2002 75hp mercury rough idle

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speckanator

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Aug 12, 2009
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I bought my boat/motor about four months ago and it had bad gas in it. Since that time I've run 4 tanks of gas and a can of seafoam through it. It ran 100% better after that, but still idles rough. I just had the carbs rebuilt and I can't tell the difference in how it idles or at slow speed. The mechanic says it's a 2+1 engine meaning at less than 1800 rpms it runs on 2 cylinders and the third one kicks in at 1800 rpms. He says the rough idle is normal and he checked everything, timing settings etc. It's a 2002 Mercury 75 hp 2 stroke. Once you throttle up it runs perfect, no hesitation, very smooth. Has anyone had this experience and if so is this normal?
 
milehighboater

milehighboater

Petty Officer 1st Class
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Jul 28, 2009
Messages
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Re: 2002 75hp mercury rough idle

I have a 99 75hp 3 cyl and all three are always firing. smooth as glass at idle. I think your mechanic may be going with the "it works though, doesn't it" doctorin. Does it ever die when it idles? If you prime the bulb does it remain firm/semi-firm? How is it out of the hole, does it stutter at all or does it go with the throttle? Does it run any better out of gear? Lastly, what does your tach say your idle rpm is, do you happen to know the WOT rpm?
 
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speckanator

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Re: 2002 75hp mercury rough idle

milehighboater said:
I have a 99 75hp 3 cyl and all three are always firing. smooth as glass at idle. I think your mechanic may be going with the "it works though, doesn't it" doctorin. Does it ever die when it idles? If you prime the bulb does it remain firm/semi-firm? How is it out of the hole, does it stutter at all or does it go with the throttle? Does it run any better out of gear? Lastly, what does your tach say your idle rpm is, do you happen to know the WOT rpm?
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Never dies when idling and the bulb holds firm. I never have to choke or squeeze the bulb unless two or more days pass before I crank it. No balking or stuttering when I throttle up. No better when out of gear. Idle does'nt register on tach. When I bump it up to about 1000 to 1200 it smooths out some. I don't know about the WOT.
Thanks for your response, I really apprciate it.
 
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fishdabayou

Cadet
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May 21, 2007
Messages
6
Re: 2002 75hp mercury rough idle

I have a 02 125hp, it is a 2+2 and yes it does idle a little rough, because only two cylinders are firing. It will even hesitate and stutter a bit just before the other two chime in at 2000 rpm. but it runs perfect after that. I keep plenty of sta-bil in mine all the time, just picked up a bottle of the green (ethanol blend) so will start using it this weekend.
 
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