1999 25mshw..motor cutting out at full throttle

[marlon123]

but runs fine up to about 80%..seems like a simple adjustment..right?

[marlon123]

I got it back running..just a little fuel delivery issue

thanks for all the help

[99yam40]

Check compression and spark on all cylinders, could be bad plug or wire.
if all is good.
Check fuel pump for hole in diaphragm and then pull and clean carbs. There is no adjustment for high speed jets

[Top Thomas]

Marlon.

I have twin 25's on my boat and I have had the same problem recently with both motors and now one is blown, and the other is a bit down on compression. One motor would cut out at full speed after about a minute then would not start for about 10. This happened on both motors in the space of a month. I stripped the carbs, replaced fuel lines, new fuel, and just about everything else.

I eventually took the motors into a mechanic and compression was way down on the one (35 and 85psi) . The mechanic said the motor has overheated due to incorrect oil mix or no oil at all. I am pedantic when it comes to mixing my fuel before I put the tank back in the boat, so I suggested sticky thermostats to him and he agreed that this could be a possible cause.

When I took the thermostats out they had quite a bit of corrosion/lime scale on them. The thermostat is closed when the motor is cold to allow the motor to heat up quicker. If the thermostat sticks (doesn't open), the cooling water doesn't circulate around the whole motor. The same as a thermostat in a car motor.

Basically root cause will be not flushing the motor long enough for it to heat up and the thermostat to open after using it in salt water

As 99Yam40 suggested, check compression then I would change the thermostat to eliminate a possible cause.

I could be totally wrong on this one but please keep us updated on your progress so I can put my mind to rest.

Hope this helps

[marlon123]

My problem was a lot less complicated

Thomas, thanks for the help..

but my problem was a lot simpler and is fixed..it was a bad fitting connecting the fuel line to the engine....5 bucks at Walmart did the trick

BTW..I rebuilt the the power unit on this motor last summer (replaced pretty much everything but the block) for less than 400 bucks...with the service manual, it was a really easy job, and the motor runs better than the day I bought it new..

My advice for this 25hp motor is to change your water pump every spring..those cheap little things will fly apart with no warning, and you can warp things in no time flat

[Top Thomas]

Marlon.

Good to hear you found the problem. Please can you PM me any details you have on the rebuild, parts ect. I am keen to give it a go myself. Did you have to get a reboar?

Thanks

Thomas