Ok guys. Been tinkering on this thing for a while now (2002 Polaris Scrambler 400). Seems as I get one issue fixed another pops up. I rebuilt the top end with OPT'S guidance. A big thanks to him for all his help. water pump shaft started leaking shortly after that. Front pads wore out not to much longer past the water pump fix..... and so on.

The issue I am finding now that we are finally riding it again is that it idles good. Starts right up, revs good in nuetral. It seems be starving for fuel when riding it. Not bad, but enough of a miss that I notice it. I marked the stater position when I removed it so I dont think timing is an issue. Reeds are new. Ive been running 93 octane since the top end rebuild. (the kit we ended up with was 83.94 piston and rings, not sure how much over stock that is). Also it seems to run great with the air cleaner off of it.... Could use some advice on what to adjust from here.

Thanks in advance

 

If it runs better with the air cleaner off,then you're running too rich on the main jet.Air cleaner's not allowing enough air supply to fuel ratio. Std main jet is a 240 depending on altitude/temp. On some I've had to drop the main a size or two even with aftermarket pipes,etc. I always thought the Scrambler 400 was jetted too rich to begin with as most all the other 400s were in the 200-210 main jet range and even some of them I had to drop for slow poking farmers/ranchers. You can also play with the jet needle position(lower it),but don't think it will allow enough wiggle room.Always do a plug chop when changing jets to make sure the plug is a light to medium brown color.Plus not necessary to run 93 octane. 87,89 octane is fine in most cases unless you bumped up compression and in some cases high octane can make them run a little crappy. Found that out on the little youth machines real quick.

 

When u say jet needle..... U are referring to the small flat head screw on the outside of the carb? Correct? If so I have it only 1.5 turns out, is it safe to go in any further?

 

he's referring to the needle that goes through the carb. there is a clip on it and groves when you can raise and lower the clip on the needle to change settings.

 

Thanks guys, I dropped the needle down last night in a couple of different positions. Adjusted the large idle screw and had the small screw at 1.5 out. Idle was great, but I had a bad bog in both positions at low throttle. Any thoughts????

 

What main jet do you have?? If it still runs best with the air box off,then it's jetted too rich.

 

It's a 240. Never been changed as far as I know

 

Get a few size lower jets,230,220,210 and give it a try. Replace the air box and filter also.At least you'll know pretty quick if you're going the right direction on jetting.

 

sometimes running an after market filter like a k&n filter is like doing a jet change one size as air is more free flowing, but doesn't filter dust and other fine particles out. keep reading your spark plug as well when you do these changes to make sure your not going to rich or lean for sure. imo.

 

Thanks guys for the help. I ordered a few jets and a new filter tonight. No one locally had anything for something that old!!! I have a fear of running this thing to lean like the last owner did. The piston was very worn on the exhaust side when we pulled it apart for the rebuild. Im still new to 2 strokes and learning slowly.