I just purchased a FMF Power Core IV For my 400ex. They told me to replace the stock jet to a 152. Is this correct. I ride in Michigan at about 1,000 to 1,500 ft. Is this correct? Still too rich, or lean. The last thing I want is to screw this thing up and have to put a new engine in it. I also have a K&N air filter on it. Thanks, Scott

 

I also have a powercore IV pipe on my 400.
I ran a 150 jet I felt that the bike was running a little lean. A 152 may be just about right, run that jet for a while and keep a eye on your plug. The plug will tell the tale

[This message has been edited by 99exrider (edited 01-09-2000).]

 

Thanks for the info. How long should I run it before I check it? If anyone else has any more info about that jet I would still like to hear it. Too lean= white looking plug, too rich= crispy brown looing plug? Am I right in this statement?

 

I have am running a FMF Powercore IV-sa with a K&N filter w/outerwear and 1" holes drilled in the airbox lid. I also put in a Dynojet kit, I do not recommend this. My current settings for my carb (riding in IL w/elev. at 743 ft above) are as follows: Main jet--#160, low speed jet--#38 (stock), pilot screw--3.5 turns out, and needle--3rd slot. I have found this to be a real good combo. It produces a broad band of torque and helped the topend a little. I would suggest that instead of using a Dynojet kit, save the money and do the following: get a K&N filter w/outerwear, remove the airbox lid completely (if running in dry conditions), get a #160 main (and a richer and leaner jet for tuning), get a #40 pilot jet, turn pilot screw out about 1.5 to 2.5 tunrs (to get best overall performance), and raise your needle (lowering the clip the 4th hole from the top). Try this. It is alot cheaper than the Dynojet kit and should work better.

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a Fast Boy from Illinois -(FBI)- Riding a 2000 Honda 400EX

 

Hey Fly:
I have a 99 400EX with the PowerCore IV - and I spent alot of time trying to tune it just right.. 6 holes in the airbox/K&N - later UNI because it blocks fine dirt better - but I had prb with lots of different jet sizes from 150-165.. and pilot from 38 to 40 .. but it would still stall in 4th-5th gear - real bad.
Got the DynoJet - and it worked sweet first time. I talked to the guys at Dyno- and my local Honda dealer - they both told me the same thing- powerband and increase you will see is in the needle/and its clip position more than the jet.
Dyno has a different needle that ships with the kit - its narrower- and it makes a hell of a difference. I can peg-it in all gears-and it runs strong now. My buddy on his Warrior is not happy. He wasnt happy before - but now i pass him up in low 4th.
Im almost sea level - and ride in the desert alot - With the DYNO needle - i have a 170 main -40 pilot -and 2.5 turns on air/fuel mix. I monkey'ed alot with different jets/settings/removed the carb 5 times - and finally got it right with the DynoJet out of the box - should of saved my money in the beginning... Trial and error cost me days in tearing it up - and about 20+ dollars in jets/etc... I clocked my 400 now at a cool 70mph (fast).. with plenty more - if i ever got the WB black box!