1988 20hp mariner dies at mid range throttle when warm

[mcurcio1989]

This motor ran perfect when I put it away for the winter. Took it out this year and it seemed to run perfect but after 10-15min at moderate to full power it started acting up. Once it starts doing this it will still idle in or out of gear perfectly. Out of gear it will rev up seemingly fine. Rev it up in gear and it will die (Its not missing or running rough its almost just like you turned it off.) However, if you give it a little power than go hard to wot it will work through and hold it usually but at about 75% of the normal power it has at wot. To restart it you have to give it a shot of gas and it will fire right up otherwise it just cranks. Normally it fires right up when shut off.

I have gone through the carb thoroughly twice now with a rebuild kit and replaced the gaskets. This is fresh gas and oil. The carb has been very clean every time I have gone through it.

It seems that 15 minutes is to long for it to be a mixture issue that develops when the engine is at operating temps it. After this time the engine has been up to temp for some time. Also the only screw I can adjust on the carb is an idle needle and it is idling fine. It seems likely that it is an electrical issue I'm just not sure what.

Also the fact that you have to give a shot of gas for it to fire up again is odd to me.

 

[oldman570]

Re: 1988 20hp mariner dies at mid range throttle when warm

If you have not replaced the fuel hoses with the newer ethanol restant fuel hose, then there is a good chance that this is causing the trouble. The older rubber fuel hose and rubber parts of the fuel pump and carb will deterate with the use of ethanol fuel. The inside of the hose can flake off and cut the flow of fuel to the motor most anywhere that fuel flows. Start at the fuel tank and replace ALL the hose, if you have not done so already. You might not have the carb set rich enough on the idle jet setting. Open that jet up a screwdriver bit width at a time and see if that is the problem. If that jet is set to lean at idle, the motor will starve for fuel when the RPM's are increased until the high speed jet takes over and provides more fuel. As you have found out there is no high speed adjustment for the carb. The only way to change the high speed fuel, is to change out the jet itself. This is not usually done unless the motor is being used at high elevations.
You should not rev a motor over a high idle (1800 RPM's) whe the motor is not in FWD gear, and in a test tank or on the water. Bad things can and do happen. JMO
Oldman570