90hp 3 cyl rough idle,missing on throttle up

ecs17a

Cadet
Joined
Nov 7, 2010
Messages
18
Hello all,
This is my first post so I have to thank every one out there before i start.I have a 1992 3 cylinder 2 stroke Mercury that does not want to rev up very smooth.Starts on first crank.Seems to idle ok but when I lift the fast idle arm it misses badly.Rum,Rum,Rum.Mabey a quarter to a half second intervals.When idle lowered it backfires once or twice with the blue grey cloud.I have spark on all wires but the bottom coil wire shocks me when Its pulled out.cylinders are all getting fuel as the plugs are somewhat wet when pulled.This motor has not run in about 3 years but ran very strong last time out.

Thanks
 
Last edited:

jerryjerry05

Supreme Mariner
Joined
May 7, 2008
Messages
18,031
Re: 90hp 3 cyl rough idle,missing on throttle up

Do a compression test.If that's ok then look into the fuel system.Ethanol is messing with lots of motors.
Fuel pump diaphram,replace it.Any hoses soft or mushy.Check any filters and clean the carbs.
Replace the squeezie and check tank for water.J
 

Faztbullet

Supreme Mariner
Joined
Mar 2, 2008
Messages
15,884
Re: 90hp 3 cyl rough idle,missing on throttle up

This is a no brainer, if engine has set that long(3 yrs) it needs carbs and fuel system repaired. Ethanol along with the mixing of fuel/oil form gum in the carb due to fuel evaporates and leaves oil residue behind. The ethanol can also leave a crystal looking residue as it affects aluminum we techs call "ethanol salt".. If the EPA allows the new E15 on the market we are all screwed as it will be sold as "regular" gas and E10 blend as "premium"....

http://www.saltwatersportsman.com/article/News/NMMA-denounces-EPA-partial-approval-for-E15-ethanol
 

ecs17a

Cadet
Joined
Nov 7, 2010
Messages
18
Re: 90hp 3 cyl rough idle,missing on throttle up

This is a no brainer, if engine has set that long(3 yrs) it needs carbs and fuel system repaired. Ethanol along with the mixing of fuel/oil form gum in the carb due to fuel evaporates and leaves oil residue behind. The ethanol can also leave a crystal looking residue as it affects aluminum we techs call "ethanol salt".. If the EPA allows the new E15 on the market we are all screwed as it will be sold as "regular" gas and E10 blend as "premium"....

http://www.saltwatersportsman.com/article/News/NMMA-denounces-EPA-partial-approval-for-E15-ethanol

Thanks Faztbullet,
I figured this might be the case after reading all of the other posts regarding this issue.Im still concerned about the spark being sporatic and weak.What should this arc look like when I pull the wire and hold it to the block?Also,On a scale of 1 to 10 how difficult would a carb overhaul be?

Thanks
 

ecs17a

Cadet
Joined
Nov 7, 2010
Messages
18
Re: 90hp 3 cyl rough idle,missing on throttle up

This is a no brainer, if engine has set that long(3 yrs) it needs carbs and fuel system repaired. Ethanol along with the mixing of fuel/oil form gum in the carb due to fuel evaporates and leaves oil residue behind. The ethanol can also leave a crystal looking residue as it affects aluminum we techs call "ethanol salt".. If the EPA allows the new E15 on the market we are all screwed as it will be sold as "regular" gas and E10 blend as "premium"....

http://www.saltwatersportsman.com/article/News/NMMA-denounces-EPA-partial-approval-for-E15-ethanol

Thanks,
This was the problem.Had the carbs re built now it screams!
 

ecs17a

Cadet
Joined
Nov 7, 2010
Messages
18
Re: 90hp 3 cyl rough idle,missing on throttle up

Do a compression test.If that's ok then look into the fuel system.Ethanol is messing with lots of motors.
Fuel pump diaphram,replace it.Any hoses soft or mushy.Check any filters and clean the carbs.
Replace the squeezie and check tank for water.J

compression was great 161,159,158.Carbs were gummed from sitting.No brainer like Faztbullet said.My mechanic removed them,cleaned and installed in 2hr.Very strong running motor now.

Thanks for your help
 
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