attention motorheads

[flyboyo2]

'89 Mariner 75 has been running great.  Last Wednesday at 4200 rpm she was clocking 28 mph, not bad for a 28 year old motor.  Today couldn't get over 3000 rpm and 15 mph and the motor was surging. After 20 minutes of running I was virtually out of gas. My anchor began to drag and she wouldn't restart.  As I was drifting past a new Tiara, with a apprehensive crew on board I might add, the owner threw me a line to arrest my rampage through the anchorage at the Tyndall AFB airshow.  I had used about 10 to 15 gals of fuel in 20 minutes so the fuel must be going overboard. No gas in the bilge and I can't see where it's leaking in the engine.

Where do I start? Don't even mention a new motor, the Admiral has vetoed that solution.

[GoneFission]

Hard to tell, but it could be the starter valve choke is stuck in the on position. 

[flyboyo2]

I was attemping to see if I could pin down an external carb or fuel pump leak and as I pressed the primer bulb fuel came out the exhaust.   I hope I don't now have a 250 lb anchor on the back of the boat.  Do carbs and fuel pumps leak through to the cylinder and out an open exhaust valve? If so what could be the culprit?

[GoneFission]

You could also have a stuck carburetor float.  Pull the spark plugs and see if one or several might be very wet.  Carbs on that motor are simple and easy to rebuild/overhaul.  Here is a video for a setup similar to yours:
https://www.youtube.com/watch?v=OBEzWLBAtjU 

BTW - your 2-stroke motor does not have exhaust valves - it uses ports:   
https://www.youtube.com/watch?v=LuCUmQ9FxMU 

Good luck!   

[flyboyo2]

# 3 plug was very wet, the local Mercury experten said he thought the fuel pump diaphram was bad.  If so, excess fuel goes into the crank case. Rebuilding the pump now. I have a sneaking suspicion that you are right and it's a carb float.

[flyboyo2]

Leaking fuel problem was the fuel pump, it had a tear in one of the diaphrams and was pumping fuel into the crankcase.

Now the idle rpm is 1500. Is there a method of reducing the rpm without going through thr goat rope of changing the timing?

[GoneFission]

Idle needs to be set with the engine in gear to get the right result.  There should be an idle stop screw with a lock nut.  With the engine warm and in gear, loosen the lock nut and adjust the idle to about 750-800 RPM.  Tighten the lock nut back down and you should be good to go if the idle stays put.  Sometimes tightening the lock nut will change the idle speed, so you may have to do this a time or two to get it right.     

[flyboyo2]

Thanks for the info. I was over thinking the proceedure after I read the repair manual.