Honda TRX ATV Forum banner
1 - 3 of 3 Posts

· Registered
Joined
·
8 Posts
Discussion Starter · #1 ·
Hi, I have a 2001 400ex and am curious about what size jetting to use. It has an 11:1 piston and a Lexx slip on muffler. I also will be running it without the airbox lid. I am also wondering If I need to use a higher octane fuel with the 11:1 piston or just regular gas.

Thanks
 

· Super Moderator
Joined
·
4,815 Posts
Welcome to the forum.

First; the TRX400EX was designed to be run on 93 octane from the factory - with the higher compression piston, 93 will still be adequate to use. I doubt you can find 93 octane at any pump, so the options are to run 91 octane non-ethanol or VP Racing SEF 94 octane.

Second; jetting is as individual as the set up - changing the exhaust does not require a jet change, but changes to the intake require changing the jets. Idle does not normally need to be rejetted, but people like to think that more gas is more power, so go up to a 37.5 pilot jet ans readjust the pilot screw to compensate for the richer idle mixture. Go up to about a 160 on the main jet, ride it or dyno it and adjust the size of the main jet for peak power at 10,000 rpm. The main jet is the only fuel control when the engine is running at WOT. Anything between 1/8 and 3/4 throttle the fuel mixture is controlled by the slide needle and needle jet. If the engine surges at 1/2 throttle holding at a steady speed, then raise the needle to richen the fuel entering the air stream - if the engine blubbers like the choke is on, then lower the needle to lean the mixture. All assessments to jetting have to be done with the engine a full operating temperature (ride for 15 to 20 minutes before making changes) and the ambient air temperature should be about 70 to 80 degrees F.

Have fun learning how to jet a carburetor for maximum performance.
 
1 - 3 of 3 Posts
Top