do any of you guys out there have a 400ex w/ an HMF full system? What is your main jet size? I put a 180 in on mine and it was sputtering a little at full throttle and occasionally back firing when i let off the throttle. Does this mean i am running too rich or too lean. Should i go up or down on the jetting? What is the dynojet equivalent of a 180 Keihin jet?

 

180 sounds too big.

I'm running a 165 dynojet with an e-series and K&N. Thinking about dropping to a 160.

Most people running a keihin jet are running around 155 with this set-up, give or take. Depends on elevation, temperature and other mods.

 

sounds like ur a little bit too rich, but keep in mind that slight backfireing and popping may be normal when going full throttle and letting off the gas. if its really bad then ur probobly rich.

 

try a Keihin 155 mainjet or around a 148 DJ.
if the bike is backfiring on deceleration, you need to turn your fuel screw out a little bit. try 1/2 turn or so for starters. if you need to go more than 1 full turn out, i would put in a larger slow jet.

 

im still learning so forgive me. but whats a slow jet?

 

Think he means pilot jet.

You might get away with a 148 DJ if you have a stock intake but that would be the only way. I wouldn't try one that small with the lid off or a vented lid. Better a little rich than a little lean.

 

a 142 DJ is equivalent to a stock 148 keihin jet.

yes, a slow jet is what everyone referrs to as a pilot jet. your stock one is a 38. most people just put in a 40 or 42 for easier starting.

 

You can't just compare the diameter on the two. They are different lengths.

 

Where is the fuel screw on the 400?

 

Adjust the one on the bottom of the carb. It's hard to get to without yanking the entire carb though.