2001 325 Magnum Sputtering Problem
I have a 2001 Magnum 325 4X4 that started running real bad last year. I was sure it was a carb problem. I replaced several parts, including the diaphram that was ruined from running excess cleaner in the gas. I got the motor running real good. Recently I was pulling a heavy load in low gear at a slow speed and all the sudden lost power. I disconnected the load and was barely able to run the atv into my shop. The engine was sputtering real bad and backfired some. I took the carb off and could not find anything wrong. Put it back together and had same problem. I then bought a carb repair kit and replaced all the needles, after making sure there was no dirt or blockages in the carb. I also put on a new fuel pump and fuel filter, and completely flushed the fuel system. Put it back together, and fired up. SAME PROBLEM!!! I have also adjusted the valves (last year) and checked the compression (good). Motor starts right off. I have noticed that the diaphragm slide valve does not go up when I try to rev the motor. When I lift it the motor starts to sputter real bad. I'm pretty sure I have all the parts in the carb installed correctly, per the diagram. I can sure use some help.

 

If the diaphragm is ok,needle is installed correctly in the slide(clip and plastic hold down parts are correctly installed) along with the spring,the engine vacuum should be able to lift the slide properly.Problem could still be in the carb or you're over looking something. Unplug the black wire from the limiter module and see if that's the cause of the sputtering/limiting problem. Item #35 on the parts break down.Dirt Cheap Yamaha, Polaris, Suzuki & Kawasaki OEM Parts & Accessories – Cycle Parts Warehouse

 

I pulled the black wire as suggested and it made no difference.
I didn't note in my first post, but I'm seeing quire a bit of black oil residue in the exhaust and on the plug. I've had this for awhile, but I can't imagine that this would cause the sputtering all-of-the-sudden.
I'm leaving after I post this on a fishing trip. Probably will not be back on the atv project until Sunday evening.
Thanks for helping.

 

Think I'd do another compression check or even a leak down test and see what you come up with.Shouldn't be oil in the exhaust unless piston/rings are worn letting oil get into the combustion chamber. That can cause it to spit and sputter for sure.

 

What should the compression be, and how is a leak down test conducted?

 

Manual shows compression to be between 70-90 psi on average. This is because of the compression release lever on the cam that holds the exhaust valve open a little making cranking easier.Item #9.Dirt Cheap Yamaha, Polaris, Suzuki & Kawasaki OEM Parts & Accessories – Cycle Parts Warehouse If the detent lever is not working properly it possibly can be causing problems also. If must be able to flip over and back easily.Check that the spring ears aren't broken either that tension the detent lever. Leak down test on a four stroke can tell the condition of the valves and rings.Most manuals allow a max of 15%-20% leakage,but I'm not too crazy about that much. On intake and exhaust valves you can hear air hiss through the back of the carb or muffler if excessive.Usually on rings leakage you can hear air hiss in the air box where the crank case vent leads to.You can even remove the dip stick and see if oil bubbles. Here's a general video on this. Cheap leak down testers are at Harbor Freight,Northern Tool,etc.