1999 Yahama 70 Issues

[Stephen.Ryan]

New to the board and I know its probably been asked a million times but here it goes.

I have an old 1999 Yamaha 70 outboard. The old owner that had it before me let it sit for about 10 years with out running. I cleaned everything and got it to start. Water tested it and it would not rev up underload. Took it back home and fully took the carbs apart and bought rebuild kits and cleaned the carbs again. Changed the spark plugs and of course when putting the oil tank back on broke the fuel filter so replaced that. I also replaced all the fuel lines. The motor runs a lot better now. Now the issue that I have, is every time I put the boat in the water in the morning it starts and runs and idles fine but wont go over 2k rpm. So I run it like that for about 10 minutes and then I turn the motor off and fish for about 15 to 20 minutes and then try the motor again and she runs perfect for the rest of the day. Then the next day the same thing happens the first 10 minutes wont run so I wait and then runs fine. Does any one have any suggestions for me. Thanks in advance.

[99yam40]

do you have gauges to indicate if you have a low oil level indication?
does the alarm system work(sound a buzzer) if a low oil level is seen or an over heat?

Those motors limit RPM if those conditions happen, along with buzzer and lights if you have them
you may not have low oil or overheat but the sensors or wiring says it is.

can you tell if all plugs are sparking when this happens?
A timing light or spark tester should indicate spark when hooked to the individual plug wires.

leaking fuel pump will dump too much fuel into #3 crankcase

does this have a choke or prime start system to help with cold starts?

[Stephen.Ryan]

There is a light that is supposed to come on when over heat and low oil but it has not done either. There is almost a full oil tank.
As far as the plugs I have not been able to check that yet.
It could be a leaking fuel pump I am checking that this week. I think there may be an air leak in the system somewhere. I recently took it out and noticed that when I primed it I saw air coming back into the fuel filter. I don't know if that is part of the issue but I do know that is not supposed to happen.

The motor starts up fine and idles fine with the cold starts. Its just underload I am having issue but like I said after about 10-15 min of idling and then turning it off for 10-15 min she runs fine all day.

[99yam40]

test the alarm system to make sure it is functioning properly.
just because it has not come in does not mean it works