2 stroke 40 hp yamaha

[tader]

hey guys i have a precision blend 1987 40hp 2 stroke yamaha. the problem is the boat will only run for about 30 seconds boggs down and dies. I assumed it was the carburetors so i rebuilt them and had the same results. I then replaced the fuel pump ( not sure it is really a fuel pump because it has no motor in it but does contain diaphragms and it is where the gas travels after leaving the fuel filter.) the boat will still run for about thirty seconds and then dies. so i cleaned the carburetors again to make sure they were free of trash. I then replaced the fuel line and bubble and this did not fix the problem. the boat has fresh clean gas and the spark plugs look fine. i took the air box off the front of motor and can see the jets in the carburetors spraying fuel while the motor is running. i do not believe that it is a fuel issue anymore as i can see the fuel being sprayed into the carburetors. I am stumped and any direction to what it may be or if you had the same problem and found the fix would be greatly appreciated.

thanks

tader

[Cray]

Taxer this is not much help but I have a 88 40 HP mariner that has a 2cyl Yamaha power head. Mine started not starting then if I got it running it might run fine for a while then run but have no power like running on 1 cylinder. Finally got to where it was impossible to start. Did all the things you did several times and never could get it fixed. Have determined it has to be something in the stator or coil. Had it to 3 shops and no one knows what to do with it. I'm thinking you could have a electrical problem of some kind. Mine has a single coil that fires both cyl. Check all your wiring for something loose or rubbed bare.

[MDCrappie]

When it dies, do you try and restart it? If so what happens? Does it start back up and run for 30sec again? Is it hard to start? or does it not start at all for a period of time?
When it dies, is the ball soft?
Any difference warm or cold?
Are you throttling it up? and it then dies?

Lost of answers needed to diagnosis properly.
Yes that is a fuel pump, is is vacuum driven, not electrical

Doesn't sound like carb running out of fuel if it only runs 30 secs.

Maybe time it and see how long is actually runs.

[Scrapper]

First and formost go to iboats.com or comparable and get a manual. Willl save you LOTS of money in the long run. You say the plugs look fine. But have you tested spark?? You can get a single spark tester at the parts house for cheap. It takes longer than the multiple testers because you have to do one at a time. See what the spark looks like.....and note the color. Should be bright and strong; white to bluish white....not yellow. I would also trace all my wires paying special attention to the kill switch. Many times this get a loose contact...they are spring loaded...it will run for a bit then die. As already stated trace everything and check close for corrosion. I agree with the above though it is probably electrical. But those are the hardest to find. If you get a manual go through the coil, stator, powerpack, voltage regulator tests.

[JayLT76]

I had a simular problem with my mercury, turns out it was my choke solenoid. Easy to test, remove the cowling without starting the motor push in the choke. You should hear a click sound as you push in and then release. If you dont hear this "click" good chance it is getting stuck and killing the motor. I did the same as you, i rebuilt my carbs and fuel pump changed fuel lines then found out all along it was the choke solenoid. It's and easy thing to check and not too expensive to replace if that is your problem. Hope this helps, good luck.