75hp Mercury issues on maiden voyage...

[leeklm]

Hello all,

Picked up a "bargain" (i think) boat to take my 13yr old fishing... 1985 or 86 Mercury 75hp/ 2-carbs.

Motor starts up easy, but will not idle well until warmed up. After warm, it generally runs good except...

-- on ocassion, the motor will bog down & want to die when accelerating past 1/2 way or so. This condition tends to clear up after reving it in neutrel, and then runs fine and pulls well under full throttle. This happened in my driveway and on the lake.

--engine wants to also die when trying to run it at trolling speed. give it just a little more gas (1/4 throttle) and runs fine.

I am a backyard mechanic, but limited experience with outboards. Will a Service Manual provide specs and troubleshooting with linkage controls, etc??

Thanks for your help & suggestions!!

 

[ohio river rat in KY]

Re: 75hp Mercury issues on maiden voyage...

good luck man, were in the same boat.....i got a deal too but mine was a 80hp mariner. mine i think was the carb ajustment, plugs,fuel line, had a coil pack not grounded out good (found that with carb cleaner) not good,cleaned the carbs 3 times,and checked the timing. even took it to a shop to have worked on and this was all after i got it back.. check all of this and you might have some luck or look at some of my old post a lot of good info on them what people has told me and it all helped out... i hope i got mine going good now just got to hit the water good luck

 

[Wingedwheel]

Re: 75hp Mercury issues on maiden voyage...

If you don't know the history of this engine, I would really suggest rebuilding the carbs. Thats not too expensive and it can't hurt.

 

[nzahradka]

Re: 75hp Mercury issues on maiden voyage...

I have had similar issues with my 1986 75 hp Mercury, and for me, rebuilding the fuel pump as a first step solved most of my idle issues. Replacing the diaphragm is a very simple procedure that takes just few minutes and the kit is cheap. I am now at the point where I am going to pull the carburetors and give them a good cleaning, but if its running like you say, I would start with the fuel pump.

Also, if you're not doing this already, I've also found that this motor runs much better on 93 octane. It doesn't really affect idle, but the motor knocked really badly on the lower octane fuels. And from what everyone I've talked to tells me, it will always be ornery until it warms up. I'm told that's part of the fun of owning a Mercury.

And yes, get a manual. The Clymer manual for this motor covers a lot of engines (45-225 hp and from 1972-1989) so you have to search a little for the specifics on this engine, but it is invaluable. I'm not sure if the Seloc manuals for the Merc 75 are any better.

Good luck - I've had mine for about 10 years now on a 18' Aquasport with no regrets on buying it.

 

[latin monkey]

Re: 75hp Mercury issues on maiden voyage...

a factory service manual would be the best way to go

 

[leeklm]

Re: 75hp Mercury issues on maiden voyage...

Thank you for the advice. I see that the 75hp 4 cyl was only built from 84-86? I ran the heavy dose of seafoam in the driveway just for kicks, and made another run tonight on the local mud hole. Motor was running decent. It will idle no problem in neutral, but then dies after 30 seconds or so running at trolling speed. Motor ran very well at WOT for the 15 minute run I made.

The manual sounds like a good place to start!

 

[flyinbryan]

Re: 75hp Mercury issues on maiden voyage...

this is actually my first post here, but ive been lurking for a while. great site.

the reason i chose your thread to post my first thing here is because my 50hp merc did the exact same thing yours is doing.

im not a mechanic by trade, but being a tradesman (electrical contractor) i figured i would be comfortable trying to troubleshoot mine, so i bought a sevice manual.

best boating investment i ever made.

the carbs on these ole mercs are so simple,,,its actually enjoyable to rebuild them.

i now rebuild them every year just for the heck of it, and have yet to used a single new gasket, or part of any kind. just a quick detail strip, and a good soak in the chem-dip, them hot soapy water and a good cold water rinse, and it purs like a kitten.

highly suggest you pickup a service manual.

 

[nzahradka]

Re: 75hp Mercury issues on maiden voyage...

Thanks, flyinbryan, for your post. I read all the multitudes of opinions on carb cleaning options that you can find on this forum, and I was happy to see the basic chem-dip is a safe way to go for these particular carbs. The Clymer manual doesn't say yea or nay to dips, just says follow the instructions on the carb cleaner. Probably why I should invest in a factory manual...

 

[leeklm]

Re: 75hp Mercury issues on maiden voyage...

As recommended, I bought a Seloc manual, rebuilt the carbs and replaced the diaphram (funny how the chem-dip cost more than all of the parts...)

Motor is definitely running better. The only thing that keeps it from running "perfect" is a slight hesitation at mid-throttle when accelerating slowly. Almost feels like the delay when the secondary opens up on a quadrajet... The motor runs at idle/trolling speed with no problem now, but did tend to "load up" a little under acel after trolling a while. However, it would clear up pretty quickly and ran great at full throttle. The motor ran very well when going from idle speed to full throttle (like pulling a skier).

I still have a heavy concentrate of seamfoam in this batch of fuel. I am not going to worry too much until I run a clean batch of 92 oct non-alcohol fuel and see how it does. If no improvement, I am still pretty happy with how it is running.

Thanks for the advice!