I have a 2001 Trail Boss 325 that I bought as a basket case. The first thing I bought was a factory service manual. It ran only if you sprayed starter fluid down the carb and briefly. The carb was a mess and I rebuilt it. per specs. I did not touch anything internally on the engine.
It now starts fine and idles like a clock. It drives around a low speed very nice but, when I go to speed up on the road the engine brakes down at the mid to higher RPM. Like a bad plug or not enough fuel. I put in a new plug and have the same results. It almost feels electronic but, I'm not ruling out fuel. I flushed the gas tank, replaced the fuel selector valve and fuel lines, filter ext. I did not test or touch the fuel pump during the overhaul. I'm scratching my head. Any ideas out there would be greatly appreciated.
Cheers,

 

Welcome to the forums.

When you cleaned the carb, what setting (clip) did you use on the needle?

 

You can test the fuel pump by pulling the fuel line from the carb and cranking the engine over. Should be a pulse of fuel from the line if the pump is doing it's job. You can also pull the black wire from the reverse limiter and see if this is causing the limiting problem.Located under the front panel,far left. Item #18. Dirt Cheap Yamaha, Honda, Arctic Cat & Polaris OEM Parts & Accessories – Cycle Parts Warehouse If none of this helps,and you think it may be an electrical problem,best to have a manual for trouble shooting and resistance tests.Can't find a free one. Here's one for 15 bucks.http://www.ebay.com/itm/2001-POLARIS-TRAIL-BOSS-325-4X2-ATV-REPAIR-MANUAL-/351146884998?pt=Motors_Manuals_Literature&hash=item51c1fc3f86&vxp=mtr OR a hard cover shop manual like I used for 35 bucks.http://www.ebay.com/itm/Polaris-ATV-2001-Trail-Boss-2X4-325-Shop-Repair-Service-Manual-9916584-/271584104851?pt=Motors_Manuals_Literature&hash=item3f3bac9193&vxp=mtr

 

I forgot to mention that I dropped the main jet needle down notch because the plug was a bit on the dark side. I will do the fuel pump and rev overspeed test. Yes I have the factory shop service manual. I'll let you know the results.

 

My 325 Magnum used to act like that intermittently, took me a lot of plastic removals to find it, but the wires from the stator that run up along the fins on the jug just happened to have rubbed through on the impluse wire from the ignition and would ground it out when i gave it throttle and the motor would move in the mounts....I was ready to put a bullet in it until I finally found it.

 

Thank you I will check that. I'll bet you are good at taking the plastic on and off

 

I had a similar problem with a scrambler. At about half throttle and above it ran very bogged down.

It ended up being the reverse override switch was bad and it was kicking on when going forward for some reason. One possibility is that brake fluid leaks from the resovior onto it

 

OK thanks I'll check it out