hello fellow polaris people,

I was thinking about removing the airbox lid on the tb 250 and doing the airbox mod on the scram 400. Both of these machine are stock with only uni filters. The mainjet on the tb is 130 and 240 on the 400.
Has anyone done this to their stock machines? Any suggestions on jettings? I'm not looking big hp gains, just want to let the engines breathe a little easier, get a little better throttle response.

Thanks everone in advance, I won' tbe able to check in for a few days, but any advice is welcome.

 

I did the same mod to mine but also with a new pipe (200 scram 400) and I did have to rejet. Of course I live in the south and you in the north so I don't think I would be the best person to give you a starting point on your jetting. Hopefully someone from in or around your area will see your post and get you going in the right direction. I'm sure altitude may play a part in it also, so before you do what someone else has done, make sure you compare apples to apples with altitude in mind. There is a point also at which if you increase your main jet to a given size, you will need to add additional oil in the gas or suffer as I did out of ignorance and fry your rings. If you increase any one of the three things needed to make combustion, you need to increase the others proportionally, except in a 2-strokes case, that may include the premix also. You could just put in a new plug and take it for a spin and check the color after you're done and see where you need to go from there. I'm assuming you already know how to rejet and that you just want a starting point on main jet size and needle clip settings. Hope you get your answer and best of luck!