[Perry Timme]

I am working on the above motor for a friend. He has decided to sell the boat which has not been started in five years. The boat has approximately 20 hours on the motor. I drained all the fuel, cleaned the lines, changed the filters, and the owner ran all of the fuel out of the carbs before he put the boat up 5 years ago. Fresh fuel was put in the tank and the motor started right up. Unfortunately on the lake it possessed a rough idle and when you proceeded to give it throttle it would die. Hitting the electric choke would result in the boat motor taking off and running excellent at higher RPM's. However once you returned to idle and gave it throttle it would die. I was told Sea Form may help so I manually sprayed some down the carb and put the rest in the fuel tank. When I manually give it throttle the engine immediately tries to die without the motor in gear. I have ran 1-2 gallons of fresh fuel threw the engine with no improvement. The owner indicated the boat ran well at idle and high rpm five years ago. I have fooled around with the screws on top of both carbs but cannot tell I have made any difference. The spark plugs are new but may not be gapped properly. The owner put them in. I feel the problem is a fuel/air mix but perhaps not. Thanks for your help.

[smallfishcatcher]

I would put money on the carb being gummed up. I have had 5 different yamaha's a 70 2 stroke, a 115 stroke, 2 115 four stokes and a newly added 15 four stroke. I had the same issues you described with my 115 s stroke. Had the carb rebuilt and it ran like a champ afterwards. After sitting that long (even if he ran the fuel out) I bet the carb is gummed up. Just my opinion

[Ray Neudecker]

Seems an obvious fuel restriction. Remove the fuel disconnect and the engine mounted filter. Install a water seperator filter in line.
Replace the fuel pump and if needed redo the carbs.