Hello all, I am new to this forum, and am in need of some assistance on diagnosing a 550 mule. The problem is this, after driving and warming up, the engine slows down to idle. This will happen in gear or in neutral. For example, in neutral, if you hold the throttle wide open for about 2 minutes, the engine slows down to idle speed and thenrevs back up. New spark plug, new ignition coil, cleaned carb twice, new fuel filter and hoses, new electric fuel pump. I have installed a bypass type filter and still same problem...Sorry for the long post, but any help or advice would be appreciated.... thanks

 

Not sure on that one, but if it has been run with old old or fuel there may be build up on the valves where they pass through the guides. If this heats up it may momentary cause the valves to stick causing problems with running. I had a 550 that a customer never serviced. They could drive it all day long normal, but when they got out running it hard it would stall for a sec and start right back up. Finally linked it tot he valve sticking and loosing compression. When it could for a sec the valve would close and start again.
If your tank has some loose debris, it could be restricting the tube that lays along the bottom and the pump can't supply fuel causing a power down situation also. In your case it sounds more fuel than electrical.