OK can someone help me out, this one has me scratching my head...
I have a 2002 Sportsman 500HO That idles great and will run awesome for a few seconds then bogs like it is running out of fuel. I will stab the throttle and it takes off like a rocket and all is good but then it feels like it runs out of fuel and falls on its face so i have to come to a stop. Let it idle for 15 seconds and and it is good for another 15-30 second run and then it starts to stumble again. Doesnt feel like spark is cutting out, feels like it runs out of gas. Things I have done:

Brand new carb
Checked and set float level in new carb
New spark plug
New fuel pump
Loosening fuel cap doesnt make a difference (thinking maybe a vent issue)

Any ideas?

 

After market Chinese carb? If so that may be part of it. You should be able to pull the fuel line from the carb and crank the engine over. Should be a steady or pulsing stream of fuel. If so you can eliminate fuel supply.

 

Yeah it is a $50 carb off Amazon

 

Hopefully you have the correct replacement Chinese knock off BST40 carb and not the BST34 used on earlier models. Has the float assy that holds the needle valve in place. I'd still check fuel flow first and make sure you have good spark.Another thing to check is that you have the pump lines hooked up correctly. If it has good flow to the carb, remove the float bowl and check the jets. See if they're the same size of the oem carb plus you may have to remove the main and pilot jet to make sure they're clean. Check that the float isn't sticking and blow out all passage ways. People have found trash/dirt in some of these carbs along with metal filings.On some carbs the jets were different,on others they weren't even marked.That may be all you need to do. If it still runs crappy I'd at least rebuild the better oem Mikuni carb and eliminate it as a problem area.Probably wouldn't hurt to check valve clearance if you haven't already. .006 intake and exhaust.https://www.ebay.com/itm/New-Shindy-...ZRw15S&vxp=mtr

 

Thanks! Since it was brand new I never thought it could still be my problem, I will tear back into it tonight.

 

I bought a Caltric carb from Amazon. worked right out of the box but was flooding so I had to adjust the float a bit... Check your float height and make sure its right.
Also make sure there is no binding in the float assembly,they are close to a bst40 but not identical.

 

Well thanks guys, that was totally it. Tore into the first amazon carb and just couldn't find anything wrong. Everything was "clear" visually and even sprayed it all down good with cleaner and air but did not help. Even took the jets from the Mikuni and no help.

Bought a Caltric off Amazon, adjusted the float and wouldn't you know, running better than new now! I never would have thought that the first "new" carb i used was bad out of the box so I owe it to you guys, thank you so much!

 

The knock offs are a crap shoot, Glad it worked out for you!

 

The knock offs are crap. Glad it worked out for you too!

 

Well based on your findings I'll half heartedly recommend the Caltric brand as the only aftermarket carb to get. That is after you clean it first and set the float level..