HELP.. Mercury 850 (85 HP) Issues

chum1

Petty Officer 1st Class
Joined
Apr 15, 2010
Messages
359
Re: HELP.. Mercury 850 (85 HP) Issues

Hello Jimmy, My main problem was the switchbox after spending much time with the boat on the trailor in the water trying to link and sync i discovered no spark on two cylinders under load then verified by cdi troubleshooting guide. I tried to splice the hooked arm trigger wires but they were to far gone and while the flywheel was off i went ahead and changed the stater with a used cdi open air unit found on ebay. I think it came off a 50 horse.

switchbox p/n is 114-5772
trigger p/n is 134-6454 (hooked arm)
stator p/n is 174-5454k1

found these p/n's here:

http://www.marineengine.com/parts/c...ineengine.com/parts/cdi_electronics/index.htm

this stuff should be right here on iboats or roll the dice and check used on ebay or elsewhere.

i would check with the cdi troubleshooting guide first though it may save you some cash instead of throwing parts at it. rule out link and sync and fuel problems too
 

jimmy120

Petty Officer 3rd Class
Joined
Apr 27, 2011
Messages
80
Re: HELP.. Mercury 850 (85 HP) Issues

Hello Jimmy, My main problem was the switchbox after spending much time with the boat on the trailor in the water trying to link and sync i discovered no spark on two cylinders under load then verified by cdi troubleshooting guide. I tried to splice the hooked arm trigger wires but they were to far gone and while the flywheel was off i went ahead and changed the stater with a used cdi open air unit found on ebay. I think it came off a 50 horse.

switchbox p/n is 114-5772
trigger p/n is 134-6454 (hooked arm)
stator p/n is 174-5454k1

found these p/n's here:

http://www.marineengine.com/parts/c...ineengine.com/parts/cdi_electronics/index.htm

this stuff should be right here on iboats or roll the dice and check used on ebay or elsewhere.

i would check with the cdi troubleshooting guide first though it may save you some cash instead of throwing parts at it. rule out link and sync and fuel problems too

Thank you very much. Time to get to work. : )
 

jimmy120

Petty Officer 3rd Class
Joined
Apr 27, 2011
Messages
80
Re: HELP.. Mercury 850 (85 HP) Issues

Going to the mechanic today. Hopefully the problem will be resolved soon.
 

jimmy120

Petty Officer 3rd Class
Joined
Apr 27, 2011
Messages
80
Re: HELP.. Mercury 850 (85 HP) Issues

Stator it is. The mechanic told me the stator was only putting out like 10 to 15 volts at WOT. Mechanic said it should be putting out nearly 120 volts. He is going to replace it for $400 bones, ouch. Bring on another thousand. LOL. I only paid $800 for the boat, so I cannot complain. I just want her back to normal.
 

jimmy120

Petty Officer 3rd Class
Joined
Apr 27, 2011
Messages
80
Re: HELP.. Mercury 850 (85 HP) Issues

GRRRR! I spent $390.00 dollars and had that Stator replaced. I took it out today and its still doing the exact same thing. It will go about 1/2 to 3/4 throttle and wont go. It wont get up on plane. I am really upset after spending nearly $400.00 to fix the problem. The mechanic did, however, replace my choke solenoid for free (he had a used one laying around) and now the boat starts nearly instantly. Anyone else have any other suggestions. I noticed if I dropped the throttle from idle to full throttle, it killed the engine but wouldn't kill it (just bog down) if I gradually went to full throttle. Help me out....
 

Gomer50

Chief Petty Officer
Joined
Sep 5, 2009
Messages
507
Re: HELP.. Mercury 850 (85 HP) Issues

I am leaning more towards a fuel issue.These old Merc's love the fuel.I would say your on the too lean side or starving for fuel.I have a 74 850 with the older style carb but it took me 3 times rebuild the carbs and the proper link and sync before I got it right.Once dialed in right they will jump right out of the water.Test out your electrical componets before you go throwing parts at it.It can get very exspensive and come to find out it was something as small as a quality primer bulb (been there done that).Mine would bog down as yours is I went and invested in a 12$$$ american made primer bulb and problems vanished.Also switched to an inline fuel filter after the fuel pump not before.Another thing that was causing problems was my fuel quick disconnect on the motor was sucking air (just bypassed that).Just a bunch of little things to check..
 

jimmy120

Petty Officer 3rd Class
Joined
Apr 27, 2011
Messages
80
Re: HELP.. Mercury 850 (85 HP) Issues

I took my boat back out to the mechanic. He looked at it and determined the cause was the melted carburetor venturies. He replaced them with my spare set. It cost me $85.00 dollars. He said he tested it in a tank and the motor no longer dies out under load. I will test it once again tonight. Man these motors are touchy.

Is there anything I can do to prevent the venturies from melting again? They no longer make the part and I am not sure if I could find another set. Thanks. I will provide an update after my trip out to the lake tomorrow.
 
M

Maxz695

Guest
Re: HELP.. Mercury 850 (85 HP) Issues

beleive it or not I was running fine and then all of a sudden the damn motor bogged down and I couldn,t for the life of me get it to get back up on plane. I had some extra plugs in my tool box and changed them. The son of a **** took off like a raped ape.
 

jimmy120

Petty Officer 3rd Class
Joined
Apr 27, 2011
Messages
80
Re: HELP.. Mercury 850 (85 HP) Issues

beleive it or not I was running fine and then all of a sudden the damn motor bogged down and I couldn,t for the life of me get it to get back up on plane. I had some extra plugs in my tool box and changed them. The son of a **** took off like a raped ape.

LOL, a raped ape. LOL. I have put brand new plugs in it already.. : )
 

Wingedwheel

Lieutenant Junior Grade
Joined
Jun 16, 2009
Messages
1,071
Re: HELP.. Mercury 850 (85 HP) Issues

Jimmy it's too bad you're having all these problems. A few years back I bought a boat with a 1974 850 on it. I couldn't hear it run because the fuel lines were bad, but I checked compression and everything was great so I bought the boat. After fabbing my own fuel lines and rebuilding the carbs that motor started right up and gave me several years of great service before I sold the boat. I never had any problems with it and kinda miss it. Keep at it I'm sure that whatever your problem is, once you get it resolved you will have a great motor.
 

jimmy120

Petty Officer 3rd Class
Joined
Apr 27, 2011
Messages
80
Re: HELP.. Mercury 850 (85 HP) Issues

Jimmy it's too bad you're having all these problems. A few years back I bought a boat with a 1974 850 on it. I couldn't hear it run because the fuel lines were bad, but I checked compression and everything was great so I bought the boat. After fabbing my own fuel lines and rebuilding the carbs that motor started right up and gave me several years of great service before I sold the boat. I never had any problems with it and kinda miss it. Keep at it I'm sure that whatever your problem is, once you get it resolved you will have a great motor.

Thanks for the vote of confidence. Actually, replacing the venturies fixed the problem. I had it on the water yesterday and it ran great. I was even able to get my wife up on skis. :)
 

jimmy120

Petty Officer 3rd Class
Joined
Apr 27, 2011
Messages
80
Re: HELP.. Mercury 850 (85 HP) Issues

To all,
Thanks so much your help and input. Replacing my burnt venturies actually fixed the problem. Now, I hope it lasts.
 
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