Yamaha C85 2 stroke slows down at WOT when warm

[fatlaz]

This motor has 3 carbs and you mix the oil with the fuel. Before the season I changed all the jets, the float needles and seats and the idler needles as well as the fuel pump and the fuel filter and the spark plugs. I had water in my gas so it wouldn't start until I changed my gas. Then I had steering problems so I couldn't take it out until I fixed it. Now after pulling about 200 lbs on the tube for about 20 minutes my motor revs down to about 30% full throttle. If I put it in neutral, it will die, but if I let it sit for about a minute it will start right up and run correctly for about a minute of two. The pee hole is circulating water fine. There is no overheating alarm, though I've never heard one on this motor, so I don't know if it works. Any guesses?

 

[fatlaz]

BTW this is a 1995 model year motor

 

[Jim311]

Have you looked in the carb throats to see whats happening when it does this? I suspect you adjusted your carb floats improperly and under high throttle/load the bowls aren't filling all the way up with enough gas. Probably runs great any other time but after running hard the carbs are taking more fuel than the bowls are providing.

 

[fatlaz]

The carb floats are all plastic. I don't remember any adjustment. In fact, when I put the replacement float and pins that the float pivots on in, the float was rigid and would not move when I tightened the screw that held the pin in. So I put the original floats back in. But what you are describing sounds logical.

 

[Jim311]

I think its those little metal clips that hold the float valve on that you adjust. Also you have to make sure the rubber/plastic cap that you put onto the float valve needle is pushed all the way in or it won't open/close properly. There are measurements in a factory service manual that show what position the float should start to open the valve at relative to the body of the carburetor.

 

[fatlaz]

I'll check it. Thanks!

 

[fatlaz]

Here's what was wrong: I didn't have my contacts in or glasses when I mixed the oil with the gas. My tank holds 30 gallons...I just filled it up...and I only put 1/3 of the oil that was supposed to go in the gas...I couldn't read the mix ratio on the side of the bottle...so my motor overheated and the overheat protection reduced the rpms. I added the correct amount of oil and ran it for 20 minutes yesterday and everything seems fine.