20/25hp carb number difference

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scoobeb

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Ok,here we go on this carb issue i have.I have a 1993 20hp 2 stroke merc with the original carb of course which states the number 32 on it.I look at the 3 different carb numbers online and there is WMC 31/32A and plain 32.

All 3 carbs seem no different as in what the schematic shows,i mean no difference.So i upgraded from the 20hp carb to the 25hp carb,the yrs were almost the same,the used carb i got was from a 94 and my carb was from a 93 but i mean they are 100% identical except for the bigger bore for more power but here is what i noticed.The 20hp carb i have says it's a 32 and the carb i just got says it's a 31A but they are 100% identical from what i can see.My question is what is the difference between the 32 and 31A if they look i mean identical besides the size of the bore.I called the place i was going to buy a new carb from and all 3 numbers come back to the same schematic which shows the parts to be identical so what's with the number difference?
 
Different casting for the bigger bore. Take your S/N and a S/N off a 25hp and look up the component parts & you'll see they have different sized jets & several other differences...the 25hp carbs are cheaper to find rebuild kits for too...

BTW you need to synch your motor and adjust your timing advance after swapping the 20hp for 25hp carb. Other than that you're good to go.

Perform these procedures (starting in the lower right corner of the 1st page section 6-15) only in a test tank or on the water, never with muffs on the motor.

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Come to think of it, I believe you'd mentioned on a different post that your 20hp ran like an absolute beast - assuming I remember this correctly I wonder if for some reason you had the larger .080 jet in your 20hp.
 
I just talked to the maker of the WMC carbs and he told me the carbs are basically identical all the way around,I also asked if I needed to do anything else to upgrade in which he replied,no. I asked about the timing also and he said you don't need to do a thing but switch the carb out. The 2 carbs have the same jet also he said,0.80. Once I install it I will test run it to see if there is a significant difference in mostly torque is what I expect, overall wot speed should creep up a bit but I'm not expecting much.
 
I pop my serial number in and it's the same carb just a different internal bore as u said. Boats.net has it,0D202003,check it out.
 
So my plan is to completely rebuild the carb today and test it out next week.
 
I did the conversion already on my motor - Mercury tech support was where I found the factory timing settings are different between the 20hp and 25hp models, I did need to adjust mine to get the 25hp setup to idle smoothly, but I think my motor had other gremlins that happened to get ironed out at the same time as the swap.

These carbs are so simple that unless there were bore differences in the port from the jet to the throat there really isn't much else for there to be different besides the throat. Easy enough to test with a small drill bit if you're so inclined.
 
That's funny,gremlins ironed out. My 20hp with the 20hp carb I mean idles like a 2 stroke but it idles like a dream. The only other 2 strokes that idled better than this motor was the 15hp merc and yamaha I used to have. The 15hp merc 2 stroke was an unbelievable runner for it's size,it had so much power and I wish I would have kept it forever. It idled so smooth you would of thought it was a 4 stroke, that is how great it ran.

As far as the 25hp carb, I'm going to completely rebuild it as I said and install it probably tomorrow or in a couple days. I talked to a merc dealer today and I got 2nd confirmation not to mess with the timing whatsoever. He said the carb swap will not effect a thing. I watched many 9.9hp johnsons upgraded to the 15hp by simply swapping out the carb,never touched the timing so I will install the carb,fire the engine up and if it runs great at idle I will throw it into gear and Rev it from idle to wot fast to see how she sounds,if she runs good then I know I got my money's worth. Like I said,I don't expect miracles, just a boost in torque and maybe a few mph gained at best,I get that I'm a happy camper.
 
The original carb for my motor was disassembled and mixed with other carb components from a chainsaw and god knows what else in a kid's sandcastle pale when I bought it...I found all sorts of delightful surprises when I went through putting the motor back together but for some reason I neglected to look into the timing until I swapped out to the bigger carb. Bugs me that I didn't know to do that originally - I have almost as much money into the original carb as it took to replace it.
 
I was going to go brand new on the carb but at the $320 price tag and on backorder with no release date in sight I started to look used. I have $90 invested in the carb and I bought a total repair kit which covers everything but a new float. Here is pics of the used carb I just got,seems to be in tremendous shape and extremely clean.
 

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I haven't even cleaned it up yet or gutted it yet. The inside of the bore looks like new,looks to be a great deal I got but we will soon find out when I open her up for surgery, lol. Hey if I gain a good amount of torque and say 2-3mph at best,imo at what I spent the upgrade would be well worth it. Imo the torque alone is worth $90 as I fish very shallow areas with rocks and tons of oysters so I need to be on plane in a jiffy,plus I just gained 500 rpm . With more power I can now sling a 14 pitch prop to,so that should give me a few mph and still not suffer any in hole shot. I can't wait to see the difference.
 
UPDATE, well my motor is finally a true 25hp with the new carb installed. I just need to fine tune the fuel air mixture screw on the lake when it recedes down more. My local lake is so high from the rain from hurricane hermaine. It ran great on muffs after messing with it for a few minutes. Now I have a ton of black exhaust goo coming out of the prop which tells me it's running extremely rich.
 
Side note, since we have the same setups...if your cowl seal is shot seeing as it's no longer available you can use 1/8" adhesive neoprene to make a replacement and it works beautifully. Just make sure you're getting one that's fuel/solvent & heat resistant.
 
Thank you for the info. Fortunately my seal is not dry rotted like 99% of all the 20/25hp mercs I have ever seen or ran. My seal has a very,I mean very minor tear at the top of the front of it but it's so small it's hardly noticeable. Like I said it's just so hard to find any used outboard to begin with that has a nice seal but I just got all around lucky with this engine. All it needs imo is a touch up fresh paint job which I will do and now I'm going to replace the 20hp decals with these I mean really nice American flag with an eagle type of decal I found on ebay. They are so sweet looking and will make my motor look so sharp. I just have to make sure I get them to fit my outboard. It's an older outboard but I promise u one thing,it's so clean and runs so good it will be difficult to ever get rid of it. I will never sell it unless I got what I think it's worth because finding one in this condition is near 0% -5% at best in my area anywy.
 
If say I decided to replace it in time if it wears any worse than it is,were would I find this stuff your talking about, and how do u stick it to the cowling itself because i know they used staples for the original rubber.
 
Since u have the same outboard as me,were do u find your fuel/air mixture screw to be at the best setting. From lightly seated out to 1 1/4 turns cc is the starting point, I have found that at a hair past 1 1/2 turns is where my outboard runs best. How about you? I'm heading down to the lake this week I hope to give her a test run to make sure that this carb works properly and to tune it to perfection.
 
i found the neoprene through amazon, but on my motor there were no staples holding the seal between the upper and lower portions of the cowl, it was just adhered to the rim of the lower section, wrapped over the top edge and then back down on the inside roughly 3/4" on both sides.

I can't help you much on the carb adjustment - I know it didn't take me much fiddling with it, unlike my god forsaken string trimmer for the yard, I don't think it was a full turn from the starting point, but I couldn't even tell you if I started 1.5 turns out from seated or 1.25, I just know I started wherever the service manual indicated.
 
I think at 1 1/4 - 1 3/4 turns,in between there is usually were they run best,at least the last 2 I had.
 

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