1991 Merc 40 Questions

[Bill kubiak]

Just bought a 1991 13 ft Boston Whaler with a 1991 Merc 40 with trim/tilt
I cannot find the motor ID plate, where is it hidden?
What size prop should it have, the prop on there looks small?
What is the WOT rpm supposed to be for this motor?

no, I have not gotten a manual yet, my west marine is out of them until next week

Seems like a good motor, fires right off, idles decent, pulled the plugs, two were cruddy, two were clean. Cleaned them all and stuck em back in for now
Lower oil clean, almost too clean, gonna take it out for a test run in a little while, will check that oil after and do a compression check then

 

[carholme]

Re: 1991 Merc 40 Questions

Bill;

The first thing to do is get the s/n:

http://www.iboats.com/basics/serial_number_year.html

or on the powerhead a disc like this:

http://img84.imageshack.us/img84/8224/391496208.jpg

Gerry

 

[Maxz695]

Re: 1991 Merc 40 Questions

View attachment 94433View attachment 94434 My 40 HP came with a 12 pitch prop. It did good on the speed but wasn,t getting the RPMs right I went from 4800 - 5000 RPM by dropping 1 pitch to 5300 - 5500 RPM. I put on a bigger prop with less pitch. 12 X 11 pitch. Most 40 HP come stock with the 12 P Prop. This item sold on ebay. The original Prop last night. It,s on the way to the post office. I don,t know if you have 4 stroke or 2 stroke 40 HP but if your under RPM you need less pitch. if your over RPM you need more pitch and possibly a larger diamiter. A 12 P seems right for 13 to 14 foot boat depending on your average capacity of weight . Get your RPM reading under your most use load and go from there. (Light Medium or full capacity may make a big diffennce in your choices

 

[Bill kubiak]

Re: 1991 Merc 40 Questions

It's a two stroke 40 hp 4 cylinder
I see a spot on the side of the transom mount that looks as if it was painted over at one time, where on the motor do I look for that plug with the serial number on it.
We took the boat out this morning for the first time and ran great, good hole shot, but top speed with two aboard at WOT was 32mpoh gps
The tach does not work, I have another tach from a V-8 mercruiser that I think works, I will set it for this engine and connect it and see it works

 

[carholme]

Re: 1991 Merc 40 Questions

Bill;

Here is the manual: P/N 90-814676R1

http://1manual.com/Mercury manuals/Service Manual PDFs/TwoStroke/814676r1/cover.pdf

You must have Adobe Acrobat reader installed to use this manual. If you scroll down to the lower part of the opening page, you will see the various engine components in red. Click on the one you want and when the first page opens, click on the "Save As" icon at the top LH corner of the page and you can save it to your computer.

Parts listing:

http://www.crowleymarine.com/mercury-outboard/543.cfm

Gerry

 

[Bill kubiak]

Re: 1991 Merc 40 Questions

I found this serial number on a disk behind the remote control plug on the side of the motor OG554810, what does that tell us

 

[carholme]

Re: 1991 Merc 40 Questions

Bill;

That s/n comes up as a model:

1040412TD MERCURY 1997 40

Previous manual and parts listings in post #2 above are correct for that s/n.

Gerry

 

[Bill kubiak]

Re: 1991 Merc 40 Questions

it's a 1997 motor? Wow all this time I thought it was a 1991

 

[Bill kubiak]

Re: 1991 Merc 40 Questions

What are the symptoms of a bad stator?