Hello I'm having trouble with my 96 Polaris magnum 425. I got the bike after it had been sitting for years. I cleaned it up installed new belt and cleaned the carb and before I installed the air box I took it for a test run. It ran great. I installed the air box and ran it again and it bogged down on acceleration. It idles perfect. Very odd issue. I've adjusted the pilot screw any way possible (1,2 1/2,3,3 1/2 out) still nothing. I came to the conclusion that it must be something in the carb that messed up and I can't see it so I installed a new carb. Still has the same problem. I've even removed the air box from the hose that connects to the carb and just connected the hose and I've still got the same problem. The hose is definitely not collapsing either. I'm at a complete loss. Please help me

 

Check compression plus on these models check the exhaust lobe on the cam and valve clearance.If the lobe is beginning to wear down it can mimic carb problems.Most Polaris atvs won't run well without an air box and filter. Plus on Chinese carbs always take them apart and clean first plus check jetting against the oem Mikuni. Plus forgot to mention about pulling the black wire from the reverse limiter module on the terminal board. They all fail and it's really not needed and can cause limiting or dying problems. Plus you'll have full power in reverse without having to push the over ride button.Item #27(located above the cdi #43).

 

Ok I'll check the cam. Will a sheared flywheel key cause this issue as well. Like I said before it runs great With the air box off. Thanks for your help

 

If a flywheel key had sheared timing would be off and wouldn't run worth a flip with air box on or off.

 

Just disabled the reverse override and problem is still there. Inspected the camshaft lobes and they look great. Gonna check the compression tomorrow

 

Has anyone tinkered with the jetting? As OP stated most factory machines will run lean without the airbox, if your sure you really got the carb clean and all the little passages thru it, then perhaps the previous owner oversized the jets for more performance.....just a thought here..

 

Yes I cleaned the carb very well and it still bogged down which is why I installed a new carb and that has the same problem so I certain it's not a carb issue

 

Chinese carbs are tempting as the cost isn't much more than a good rebuilt kit for the oem Mikuni carb.The oem carb is way better than the knock offs.I'd get a good kit for it,don't just clean a carb and see if that helps. At least you can eliminate the carb and fuel supply if the pump is working ok. To test the pump just pull the fuel line from the carb and crank the engine over. Should be a steady or pulsing stream of fuel.

 

Yeah originally I got a factory carb rebuild kit and it did the same thing. That's when I decided to install a new carb. Do you think the valves being out of adjustment would cause this?

 

You can check valve clearance,.006 intake and exhaust but if that doesn't help I'd down load this free pdf service manual and go through the trouble shooting steps on the fuel system and also electrical trouble shooting checks and tests.https://www.google.com/url?sa=t&rct=...Z7Rqhg&cad=rja