do i need to rejet

[trailblazin joe]

I will be installing the HMF sport series slip on for the Z-400 and was wondering if I would need to rejet. I will also be putting on the UNI oil filter with an outerwears airbox lid.

[drzoo2]

Absolutely!

[TRXRIDER4567]

what about just a fmf slip on.

[drzoo2]

Iffy on just a slip on. If you increase your airflow then you need more fuel. I would think you'd need to bump up one size on the main.

z

[YFZ450Ridr]

deffently rejet, even with only a slip on. you might be able to get away without rejetting with just a slip on but you wont see all the power you have available, plus it wont run very good.

[trailblazin joe]

Would the recommendation be to go up one size off of the stock or would I be able to go up two sizes?

[drzoo2]

Are you just adding a slip-on or are you taking the airbox lid off also. Removing the airbox lid like in your original post WILL require a jet change.

Stock jetting is a 130 Mikuni Main. With just a slipon I'd jump to a 135-140. If your removing the cover with a slip-on you'll need atleast a 145-155. All this depends on elevation and every bike is a little different. These are only ballpark. Doing both mods may also require you to adjust the fuel screw. You may run a bit lean at idle and off idle.

I have a K&N airbox lid with a full exhaust and am currently running a 150DJ main which runs a little smaller than the Mikuni at the same #. I also have the Alba adjustable needle. I've seen other people have mains as large a 165 or 170 so there is variation. I can only give approximate recommendations. Jetting requires tuning to your specific bike. I know my jetting is close because any larger main and I get a rich hesitation. A fully open airbox may jump me up a point or two but I ride in some dusty conditions so I like the added filtration from the K&N lid. I have to clean this about every other ride vs the filter.

z