i have a question as to which main jet i should be using in my z400 . i have opened up the air box installed an after market air filter ,the carb is stock with a Dyna kit and a 142.5 main jet the muffler is stock but i did replace the cap with opened up one. and i put on a higher rev limiter. i did try a 150 main but it was just to rich and the only one i could get that was smaller was the 142.5 . for the most part i will be running below 1400 feet and just trail riding or hotdoging it at the dunes. is the 142.5 the best jet for my setup ,would a 145 be better?

 

I run a HMF pipe on my 03 z400 with k&n power lid and K&n filter. I would suggest this pipe if your looking for more power. I put it on last summer and couldn't beleive the extra power it gave me. They have pretty decent links in the hmf forums for jetting, but when i did mine i was up to a 200 jet and it still ran fine and plug looked good.I called hmf for tech advice, and they said i should be at about 155 main. The fact is the main jet on a four stroke doesn't change your performance nearly as much as a 2 stroke. You have to make sure your setting the fuel mixtrure screw on the bottom of the carb while its running at idle. Its a pain to get to, but necessary to adjust for the bike to run good at all ranges in the rpm. P.S. If your interested in the pipe, join hmf forum first, and you get a $20 discount with a new purchase.

 

i find this very hard to believe not the muff part but your using a 200 jet maybe you should say what other mods you have done.

 

No other mods, I did put in the 155 jet after i talked to the tech at hmf. I was concerned when i got up to the 200 size jet that i was going to lose good gas mileage. But as far as running good, I did the choke test in low, midrange and high speed circuits for the carb, and it still ran fine, and the plug looked good after every jump up in jet size. Maybe it would have run bad in different weather conditions, but i was tuning at 70 Deg. F. with very low humidity(spring time) 800 ft. above sea level. I did bump my idle jet up one half size also. I think it was 22.5 stock, and went to 25 jet. The K&N power lid was fairly new at the time so i couldn't get any solid jet ideas from anyone yet, nobody in the tech places i talked to had used them yet(Alba and HMF) . But it runs great winter thru summer now. A lot more power for silver lake dunes, before I was underpowered stock to climb the steep hills without a long run at them.

 

i under stand that a pipe will make a difference but its just not necessary for me ,if i got one for free yeah I'd put it on but i have nothing to prove and no ego to please. so your running a stock carb with a 155 jet .but i have a Dyna kit in my carb I'm a summing the different needle and jets are making up the difference tho the muff no doubt is also a fat tor. it makes me wonder what the Dina charts show on this