z400 jetting problem

[z400rider03]

I just got a 2003 z400 and it has a yoshimura slip but it has stock jet. Whenver I try to give it gas it pops and bogs down. What should i do to fix? What size jet should I get?

[cataway]

it would be good to have more info .

is the air box lid on or off?

what is your elevation ?

any other mods done ?

[z400rider03]

I still have the airbox lid on and I live in new jersey so the elevation is about sea level. The only other engine mod that I know of is a k&n air filter

[cataway]

does it run worse with the lid off?

[z400rider03]

I haven't tried starting it without the lid

[z400rider03]

I haven't tried starting it without the lid

[joetracc]

I have the same issue. All I have is an HMF slip on, lid on stock air filter. I tryed taking the lid off and it was brutal. What jets will I need to fix the issue?

THX

Joe

[derekhonda]

You got to tell us what the plug looks like to be able to diagnose.

But in general, you are going to need a bigger jet. You see, your engine take fuel and air, does its thing, and then pushes it out the exhaust. Essentially with a modified pipe and with a better filter, you have more airflow into the engine, and more airflow back out the exhaust, but still the same amount of fuel. That is probably the problem you are experiencing, what you need to do first is tell us what the plug looks like.

[derekhonda]

Originally posted by joetracc
I have the same issue. All I have is an HMF slip on, lid on stock air filter. I tryed taking the lid off and it was brutal. What jets will I need to fix the issue?

THX

Joe

And then removing the lid creates an even bigger problem as now you have access to even more air.

[dw0095]

Originally posted by z400rider03
I just got a 2003 z400 and it has a yoshimura slip but it has stock jet. Whenver I try to give it gas it pops and bogs down. What should i do to fix? What size jet should I get?

Until you get your jet kit, try turning out your fuel screw a turn and half. (have to drill out the blank at the bottom the carb) will help with the bogging while revving up to about half throttle or so. But you will definately need to bump up to bigger jets with that exhaust.

for reference, I have a full hmf system and live in upstate NY (sea level).
160 main jet (dynojet)
3rd clip on needle (dynojet)
2.75 turns out fuel screw
stock pilot
high flow airfilter with prefilter, Lid off.

runs like a rabid raccoon, lol.

[z400rider03]

Ok thanks. would I be ok just getting a main jet?

[miles Machine]

you might be you can try it if you want id go with a 155 dyno jet jet or if your buying a mikuni jet which is more likely go with a 140 if you didnt know, the different kits like dyno jet use adapters with differently numbered and sized jets so be carefull of this. but i have a feeling you will need the aftermarket adjustable needle for the mid range which will be nice to have if you plan on doing any further mods to your Z.

[dw0095]

Best way if your beginning to mod is get a dynojet kit. comes with all different size main jets and adjustable needle. a little experimentation and you will get it right. Try a 150 main jet and needle on 3rd clip to start.

your mid and top end should run solid with that combo. the lower throttle is mainly controlled by your pilot and the fuel screw. if you don't bump up the pilot, turn the screw out a half a turn a time until it stops backfiring or bogging out.

Another trick is to turn the idle screw up and listen to the sound of the exhaust as you adjust the screw, the sound will be noticable when it's right.