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engine idle problems 1987 40 hp

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cabu1966

New member
I have a 1987 mariner 40 HP outboard that would not stay running on a recent fishing trip. It ran fine for 2 days, but by the end of the second day I was headed back in and noticed it sounded like it was decreasing in RPM's. The next morning I started out and it died. Each time I would crank it, it would idle about 5 seconds and die. I got it home, and pulled the "out" hose on the fuel pump and pumped the bulb. At first nothing came through, but then fuel shot out and I could hear air being pulled back in the fuel pump. I also checked the fuel filter and it was clean. So I hooked everything back up and fired it up. Now the RPM's are way to high on idle. I don't have a tach, but I would guess about 3000 RPM's on idle. I have tinkered with the throttle stop screw, but it has not changed the high idle. I am at the end of what I can think of. I'm not against taking it to a shop, but would like to be able to fix it myself. I have a SELOC manual and could start to disassemble the motor, but would love to know if someone else has an idea as to what could be wrong.
 
Re: engine idle problems

The first place that I would start would be a good carb clean. Get the complete rebuild kit, and rebuild the fuel pump. Sounds like the carbs are possibly sticking open, and you should not have anything sucking backwards on the fuel pump. This indicates a broken diaphram.
 
Re: engine idle problems

Well i ran seafoam through it this weekend and that didn't improve things. Pulled the throttle cable loose and everything idled at proper rpm with a little tweaking. So I have a bad throttle cable, but still misfiring and backfiring bad. Think I may have to take it in at this point, as it seems beyond my basic abilities.
 
Re: engine idle problems

I will try this over the weekend. I also have a friend that is going to help me pull the carbs this weekend. My new question is, for the Mercury 40 ELO serial number 6E9 L 428686, should I be buying a Yamaha 18-7740 carb kit, since it is my understanding that Yamaha built these for Mercury? When I changed the lower unit lubricant after I bought the motor, the Mecury dealer gave me their standard vent plug and drain fill plug and washers. These did not fit my outboard, nor did the pump that came with the Mercury gear lube.
 
Re: engine idle problems

Yes, this is a Yami built motor - the "C" model Mariners are (mechanically identical) to Yamaha's own 40FE/FM models (81-83 model years).

You can use a Yami carb kit if available or go to Merc and get a Yami kit rebranded for Merc and pay the premium...

Sorry, I don't have a cross reference to the Merc part number (17068M) which sells for a little over 150 bucks, my Yami parts lists don't go back past 1985...
 
Re: engine idle problems

Thanks for the info. One question though, you said that your Yami parts lists don't go back past 1985. What year model would the above serial number be? I was thinking it was a 1987 motor, but I could well be wrong since I can't find where I got that information. Just want to make sure I am getting the right parts.

Thanks.
 
Re: engine idle problems

Yes, it is a 1987 "Mariner" model, but that does not corrolate to the Yami model.

Yamaha discontinued that model in their own brand in 1983.

They continued to produce the "discontinued" model for Merc (as a Mariner) for 9 more years with the final run in 1992.

So even if you had a 1992 "C" model Mariner, what you really had was (at best) a 1983 Yamaha.

When Yami stopped their run in 1983 there was no technical advances or improvements to the model they built for Merc, they simply used up "left over" parts.

So while the motor was not poorly built by any means, it was simply "early 80's" technology. This allowed Merc to keep the price of the motor low in comparison to "new" motors which made them attractive to consumers on a budget.

Bottom line, if you are going to use Yami branded parts, you have a 1981-83 model, regardless of the "Mariner" year....
 
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