your elevation.
Old 04-09-2000, 10:47 AM
Weekend Warrior
Join Date: Feb 2000
Posts: 16

Does jetting the STOCK 400ex help starting? In cold or warm weather, or both? If I jet my carb, will my warranty be void? If i don't jet my carb could my engine wear faster?
Old 04-12-2017, 06:40 PM
Weekend Warrior
Join Date: Apr 2017
Posts: 4

Originally Posted by 86atc250r View Post
Actually, I would suggest everyone evaluate their stock jetting. Even in the owner's manual it states that the jetting is lean to appease the EPA. Lean jetting isn't good for power or engine life.
Hey im just got a 400ex all stock but runs a lil hot do u think i should move up jet size to a 150 anything else i should do?
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