Merc 85HP 850 starts but dies when key is release off start...

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cyberpitz

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Oct 13, 2011
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I believe it is a 77 model 85HP 850. I just bought the boat from a friend. The orginal problem was that when the boat was in the water it would die when you put it in gear (forward only). Reverse would not kill the engine. On muffs it would not die if put into forward gear. Compression ran 110 or just right at on all cylinders. Idle was alittle rough, slight miss. Took the boat to a shop that was recommended by a few people that I work with and now I have more problems than I started with. The shop was running test on the motor and I was told " disconnected number 1 sparkplug wire while running to determine slight miss. Engine died. replaced sparkplug wire engine would not stay running when key was released off of the start position. Replaced ignition switch. No luck. Wiring harness is in good shape no shorts, looks like the wires according to the color code charts are correct. Starter does stay engaged when the engine is running now. I have even started engine unplug harness at engine and still dies. I am a newbie at boats and have tried everything that I know to do at this point. Need help..Thanks.

Did go pick the boat up from the shop that caused more harm than good before anything else could be messed up.
 
fisherman81654

fisherman81654

Petty Officer 2nd Class
Joined
Sep 5, 2011
Messages
135
Re: Merc 85HP 850 starts but dies when key is release off start...

cyberpitz said:
I believe it is a 77 model 85HP 850. I just bought the boat from a friend. The orginal problem was that when the boat was in the water it would die when you put it in gear (forward only). Reverse would not kill the engine. On muffs it would not die if put into forward gear. Compression ran 110 or just right at on all cylinders. Idle was alittle rough, slight miss. Took the boat to a shop that was recommended by a few people that I work with and now I have more problems than I started with. The shop was running test on the motor and I was told " disconnected number 1 sparkplug wire while running to determine slight miss. Engine died. replaced sparkplug wire engine would not stay running when key was released off of the start position. Replaced ignition switch. No luck. Wiring harness is in good shape no shorts, looks like the wires according to the color code charts are correct. Starter does stay engaged when the engine is running now. I have even started engine unplug harness at engine and still dies. I am a newbie at boats and have tried everything that I know to do at this point. Need help..Thanks.

Did go pick the boat up from the shop that caused more harm than good before anything else could be messed up.
Click to expand...

As many would say on this site,first make sure you have fire to all cylinders,second fuel to all carbs and third you have already done, a compression check on all cylinders.

See if you can locate the serial number,it will help you get more replies.

http://www.marineparts.com/partspages/techhelp/tech1.htm

This may help you also after you find out the correct year for sure.http://www.crowleymarine.com/parts.cfm
Thats why we need a serial number.
Just a guess, but it could be a bad solenoid.untitled2.jpg
That could be the problem as to why it cuts off when you release the key.
With the key on the on position,check the side off the solenoid that feeds the motor ,not the battery side,or then again check both sides.if one side does not have twelve volts,providing you have a good ground,then the solenoid is bad.
 
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CharlieB

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Apr 10, 2007
Messages
5,617
Re: Merc 85HP 850 starts but dies when key is release off start...

You may now have two separate problems.

First, dying when shifting into forward gear but not into reverse may be a sign that the idle circuit of the carbs are beginning to get dirty and not pass enough fuel for the increasing load.

Second, looses spark when releasing the key from cranking. Is this a distributor motor? If so, this may be an indication of a failing trigger. Pulling plug wires on a running motor is often done to troubleshoot, but should never be done without grounding the wire to give the electricity some place to go, as it will take the path of least resistance, shorting to ground somewhere, possibly damaging something, like arcing inside a distributor cap creating a carbon path that can cause future problems.
 
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cyberpitz

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Oct 13, 2011
Messages
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Re: Merc 85HP 850 starts but dies when key is release off start...

Ok I have an update to my post. The serial # is 3874155 which makes this motor a 74 model 85HP 850.

I have checked the solenoid and everything seems to be fine with it.

(Is this a distributor motor? ) Yes this is distributor motor.

I hope this information helps anyone help me with my motor. Thanks
 
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CharlieB

Vice Admiral
Joined
Apr 10, 2007
Messages
5,617
Re: Merc 85HP 850 starts but dies when key is release off start...

CDIElectronics has an excellent Ignition Troubleshooting Guide available for free download on their Support page. Get it and study the section on your ignition, you should find on the distributor ignitions a section that deals with your exact symptoms, sparks during cranking then failing as soon as you release the key. They will spell out how to test the trigger to PROVE if it is failing.

Meanwhile, adjust the idle mixture needles out almost 1/8 turn from where they are now set to provide a bit more idle fuel until you take the carbs apart for proper cleaning.
 
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