'85 50HP 2-Stroke - Does not run in water

[joewg3]

Hi All - I have an '85 Mercury 50HP 2-stroke on my '16' Alumacraft. The motor runs fine when not in the water. I hooked up the ear muffs and ran it for about 5 minutes. No overheating, revving great, idles super smooth, etc. When I put the boat in the water, I go about 20 yards and then it bogs and seems to overheat. I did order a new impeller which should arrive tomorrow.

I took the advice of those on the forum and just pulled the carbs, cleaned them, new plugs, new fuel lines, new fuel filter. I did not make any adjustments to the carbs. I will note that the fuel filter, when not running, is about 1/4 full whereas before it seemed like there was more fuel that stayed in it. My friend thinks that it may be a fuel issue. At this point I'm about ready to use the motor for an anchor.

Any help would be incredibly appreciated.

 

[Chris1956]

Richen the carb idle mixtures 1/8 turn and try it in the water. Repeat if necessary.

 

[racerone]

They all run nice on a hose.----Might be running on 3 of 4 cylinders or 2 of 3 cylinders.----Does spark jump a gap of 3/8" on all leads , yes or no?-----Test run with another tank and hose.

 

[joewg3]

They all run nice on a hose.----Might be running on 3 of 4 cylinders or 2 of 3 cylinders.----Does

 

[joewg3]

I'll check the spark asap. Would a fuel issue cause it to overheat? Sorry, I'm new to outboards! Whole different beast!

 

[joewg3]

Richen the carb idle mixtures 1/8 turn and try it in the water. Repeat if necessary.

Looks like the top 2 cylinders are running REALLY lean. Left to right is top cylinder to bottom.

 

[racerone]

If you do not know the age / condition of the impeller you should install a new one.

 

[joewg3]

If you do not know the age / condition of the impeller you should install a new one.

I've got a new impeller coming tomorrow. I probably should have changed that right off the bat. Looks like I definitely need a carb adjustment though. Top 2 cylinders are wicked lean.

 

[racerone]

When lower unit is off check exhaust tuner for blockage.

 

[Chris1956]

None of the spark plugs are running really lean, IMO. The bottom ones are indeed wetter though. Really lean is a green or white tint to the spark plugs.


You might check/rebuild your fuel pump, as the lower cylinder crankcases normally power the fuel pump, and if the diaphragm leaks, it will flood the bottom cylinders.