I have a Bear Tracker 250 that I replaced the Mikuni carb on with one off of Amazon. I’ve adjusted idle and pilot jet (1.5 turns out). However, when I keep the airbox lid on and give it throttle, it cuts out. When I remove the air box lid it runs perfectly. I see that the standard main jet is a 95 but can’t confirm that from the old carb. The new carb came with 145, 150 and 160 jets. Think I need to run one of those so I can put lid back on? It’s a farm machine so just tempted to drill a few holes in the box and let it go. Thoughts?

 

Is there any reason why you adjusted the pilot jet to 1.5 turns out? I had a Yam 250 that came in with no pilot jet needle. Once I cleaned out the bright green fuel from the float chamber and blew through the jets, it ran and idled fine. If possible I would be adjusting the main jet needle. If you can't do that, try fitting the old main jet.