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1985 Mercury 90 HP (Inline 6 CYL) Full Throttle no Power no Plane (Video Included)

D

Dboy95

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My dad brought us home a 16ft boat, we ran the engine on earmuffs on the driveway, sounded, and appeared to be running great. After a month or so of TLC and fixing up the interior on the boat we brought it out to the lake to use. To our disappointment the motor just doesn't want to plane, full throttle and we are still getting up and going. I'm adding a video so you can see and if anyone has input, experience, or knowledge to tell what could be the most possible issue here it will be greatly appreciated thanks in advance for helping. You may need to turn sound up/on. https://vimeo.com/340032908
 
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It was likely running on 3 or 4 cylinders.-----And they do sound great in the driveway like that.---------So post the results of a compression test.----Does it have spark on all 6 leads or just 3 of them.,-------If it has a plugged carburetor you can do serious damage to 2 cylinder !!-----Did you change the water pump impeller , yes or no ?
 
racerone said:
It was likely running on 3 or 4 cylinders.-----And they do sound great in the driveway like that.---------So post the results of a compression test.----Does it have spark on all 6 leads or just 3 of them.,-------If it has a plugged carburetor you can do serious damage to 2 cylinder !!-----Did you change the water pump impeller , yes or no ?
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Okay this week we will check compression, check for spark, should I take the carbs out of the engine? And water impeller seems to be running okay we have water coming from the hole.
 
A basic rule is to install a new impeller every 3 years o0n that motor.-----So might as well do that tomorrow.-----Or test the overheat warning horn on this motor if it has one !
 
racerone said:
A basic rule is to install a new impeller every 3 years o0n that motor.-----So might as well do that tomorrow.-----Or test the overheat warning horn on this motor if it has one !
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Okay I will add it to the list thanks for the input I’ll get back here with results on the compression test spark plugs etc, could be a few days but at least we know what we’re checking for thank you.
 
Update on the motor.

- Compression is the same on all cylinders and we are getting 150PSI
- Spark on all 6 leads
- All plugs are clean and working
- Water impeller pump put in working

Side note: Stator tested by removing positive from battery, engine stayed running

Next area to check?
 
??----Disconnecting the battery may not be a good idea on this motor.-------What voltage shows on the battery with motor stopped.----What voltage shows on battery at fast idle ?
 
racerone said:
??----Disconnecting the battery may not be a good idea on this motor.-------What voltage shows on the battery with motor stopped.----What voltage shows on battery at fast idle ?
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Brand new battery, running constantly 12 volt no drops in voltage. My old man said that's how to check the stator, anyways the compression and spark are all consistent where do you feel I should go next?
 
?----What voltage shows on the battery with motor stopped ---12.4 volts, yes or no ?-----Does battery show 13.5 volts or thereabouts with motor running , yes or no ?-----No need to disconnect the battery on an outboard motor to test a stator !!!!!
 
racerone said:
?----What voltage shows on the battery with motor stopped ---12.4 volts, yes or no ?-----Does battery show 13.5 volts or thereabouts with motor running , yes or no ?-----No need to disconnect the battery on an outboard motor to test a stator !!!!!
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Will check this tomorrow. In your opinion, could this be a stator issue by the way the motor is running in the video? Appreciated.
 
No its not a stator issue if you have good spark. You need to pull the carbs and do a thorough cleaning. Racer is right, you are running on half the cylinders. You will damage the dry ones, so fix it before you try running it any more. You fire that tower and your dog should end up in your lap, brother.

ps. DONT USE ETHANOL FUEL, PLEASE
 
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When you test voltage if it stays steady with no increase with RPM, your old mans advice just cost you a rectifier.
 
Pappy, that test is a bad idea for sure, but pa will cover the rectifier......probably, right Dboy? If you have a multimeter, next time just hook it to the battery and check for a voltage rise when motor is running. A fully charged battery is 12.65 volts. You should notice a charge voltage anything above this reading. Usually a little bitty charge at idle speeds.
 
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I'm having the same problem. I found a bare spot in the yellow stator wire close to the stator. The wire is corroded. I got a new stator in today. Will let you know if it solves my problem. Exhaust is clear, fuel pump rebuilt and removed the carbs. They are suprising clean. Float level and drop is close. However, 2 float springs are compressed 1mm out of spec. Mine is not a fuel issue either. Used a shop tank with fresh gas and was the same thing happening. All high speed jets were clear. Got kits to reseal the carbs as well. On purge cups this one sounds good (no engine miss). Starts good. For a 6 cylinder it should have more of a rumble out of the water. This one has been a challenge. I would much rather plug in my laptop on one and start diagnostics from there. I did learn their is an economizer hose running across the top of my carbs that should be plugged off. A fuel saving measure by Mercury that could lean the engine out too much at mid range. Yours may or may not have that. I'll let you know if my repair works after putting it on the water
 
Hey guys good news, replaced stator and rectifier and the boat is accelerating and planing, runs no problem now. I just want to thank everyone that helped us with the info it is greatly appreciated.
 
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