Hi new to the forum. I bought a used 02 sportsman 400 recently. Owner put a brand new carb on it from polaris. It starts and idles perfect give it throttle and it bogs. The main jet is at highest volume for fuel to travel there are no obstructions in carb and i did check intake manifold for leaks. Float is also working fine. Heres the kicker if you take air filter off and slightly place some of your hand over air inlet to carb it revs to the moon like it should. Put air filter back on and button cover up back to bogging. Seems like it needs more vaccume or less air to carb. Please help w ideas!

 

Pull the fuel line from the carb and crank the engine over. Should be a steady stream of fuel. If fuel stream is weak,check for kinked/leaking impulse line from the carb to the fuel pump.Plus uyou can draw a vacuum on the impulse line with a mity vac.If you narrow it down to a fuel pump problem,they're 15 bucks on ebay. New Fuel Pump for Polaris Sportsman 600 500 400 Magnum 325 Outlaw 450 2520227 | eBay

 

I agree. I ordered new fuel pump last night and 3 way fuel valve. Will also replace lines and filter. Willlet u know what happens!

 

Yes fuel valves can stop up too over the years from dirt/trash along with the effects of ethanol fuel.Best that you do just replace lines, the valve and pump to eliminate fuel delivery as the cause of your problem.

 

Ok so i put new fuel pump on today w new filter and new lines. Still no new petcock in yet. Checked. Fuel lines no kinks new gas clean new carb vent for tank good cap loose as well start it up idling fine.no intake cracks or leaks. Take filter off and place hand restrict some of the air from intering carb and it revs up fine. All the lines from carb to pump are correct yes the fuel tank hass enough gas as well. New sparkplug to. Im stumped!!!!!!! Still boggs like 0 gas at 1/4 past throttle unless restrict airflow. Main jet is set all way up 4 as much gas possible.

 

If you don't have the air box and filter on install it as it will bog and hesitate from being too lean.Plus check that the new carb is jetted right to begin with. Should have a 167.5 main jet, 40 pilot, plus normally needle clip is on the 2nd or 3rd position from the top. Look over this parts break down.Dirt Cheap Yamaha, Polaris, Suzuki & Kawasaki OEM Parts & Accessories – Cycle Parts Warehouse Plus here's the pdf carb section from the manual,shows the the BST34 carb that you're supposed to have and settings on float,etc in case you're over looking something.https://www.google.com/url?sa=t&rct=...,d.aWw&cad=rja

 

Ok i will look at check the main again. Im pretty sure thats what size it was when i looked. I did run it with the filter on and cover same conclusion. The fuel petcock should be here today and that will be the last thing inline to change out. Old one was rough leaked if twisted wrong. Did get a little bit of old fuel line out of it as well. Two small chunks. I also have an extra carb from 02 500 sportsman that was suppsedly on it before. How it ran i dont know but i know the main jet was a 70 something. This sportsman used to be a an 02 500 rse as frame vin states but old owner put 400 motor in it as motor states on front.

 

Put the new fuel petcock on , all new gas lines, fuel pump. Still bogged past 1/4 throttle. Checked the airbox cover to make sure it had a good seal. Everything goo. Ended up duct taping 1/2 off airway at top of the snorkel that goes up under the tank andvthe atv runs great now all power is there. Does it possibly need a smaller main jet? Obviously its getting to much air

 

If you've had to shut down the air supply for it to run right usually means the carb is still jetted too lean on the main jet or float level could be off,shutting off fuel supply,or possible carb slide diaphragm or spring problem not letting the slide lift correctly,etc. You say it's a new carb,does it have the right carb for the 400 engine? Takes a BST34 while the original 02 Sportsman 500 engine that was in the frame takes a BST40.Different carb and jetting. Check the carb and jetting against the one shown for the Sportsman 400.Dirt Cheap Yamaha, Polaris, Suzuki & Kawasaki OEM Parts & Accessories – Cycle Parts Warehouse Here's the carb that's in the 500. Dirt Cheap Yamaha, Polaris, Suzuki & Kawasaki OEM Parts & Accessories – Cycle Parts Warehouse Plus was the stator and electronics from the 500 original engine used for the 400 engine replacement? They do show to have different part numbers. Could be part of the whole deal also?

 

My buddy has a sportsman 335 . I parked it on my trailer shut it off in drive gear still expected it to stay it place and it rolled 3 feet like it was in neutral. I put it in reverse gear w it off and it does same thing. Both my sportsman 500's will stay where they sit when in gear. Is this normal for a 335?