I have a 92 yamaha waverunner111 650. I was pulling a tube at half throttle when the engine started acting funny. It started running rough even at full throttle. It doesn't have the same get up and go. I checked the gas and oil added more gas and oil was ok. Took it out again it acted the same ran rough and not as fast. Also change spark plugs but haven't put it back in the water to see if that was it. One of the spark plug looked fouled. Any hints on what I can check out to find the problem if it's not the spark plugs. It ran great all day long before this happened.