A4 Fuel Leak

[Marian Claire]

Just to be clear. Is it not more determined by the type of carb vs type of engine. Early vs late. We have many "mixed" engines out there. My understanding is that the early carbs had internal passages that did the same thing as the scavenge tube. Is that correct? I have an early carb and no scavenge tube.
Dan S/V Marian Claire

[ndutton]

The scavenge tube was common on early engines. Later engines did away with it.

Is there a source available for this information?

My information (cited below) is the scavenge tube was never done away with. In fact, if our engines were manufactured today they would still have it per USCG requirements.

33 C.F.R. Subpart J—Fuel Systems
Title 33 - Navigation and Navigable Waters

Title 33: Navigation and Navigable Waters
PART 183—BOATS AND ASSOCIATED EQUIPMENT

Subpart J—Fuel Systems

§ 183.526 Carburetors.
(c) Each updraft and horizontal draft carburetor must have a device that:

(1) Collects and holds fuel that flows out of the carburetor venturi section toward the air intake;

(2) Prevents collected fuel from being carried out of the carburetor assembly by the shock wave of a backfire or by reverse air flow; and

(3) Returns collected fuel to the engine induction system after the engine starts,

[Dave Neptune]

Tube good!

All of the A-4 carbs have a scavenge tube. If you don't it's not a marine carb or for the A-4. The early cast iron carb had an internal one and the two "new style, 4 & 5 screw were equipped with an external one. I have seen a few that were removed and plugged~absolutely not a good idea. Many stationary duty motors with updraft carbs also used them as a fire safety precaution.

Dave Neptune

[edwardc]

OK, my $.02
The scavenge tube was common on early engines. Later engines did away with it. ...

Are you sure you're not thinking of the valve lifter galley oiler? Early engines had a small dia metal tube, visually similar to the scavange tube, connected from an oil port to a fitting on the valve lifter galley cover plate. Later engines did away with this.

[domenic]

Al, are you saying that the later Atomic Four engines were delivered with no scavenge tube?

I had not heard that before.

My A4 is a 1968. It does not have a scavenger tube. Mine must be the female model of the A4.

[Dave Neptune]

Double check

Domenic, what carb are you using? I'd get one before you get boarded as they are std equipment on all A-4 marine engines.
If you have either of the late model carbs there is probably a plug in the carb and the manifold port for it. On the old cast iron carbs it is there but it is internal and vents to the manifold side of the carb base.

Dave Neptune

[Marian Claire]

Thanks for the confirmation. The MC is safe and legal with the early style cast carb, internal scavenge tube set up. Another twist to this, as far as I know, is that the early model manifold does not have the port for the scavenge tube pre tapped. Why would it. So anyone with a true early engine that added a late carb would have to create a port for the scavenge tube. The early manifolds have a "spot", it is just not tapped. You could also use the spacer from MMI, a much easier adaptation. So just check and see what carb you actually have and make it safe. Dan S/V Marian Claire

[Golfdad75]

Size of carb main plug washer

Anyone know the size of the hard washer that fits the main plug on the carburetor

[Dave Neptune]

Golfdad, I don't know the size off the top of my balding head. Most good hardware and /or parts houses carry a variety of "fiber sealing washers" so with the "plug screw" you can find the proper size. Buy a few and keep them in your ditty box.

Dave Neptune

[Golfdad75]

Copper washer

A mechanic suggested a copper washer on the main plug in the carburetor. Any thoughts?

[TimBSmith]

I would suggest buying the service kit if you have late model Zenith..

https://moyermarine.com/product/carburetor-zenith-factory-service-kit-fcar_594/

When I cleaned/rebuilt my carburetor this fall I bought the kit above and it has the gasket you want and many others as well as other basic service components. $35 (if the kit is right for your carb). Even if it is not, I will wager that one of the smaller diameter fiber gaskets will do the trick.

After spending a lot of time sealing a fuel-related leak on my Racor fuel filter bowl, I would not use copper or anything other than the small soft fiber gasket that seats so nicely and reliably seals in the main passage, so much so that it likes to stay stuck in the passage after the bolt is removed.

In fact, during my carb clean/rebuild the passage gasket did not want to come out and I used a small pick to gently displace it. My vote, buy the kit, use parts that fit. Happy Holidays. Stay well.

[TimBSmith]

Also just found this thread which may give you an alternative to kit...

https://www.moyermarineforum.com/forums/showthread.php?t=4547

Looked in up here:

https://www.mowpart.com/271716-briggs-stratton-washer-sealing.html?gclid=CjwKCAiA_Kz-BRAJEiwAhJNY70oGZi4fCKVqiXZP7DK-dgtIJ9mta2Mv91S7V7J8OWoQHKjbT383rhoCgysQAvD_BwE

Solve the problem, save some money. Stay well.

[JOHN COOKSON]

A mechanic suggested a copper washer on the main plug in the carburetor. Any thoughts?

Copper and aluminum in a "marine environment" sound like a perfect set up for electrolysis. As I recall aluminum is the sacrificial metal.

ex TRUE GRIT

[Dave Neptune]

Copper ring seals

No copper. Copper sealing rings are used on banjo fittings as the bolt and the base are steel so the copper crushes and seals. The copper can cause the aluminum to distort (crush) and may just seal. But the next use won't seal as it will be almost impossible to match the pieces in the same EXACT position.
Then there is the electrolysis issue.

Dave Neptune