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#1787753 - 06/01/20 03:37 PM Re: Repowering Mercury/Mariner 18 & 20HP XD engines to 25hp [Re: onthewater102]
onthewater102 Offline

Member

Registered: 04/14/05
Posts: 1649
Loc: Kent, CT
I've got the original WMC 20hp carb sitting around in the basement, if it does you any good. I can check the casting # if you're interested.

I don't know about any modifications swapping from Tillotson to WMC, Boat_Head's description is certainly detailed enough to follow if it's right, but finding the reed block might be its own issue.

This is the carb I had originally:

https://www.boats.net/catalog/mercury/ou...-12-24-25-26-27
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#1787814 - 06/02/20 09:59 AM Re: Repowering Mercury/Mariner 18 & 20HP XD engines to 25hp [Re: onthewater102]
Boat_Head Offline

Member

Registered: 04/12/05
Posts: 207
What I did before my upgrade from Tillotson to the WMC (Walbro) was to compare the parts listings for the fuel section of the engines (1980 vintage to I think 1985) via on-line vendors. From there I learned what parts were needed. IIRC, I got a used flange behind the carb and ahead of the reeds and a used reed body from a WMC-carbed motor. I think I had like $250 invested in parts total. The biggest pain is the grinding of the cowl "hook" to allow the carb to fit. The rest of it is bolt-in.

Now, if/when you do go the WMC route, you will need the plastic pieces on the front of the carb (not the inlet silencer as it won't fit under the cowl) that allow you to prime the carb when cold, etc. One can find these pieces on the Bay of E, but it might behoove you to purchase them new as what is typically sold there is worn. I did not opt to get the piece that guides the primer knob on the motor cover and mine just protrudes from the same hole that the Tillotson knob does.

This is what I think you have:
http://www.marineengine.com/parts/mercur...block-and-cover

This is what I think you need:
http://www.marineengine.com/parts/mercur...-serial-group-1

Notice the carb mounting flange is different.

The pieces in front of the carb inlet as found here are what I used:
http://www.marineengine.com/parts/mercur...a/carburetor-25

Good luck, keep that motor running!

I should probably post pictures and this might give me an excuse to learn how to do this.
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#1787827 - 06/02/20 11:47 AM Re: Repowering Mercury/Mariner 18 & 20HP XD engines to 25hp [Re: onthewater102]
onthewater102 Offline

Member

Registered: 04/14/05
Posts: 1649
Loc: Kent, CT
Those links don't look like you're trying to convert an XD series motor, that's why you're having to source more parts than a simple carb swap. Best bet would be to find a seized power head to cannibalize, otherwise economically it's not going to make much sense to be bothering with it.
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#1788306 - 06/06/20 06:30 PM Re: Repowering Mercury/Mariner 18 & 20HP XD engines to 25hp [Re: onthewater102]
Boat_Head Offline

Member

Registered: 04/12/05
Posts: 207
Yukonboat, you have another option, but it might not be to your liking.

Since the likely issue you have is ethanol in gasoline (I prefer it in martinis), remove the ethanol from the gas. Google it. I have been doing it for what seems like 10 years now.

Quick summary of what is required.

* Get 93 octane gas
* get a bunch of PET juice jugs, like quart size.
Time to trust me on this
* put an inch of water in the juice jug, fill the rest of the way with gas.
* shake like crazy (ethanol is in solution in gasoline but bonds with water, SCIENCE!)
* let it set for a day
* CAREFULLY decant the gas from the phase separated mixture at the bottom.
* CAREFULLY decant it again, looking for the water "marbles" at the bottom.

What remains is about 90 octane gas, sans ethanol. You will know that the ethanol has been removed by the fact that the level of water (really no longer water) in the bottom of the shake jug has increased in size.

Remember, you are working with an incredibly volatile substance and respect for same is required.

By the way, you will get something like a 10% gain in power as ethanol is basically a filler compared to gasoline. This is equivalent to buying gas before it was polluted by Washington and the corn lobby. Still preferable over MTBE, though. Your 18hp Kiekauffer (sp?) Mercury will love you for it.

Like to hear from you. Looks like you are new to the site from a membership standpoint.

(My left hand is arthritic. Typing, to a point, is therapeutic.)
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#1788335 - 06/07/20 09:28 AM Re: Repowering Mercury/Mariner 18 & 20HP XD engines to 25hp [Re: onthewater102]
Don P Offline

Member

Registered: 05/03/07
Posts: 18946
Loc: CLINTON, CT
For a small engine wouldn’t it be easier to buy the metal 5 gallon jugs of ethanol free fuel???....than to do all of that “decanting” with 1 quart containers. That seems like a REAL pain in the a$$.

I have a 106 gallon tank so I just pump what they have at the docks, use Stabil fuel stabilizer every time I get gas, and cross my fingers. 4-6 years ago I had a problem with bad fuel from docks and had to have my marina pump out the last 35 gallons of my tank. Other than that 1 episode I’ve never had a fuel problem (knock on fiberglass).

I believe cat_in_the_hat buys and uses the ethanol free fuel metal containers for his small hp tiller on his 14’er.
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#1788400 - 06/08/20 07:43 AM Re: Repowering Mercury/Mariner 18 & 20HP XD engines to 25hp [Re: onthewater102]
Boat_Head Offline

Member

Registered: 04/12/05
Posts: 207
Yeah, it is a bit of a pain, but with a small eggbeater, one doesn't need much. Not sure what a 5-gal jug of ethanol free fuel goes for, but I know that the smaller cans are rather pricey.

Where does one get said 5-gal jugs?
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#1813334 - 05/04/21 09:32 AM Re: Repowering Mercury/Mariner 18 & 20HP XD engines to 25hp [Re: Boat_Head]
drewski69 Offline
Member

Registered: 05/02/21
Posts: 1
My Frankenmotor has a 25hp carb on when used to have the 18hp one. Same the throttle cam/linkage was adjusted for the 25hp setting. The idle timing was set something like 5-BTDC whereas the 18 was something like 2-ATDC. My boat (Abalone, a 14-ft Duranautic), is now wicked fast and I like to race dual-motor Regulators on the CT river. Scary and I always lose, but it is a lot of fun.

USE NGK PLUGS!!!

Boat_Head [/quote]



First of all, HUGE thank you for posting this. I bought a 16 footer tin boat I'm planning on turning into a budget duck/fishing boat for me and some buds. The guy that sold me the boat last minute threw in a 1985(?) 18xd because he hadn't run in forever just sitting in his garage and wanted it to get some use. Got er runnin strong and it does push the boat pretty well, but I'm worried with 2 more guys and duck gear it'll need a little more juice. I am definitely interested in tinkering to squeeze more power out of this thing without having to buy a new motor.

It currently has a WMC9 Carb, after reading these posts I am trying to find a 25hp carb to put on this, but it looks to be in the $200-300 price range and I cant find anything used.

Does anyone have a list of part numbers for carbs that I could use on this to make the search easier?

Unrelated to power, does anyone have any idea how to convert this over to remote throttle? this pully system is so jacked up. Is there an adapter plate somewhere out there or is there a way to do it that I cant figure out?







Edited by drewski69 (05/04/21 09:39 AM)
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#1813790 - 05/12/21 05:21 PM Re: Repowering Mercury/Mariner 18 & 20HP XD engines to 25hp [Re: onthewater102]
Boat_Head Offline

Member

Registered: 04/12/05
Posts: 207
Sorry for the late response.

My 25hp carb is a WMC 31. A WMC 31A also works and I think the difference is that one component is made from a different material. The models past that aren't as easy to swap in, but I could be wrong. YOu will have to reposition the throttle cam when installing the 25hp one. The roller lines up with the forward line on the cam in your picture. This also means you have to adjust the dashpot.

You will likely NOT find a reasonably priced one in decent shape during the boating season. You have to start looking on the web in the fall, when others start parting out older motors.

Word of advice. If the price is right but the carb looks like sh!t, it will be. Be patient or just go for it with one that looks good. Still rebuild it.

By the way, it looks like your primer handle is broken off. Recommend replacing it when you get a chance.

[https://greenbayprop.com/wmc16a-mercury-mariner-25xd-outboard-carburetor-assembly-gb608139238]
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