Force Mercury 50hp runs only at wot

gsp135

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Aug 10, 2003
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Working on a 1996 50 hp 2cyl Mercury Force. It will start and run only at wide open throttle. It had no problems when last used and shut off, but next day this is what it did. 105 and 110 cylinder compression. Had the carb off and cleaned out. Trigger coil has been replaced but seems to have been good. Don't know if related but noticed the tach is not working. Any thought are appreciated.
 

jrlogan11

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Apr 7, 2003
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67
Re: Force Mercury 50hp runs only at wot

Let's get some more info. I assume you are starting in neutral with the throttle all the way forward (which is not really wot, by the way. wot in neutral would trash your engine). When you start it like this it runs fine? Then what happens? When you pull back and put it in gear, it dies immediately, or are you able to get it in gear and running? Does it sputter at all like it's losing fuel, or does it just die. Need some more clues! :cool:
 

The Marine Doctor

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Jul 25, 2003
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2,177
Re: Force Mercury 50hp runs only at wot

Check for voltage on the low side "Blue wires" on the stator.<br /><br />TMD
 

gsp135

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Re: Force Mercury 50hp runs only at wot

It will start in neutral at full throttle. can't say that it runs fine there, I won't leave it at that speed. I immediatly back off when it starts. It dies when the trottle backs off to three-quarters, about the point where the throttle plate closes but the trigger coil is still advanced. My first thought was the low speed circuit of the carb but I've sprayed carb cleaner and air through the ports. They are all open.<br /><br />What should the voltage at the blue wires be?
 

turtle1173

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Nov 29, 2001
Messages
437
Re: Force Mercury 50hp runs only at wot

Are you able to shift it into gear? Did you let the carb sit in cleaner or did you just spray through the passages?<br /><br />Shane
 

gsp135

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Re: Force Mercury 50hp runs only at wot

The engine dies when I bring the throttle back in neutral. I can't get far enough with it to get it into gear running. The carb has soaked.<br /><br />Marine Doc: I can't leave the engine running long enough to measure the voltage. There are no blue wires, just 2 yellows, a green/white, and a white/green. The resistance between the grn/wht and wht/grn is 160 ohms; both open to ground. About 1/2 ohm between the yellows.
 

The Marine Doctor

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Jul 25, 2003
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2,177
Re: Force Mercury 50hp runs only at wot

The green wires are for the voltage for the stator. The stator runs in series. To measure the voltage...hook a + to white/green - to the Green...and check for voltage.<br /><br />Its hard to say if you will find voltage though..as you need a DVA meter...but check anyway.<br /><br />This is a high enery stator...so it does not have a low or a high speed...its all in one.<br /><br />Unfortunately this is a hard ign to diagnose unless you have the right tools. :( <br /><br />Check for a damp plug...this will tell you if there is an ign problem.<br /><br />TMD<br /><br />TMD
 

gsp135

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Aug 10, 2003
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Re: Force Mercury 50hp runs only at wot

Pulled the plugs. They were wet. Figured that was because of choking the engine and not running long enough to get hot. They are wet with black fuel which bothers me. Another observation is that the bottom of the engine housing was full of small pieces of the foam rubber that was on the engine cover for sound deadening. What's the likelyhood that some pieces went through the carb and reed valves and is sitting in the crankcase and exhaust. The engine hasn't run 30 seconds in total time but the water in the tank is topped with a really black sticky tar like oil. Is there suppose to be a filter or screen over the carb inlet?
 
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