Mercury 75HP unwilling to go to high gear

ToStev

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May 24, 2003
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5
My grandfather has just recently passed away, and I have inhieratied his Mercury 75HP. I know the boat year from the registration (Mitchell 1973).<br />What I do not know is the engine year. My father tells me my Grandfather bought it about 2 years before his stroke (which was in 1996)(I do not think it is new.) It is a 4 cycle <br />I found this pic while browsing ebay. It is a book for mercury's. It is from 1972-1989. a broad rang for me to search. <br />
merc.jpg
<br />Well that engine on the front is the spiting image of my grandpa's. It sat in is front yard from 1998 till about 2 months ago, when I took it to my house. It would not fire up. It would turn over and run for 3 or 4 secs then give out. I every night for 1 week kept trying to run it. Then 1 week later I got it to run (only at full throttle) in an idle.<br />Seeing my opportunity, I bought some carb cleaner. and let it run as that for 10 - 20 min. I unhooked the gas let the gas that was in the carb run out then hooked the gas back up. It never ran sweeter. Or so I thought.<br />When I got it in water and in gear it will not idle. It wants to die and I have to give it a little more gas. It will not want to go into high gear either. Well let me correct that. Once I max out the low gear I can get it to go into high gear but only if I increase the throttle about 1/8 of a inch every 10 secs. Each time an increase the engine wants to die out but recovers and goes on. Then takes about 20 secs to get to plane. So...<br /><br />Does anyone know what is going on? <br /><br />PS: I talked to a guy at work (not all that smart in the ways of outboard Mercs but more then me) and he said if it sat their for that many years it could be the vac line. Something about it have cracks or maybe even bad connections.
 

roscoe

Supreme Mariner
Joined
Oct 30, 2002
Messages
21,819
Re: Mercury 75HP unwilling to go to high gear

#1- post the model number and serial number, so people can give you specific information.<br />#2- get a shop manual like the one you have in the picture. You can order a new one here, click icon at bottom of this page.<br /><br />Problem seems to be fuel related, either the fuel pump or carbs need to be rebuilt. Should probably do both. Also check the compression on all cylinders, you don't want to be sticking money into a motor that needs a rebuild, unless you know in advance. Does the fuel primer bulb get firm when you pump it? Does it go flat when running? If so, does engine run better when you pump it while running? Also check for spark to each cylinder and replace plugs if you haven't yet.
 

ToStev

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Joined
May 24, 2003
Messages
5
Re: Mercury 75HP unwilling to go to high gear

I have not replaced plugs.<br />The bulb is and allways stays (unless I do nothing for 3 or 4 days) hard.<br />I am a newbie here so is thier somewhere I can be shown how to check the compression on all cylinders.<br />I have pulled off 1 plug at a time to see if it would run with out it. Each time it would start up then 2 secs later die. This happened on all 4 plugs.<br />Sorry I do not know the model or serial number as the boat itself is at anouther location from me. About 150 miles south of me. I will be down to check it this week.
 

ToStev

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May 24, 2003
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Re: Mercury 75HP unwilling to go to high gear

go and swing
 
Last edited:

Hooty

Rear Admiral
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Oct 2, 2001
Messages
4,496
Re: Mercury 75HP unwilling to go to high gear

That's a 1984, ToStev and the wires are probably rotten. If they are, you can probably buy the whole wiring harness.<br /><br />c/6<br /><br />Hooty
 

ToStev

Recruit
Joined
May 24, 2003
Messages
5
Re: Mercury 75HP unwilling to go to high gear

I went to mercurypartsexpress.com and they do not sell the wiring harness (in my zip code).<br />Does anyone know anywhere I can check?
 

Hooty

Rear Admiral
Joined
Oct 2, 2001
Messages
4,496
Re: Mercury 75HP unwilling to go to high gear

Give these folks a try.<br /><br /> web page <br /><br />c/6<br /><br />Hooty
 
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