Mercury Wmh 34/39 Carb black cap/plug

Hey everyone I took my wmh34 carbs apart to clean and inspect because my motor (2.5) wasnt getting over 3k rpm. I did find the float adjustments were off and one needle valve was stuck so I am hopeful.

Long story short wrecked top carb on accident and got a wmh39-1 replacement. While making sure all the jets were correct i noticed these black caps/plugs in the bottom of the top side of carb. These were not installed in the wmh34 carbs but someone was in them previously.

Figuring I need these i ordered two repair kits however the kit only comes with 1 cap/plug. Do i need 2 for each carb? Do i need any of them? What are they? The picture only has one installed crooked for easy removal and to show the port underneath on one side, but there was 2 caps/plugs when i opened the carb.

Welcome to the forum, Jay. I am not sure about the black caps but I’m sure somebody else will be. If it’s not getting over 3000, that’s often times a stator breaking down. There is a high speed and a low speed side to the stator and normally the transition is right around 3000 RPMs just for what it’s worth. Might not be your carburetors but it’s always a good idea to go through them.

Hey sauger thanks for the welcome. I've read through a bunch of posts with yourself and some others so ive seen how much knowledge a bunch of you have on these motors and set ups. Fingers crossed someone has run into the same thing. Im not really a carburetor kind of guy, they are actually something i have had little success with. So just really trying to run through them with an eye for detail (not normally my style haha).

Anyway i took a closer look at what it is connected to circuit wise. Those little pin holes come out into the chamber of the top of the carb but in the chambers on the inside looks like it doesnt really go anywhere. The manual calls this the off idle circuit more specifically the off idle discharge holes. Just for more info.

Pic of manual

While we are waiting on others to chime in, ohm out your stator. The 3k thing is standing out in my mind…. Did it used to run ok?

Have you yanked the black boxes? How old are your switchboxes?

Unfortunately i know pretty much nothing about the motor or the history of it besides i tested and had good compression on all cylinders. And that i could fire the motor up every time i tried no problem idled like a charm. Go to give it throttle it just falls on its face 2500-3000 rpm. If i choke it while accelerating i could get another 1k rpm. This is what lead me to the fuel system.

The guy i bought it off of actually had mentioned something about he thought tge reed valves were bad so in combination with the behavior i just said ima rebuild the fuel system clean carbs and replace reed valves with some carsons.

So fuel system is rebuilt. Reeds are in. Carbs are clean and just waiting to be put back together.
I will definitely check out the electronics before testing motor too, thats more up my alley anyway lol.

Also i guess maybe an important note not sure motor started life as a 98 EFI but was repowered with a carbureted powerhead since based on tge wmh34 carbs id say 93-94.

Were the reeds steel? Any chipped or broken? I have the ccm reeds too. Love ‘em.

Also rebuild your little pulse fuel pump if it has one. Be sure to set your float levels by the book

Funny enough i was talking to chris after i pulled the reeds and they werent metal but a black plastic/fiber he thought they were probably boysons. I dont know if the previous owner had doubt about if they were for the right motor or not but they seemed almost new.

Do have a question for you regarding float adjustment height. I think in other posts you or someone had mentioned 1/16th of an inch past top of bowl. The manual states even with the top of bowl but does not specify with or without gasket. So is that 16th to account for gasket height?

Probably just the difference in carbs on the sixteenth of an inch I have wh46’s. Follow the manual for those carbs.

rebuild your pulse pump too, if you have one. Make sure ALL fuel line is replaced with new good stuff. Also the little rubber line that activates the pulse pump.

Yeah i got the whole kit for the pulse pump. And sounds good ill follow the manual for height adjustment.

Follow the details on link n sync when you get them all back on your motor. What boat is this on?

I dont see any reference to a link and sync in the material i got. You have a reference? I didnt take the throttle linkage apart just took the throttle plates off and slid them out. But will be good to make sure all is good on that front.

This is on a 98 nitro savage 20ft love the boat even though its a bit beat up if i get the motor running good ill dump some money into some body work and carpet. Redo the electronics and she will be an awesome ride.

https://www.google.com/search?q=merc...t=gws-wiz-serp

check this. Very important. Gets mechanicals and timing all playing nicely