Reed Valve or carb problems on 650 yamaha jet ski?

Question

How can I tell if my reed valves are bad on a 1991 650 yamaha jet ski? I took them out and the flaps were closed. The ski runs but after less than 5 mins. it acts like it is running out of fuel. If it is not the reed valve it must be the carb. Any help would be great thanks Bill.

Answer 1

Even if you removed the reed valves it would still run. As long as the reeds close and are not cracked they should be fine.

You may have a carb problem and it's time to rebuild it or it could be elsewhere in the fuel system. Check your filter/water trap. If you get water in there it will restrict fuel flow. Also check your tank vent. If plugged it will run a few minutes and then run out of fuel. Check for water in your tank.

Check for exhaust leaks. They will fill the compartment with fumes and rob your engine of air and the motor will die out after a few minutes of riding. A plugged air intake will do the same.

Other things to look at if all else fails. Being it's a 2 stroke if there are bad crank seals it will draw in air when warm and lean out the motor. Unburned oil will also leak out and leave a big mess in your stator cover or by your drive shaft output.

Answer 2

How many hours do you have on your engine?  Stock yamaha reeds are pretty tough, should have to be replaced for at least 300 hours.  Usually they'll start to chip when they go bad.  You could have a carb problem, but you also should check your gas filter and electrical system to rule out those possiblilities.