600 sportsman runs great with air filter box off. as soon as box put on it breaks down at about 1/2 throtle, it sputters and back fires. put in shop replaced cdi, stator, coil, rebuilt carb, new fuel pump, and sent back said couldnt figure it out. any ideas.

 

Replaced the stator,cdi and coil with what brand parts? Plus air box on and it bogs normally is because of a carb problem but still can be an electrical problem.

 

not sure brand was done at shop, had car mechanic look at he thinks its jetting, but he thought to ruch, so jetted it down, made it worse, was going to try larger jet, currently has 150 in it.

 

Stock jetting was a 45 pilot jet and a 155 main jet(before 10/2/03) a 157.5 after 10/2/03. Main thing is that you do have the separate cdi and coil and not the early model 600 that had the Ducati ignition with the combination coil/cdi. I'd go ahead and jump up to the 157.5 as there isn't a heck of a lot of difference between it and the 155 and go from there. Polaris machines are jetted with the air box and filter installed.If you have decent compression,125 psi or more,have good spark,go into the carb first. You can get Mikuni jets at most area dealers or online.https://jetsrus.com/a_jets_by_carbur..._selection.htm

 

thx will try that, its newer ignition

 

put in 170 jet is better but still breaks down half throttle with air box on, any other ideas

 

Again I'm making sure you have the air box and filter on when this happens! Plus make sure the foam collar on the air box intake tube isn't blocking air flow.If you have to go that rich on the main jet to make it run better then somethings not right either in the carb(that the shop rebuilt) or you have an electrical problem. One simple test that might work is a timing light that old techs used to see if it is an electrical problem. If the light stays constant when the engine starts breaking down,then it's probably not an electrical problem. If the timing light flashes in rhythm with the miss or bog,then fairly sure it's an electrical problem. Here's the pdf section on carbs from the manual. It goes into good detail on the BST34 carb that you have on rebuilding along with setting the float height correctly. Plus if you have to go back into the carb make sure all orifices and jets are clean and open with an air gun if you have a compressor or carb spray with a straw.https://www.google.com/url?sa=t&rct=...U2gGlaHJWSIlbA If you need a manual,here's one for 5 bucks that can help on electrical trouble shootng if it comes down to that.2004 Polaris Sportsman 600 Service Manual PDF Download

 

Can you pull the plug after this 1/2 throttle breakdown and post the pic? As you move to 1/2 throttle you really come on to the needle jet and come off the idle circuit (pilots)...so I'm curious what your needle setting is if adjustable. I'd also make sure it's installed correctly (you'd be surprised with that one).


Another area overlooked is the choke circuit...


I'm guessing it's running very rich...since putting on an airbox will most certainly restrict airflow.


Not sure how this is electrical if it runs fine with the airbox off...but ya neva know...