Regarding 4 stroke jetting:

We had a 1998 450ES in our family with a Supertrapp muffler. In the winter at at 0-10 degrees it definitely required rejetting. The rubber mounts melted off the muffler and the top MPH dropped by 9 MPH because it was too lean.
Now it did not seize but it was too lean as indicated by the speed and operating temperatures.

Final outcome? Removed the Supertrapp and went back to the stock Honda jetting. The Honda engineers did not leave much room for power increases on a 450 engine. Anybody who tells you differently has a vested interest in parts and modifications.

Bill, your 400 should run fine without rejetting with your stock pipe. Never had any problems on our two strokes running in the U.P. An air screw/choke adjustment may be required if it is difficult to start.

P.S. for optimal performance and efficiency my 78 Chevy requires different off-idle circuit and choke adjustments in winter vs. summer.

 

If you check with your polaris dealer you will find out that some of the 2000 scramblers have been seizing with factory jetting the problem is the neeedle setting HPD told me to use a half clip.They will seize just off the bottom and if you have your jetting right you will need to rejet for winter no matter what mods you have done .

 

Hello Blakely,

I have a friend who is a Polaris dealer. He recommended to me to use a 230 jet in a 1999 Xplorer 400 if I installed a K&N Air filter.

Result? Engine ran rich and sluggish, it did not need the 230 jet. This is Polaris's way of protecting themselves from warranty claims. It seems that too many people are installing the pipes, air filters, and jetting toward maximum all out performance and increasing their warranty expense. So...

Remember, your two stroke will run the fastest it ever did, right before it seizes.

 

Thor,
Thanks for the advice.I also have a KN air filter to.I did richen up the air screw allready.The quad really starts good when cold to,
Bill