Something missing on top of the carb?

[justin65]

Tillotson, model #WB3A

Does anyone know what is supposed to go in the hole on top of the carb?
The hole is directly over the Idle adjustment screw.
The repair books I have don?t show a break down of the carb and the rebuild kit (instructions) I just got shows something but doesn?t name the part.


Thanks

 

[steelespike]

Re: Something missing on top of the carb?

That would be a plug.Sometimes refered to as a soft plug.

 

[roscoe]

Re: Something missing on top of the carb?

WB3A is a Walbro carb, not a Tillotson.

Diagrams of the carbs are on mercruiserparts dot com

Missing part is a cap plug.

As always, please list the make/model/year, of the motor you are working on.

 

[Frank Acampora]

Re: Something missing on top of the carb?

It is called a welch plug and is usually brass. It is used to seal a hole the factory needed to drill in order to install the thin brass tube that supplies fuel from the bowl to the low speed atomizing circuit. Although it is small, it is very important to the proper operation of the carb. Without it, the low speed circuit will draw mostly air through the hole and the engine will run lean--both at low and high speeds. Whatever you use to plug the hole, don't go too deep or you run the risk of either sealing off the end of the small tube or restricting the fuel flow.

If you look at the back of the carb, in the casting up top near the butterfly you will see 1,2, or 3 small holes, depending on carb model. These meter fuel to the engine at less than approx. 1/4 throttle when there is not enough air flow through the venturi to suck up fuel through the main delivery pipe (the large brass tube). One hole will always be between the butterfly and the manifold and delivers fuel at idle when the butterfly is closed. At off idle more holes will be exposed to manifold vacuum and deliver the extra fuel required by the engine at these slightly higher speeds. The low speed needle regulates the amount of air and fuel delivered at idle. Because this circuit is always exposed to manifold vacuum, it delivers fuel at all times. Thus: if you set it too lean, it will affect fuel /air ratio at full throttle also. Do not probe these holes because they are drilled to a precise size to properly meter both fuel and air to the engine at low speed. If you have removed the butterfly, the edge is beveled in one direction. Be sure to install it correctly.

Since all Chrysler/ Force carbs that I have seen in this size have serials beginning with WB, I suspect that both Tillotsen and W al B ro are made by the same company. They seem to use the same base casting with only minor differences in other parts. Therefore if you look up Tillotsen and ask for a welch plug, they might be able to supply you with one.

 

[justin65]

Re: Something missing on top of the carb?

Thank you for your replies.

Frank all this old Marine can say is wow!
I wish I knew what you have already forgotten.

I checked with Napa (place I got the rebuilt kit) and they don?t show any plugs small enough to fit. I was wondering of I could make a small flat plate to silicone over the hole without allowing any silicone to enter the opening?

 

[Frank Acampora]

Re: Something missing on top of the carb?

Yep, you can do that just be sure everything is sanded clean and bright. I would personally prefer JB Epoxy or something similar. Just be sure to use it sparingly so none goes in the hole and onto the needle.

Sometimes I get a little long-winded, but I love to BS about all things boats

It is also my personal philosophy that if someone learns how something works and why it works the way it does,they can then use logic to fix problems. It also annoys the hell out of me if a manual just says "do something, or don't do something" and doesn't give a reason. And I thing most people feel the same, so I give as much relevant information as I think necessary.

BTW--I see that that casting has no choke shaft thus I deduce that it is off a newer engine with an enrichment solenoid for cold starting. Correct? And when you reinstall the float, if you hold the carb inverted, the weight of the float should hold it parallel to the casting. I think the manual calls for 13/32 but I always use the parallel setting.

 

[justin65]

Re: Something missing on top of the carb?

Yep, you can do that just be sure everything is sanded clean and bright. I would personally prefer JB Epoxy or something similar. Just be sure to use it sparingly so none goes in the hole and onto the needle.

Sometimes I get a little long-winded, but I love to BS about all things boats

It is also my personal philosophy that if someone learns how something works and why it works the way it does,they can then use logic to fix problems. It also annoys the hell out of me if a manual just says "do something, or don't do something" and doesn't give a reason. And I thing most people feel the same, so I give as much relevant information as I think necessary.

BTW--I see that that casting has no choke shaft thus I deduce that it is off a newer engine with an enrichment solenoid for cold starting. Correct? And when you reinstall the float, if you hold the carb inverted, the weight of the float should hold it parallel to the casting. I think the manual calls for 13/32 but I always use the parallel setting.

I made a small plate using 1/16" thick aluminum. About 3/16" in size.
I'll get some JB wield and secure it the way you mentioned.

You?ll never hear me say you?re long winded. I know next to nothing about boats and I can relate to explaining how something works in order for people to better understand how to fix the problem. If only more people took the time to listen and learn.
My biggest problems with manuals are I can?t get enough information.
Its nothing like the Military where you have exact procedures for any repairs from a radio to an APC.

It?s off a 1969 Chrysler 35hp #3551. With one of the model numbers from Mars.
I have yet to find a parts place that doesn?t tell the ?They didn?t make that model? But I know my cousin (who I got the boat from) went thru the same thing. But yes it has the
Solenoid that?s activated by pushing the ignition key in.

Thanks again for talking the time to explain the ?what? and the ?background? of the hole. I?m off to the store for the JB wield.

Also wanted to ask you what manual is the best for these motors?
I have the factory, one from interactive and one from Clymer (? Spelling)
Is something better out there?

Thanks again buddy..