A4 Fuel Leak

[Richie740]

Hello all, this is the first new thread on the forum but I've already seen great feedback from all you members so I'm hoping I can get some great advice here too

I started having what I believe are fuel issues a couple weeks ago on my '77 C&C 29. There was old fuel from the previous owner and then I placed some new fuel in the tank but let her sit for about 6 months on 1/8 tank so I thought of condensation. I've bled the fuel line via the Main Passage Plug and changed out the fuel/water separator filter. In doing so I've got the engine running better but in my troubleshooting I created a fuel leak (I also think that this leak helped removed some of the water in the fuel which dumped into my bilge )

I originally thought that the fuel leak was coming from the main passage plug because that gasket was shot but after thoroughly checking that out I have determined that the likely culprit is a copper pipe running from the bottom of the carb to the up to the engine block above the carb via copper elbows. Someone in the marina has mentioned to me that I should remove this part altogether and plug the 2 holes with special plugs that can be installed. He mentioned that this was a bad design and actually causes vacuum issues. Can anyone confirm this for me because I don't want to just start removing parts off the engine that were designed to be on it?

[Dave Neptune]

Leaks

First welcome to the Afourian Forum. Second ignore that guy!!!

Do not remove the "scavenge tube, it is a safety devise and very important!!!

What you probably have is a leaking needle&seat. This allows fuel to over-run the bowl and fill the carb throat. The scavenge tube removes this fuel (hopefully while running very rich) from the throat via manifold vacuum. When the engine is not running the fuel can leak out of loose fittings or the front of the carb until empty.

Get a shut off valve for safety installed inline too.

Dave Neptune

[romantic comedy]

You can check the level of the fuel in the carb without removing it.

You need to find a way to hook up a clear tube to the bowl. You can use either the drain of the main jet plug. You remove the plug, and find a fitting of anything, that will let you hook up a clear tube in its place.

Then you route the tube up. It need only be a few inches long, and open at the end. You run the engine, or just have it so the bowl will fill. Then the tube will fill to the same height as the gas in the bowl. This way you can see if it is filling to high. It should fill to a height less then the carb joint.

I have not done it on the Atomic Four, but many other carbs.

[ndutton]

I have two comments:

1. Dave covered the first. I will emphasize that the tube is there for safety and is a USCG requirement.
2. "Someone in the marina" would do everyone a favor if he shut his pie hole. In this case his advice was dangerous, even potentially deadly.

[Richie740]

Thanks everyone for the replies and suggestions. It's interesting the comments that I received because I questioned removing this piece of the motor myself. The problem I have here is the guy that suggested this wasn't just some schmuck in the marina but rather one of the guys that runs the boat yard in the marina and likely the guys that are going to repair my fuel leak if I can't work it out myself

I'm going to the boat today to try and investigate a little more and I'll probably pull the carb (never done that before but it doesn't look like too difficult of a task). I'm thinking that at the least it needs a good cleaning and potentially needs to be rebuilt.

[edwardc]

Chances are that your boatyard expert is unfamiliar with the older style updraft carbs that we have. In a downdraft carb, there is no need for a scavenge tube.

[Dave Neptune]

Not that bad

Richie, welcome to ur: world. For some reason "mechanics" who "think" they're good are more interested in fixing or selling you a diesel. A real mechanic of which there are few of left can work on diesels and these old engines which are far simpler. One of the biggest problems leading to their dislike is that most A-4;s are in tight quarters in small boats that they were DESIGNED for. Mine has been running for 43 years now~and I say that ain't to shabby.

Get yourself a carb kit and before breaking the carb apart read the directions! There are many good rebuild explanations on other threads, take a look. Get a pic or 2 as well of the installation and give us a basic description of your fuel system from the tank. When you pull the fuel line off the carb be sure to have a plug ready, an unused "nozzle" from a silicone tube works great and it will "fit" into almost any size you'd find on an A-4. Pulling the carb and old fuel lines will often CAUSE problems and replacing the fuel lines is cheap and just a good idea every 5 years or so anyway.

There are a few tricks to separating the carb, being careful to get the venturi loose so you don't bend the floats while splitting the gasket.

Dave Neptune

[roadnsky]

Richie-
First, the boys are correct...
DON'T get rid of the scavenge tube.
That one instance of BAD advice should be enough incentive to get you inspired to work on the A4 yourself and not trust her to others.
Stay here and ask questions. Get the MMI A4 Manual and go to it.
Trust us. You can do it!

A couple of questions...
Can you describe how MUCH of a fuel leak you have?
Are we talking about a small drip or a steady stream of fuel?
Does it only leak while the engine (and fuel pump) are running?

This could be as simple as just needing to snug up the tube fitting to the bottom of the carb bowl.

[Richie740]

Thanks guys!

The leak was a pretty consistent drip drip every second or two without the engine running. Once I finally secured the petcock valve it slowed down considerably but still existed (even after I drained the carb bowl & replaced water separator inline before fuel pump).

The drip was definitely coming from scavenger tube at the bottom of the carb as in the picture above but I'm not 100% confident that's the source of the leak.

[sastanley]

rich,
You are right not to assume the source of the leak is the tube itself...since it is at the bottom of the carb, any fuel leaking out of the carb from anywhere could, and likely will, end up at the lowest point, the tube orifice, on its way down, and give the scanvenge tube the appearance of a leak.

If the boat doesn't already have one, I highly recommend the Moyer Service Manual & at least a few gaskets...a flange gasket where it connects to the manifold, & the bowl gasket so you can re-assemble the carb after cleaning. This should be your first order from Ken in the Moyer parts department.

Also, make sure to pick up some Permatex from your local auto boutique, or the hard-to-find nearby Wal-mart. There are several different kinds...Don Moyer highly recommends the #3 "Aviation Brand" which is in a white jar with a brush. We slather that stuff on most threaded connections (i.e. the brown stuff in Jerry's pic) to help seal the threads, and also often on gasket connections to aid the gasket. I wouldn't use it on the carb bowl gasket, but I would on most others...t-stat, side plate, valve cover, water pump, etc., because you will eventually have all those parts off.. Others like the #2 Permatex in a tube..slightly less runny. I also recently found some "high tack" Permatex, also in a jar and works similar to the #3.

I keep a jar at home and on the boat in case I grab an engine part and bring it home for work on the bench.

P.S.> I would not let that boatyard guy within 50 yards of my boat.

[romantic comedy]

That boat yard guy sounds like he knows, either the Atomic Four, or up draft carbs, at least. He gave poor advice, but obviously knows a thing or two.

When you work on the charging system, the accept wisdom, is to start with a good fully charged battery. I think the same applies to the fuel system. You need to have a good clean functioning carb. This carb is quite simple, and easy to rebuild.

There is a lot of resources material here, so just do it. I know that you can!!

[CalebD]

My 45 year old Atomic 4 has made something of a mechanic out of me. When I first met my Atomic 4 I had no idea that it had a water pump with a grease cap fitting. Now I can pop the carb off the engine in about 2 minutes.

Tools/materials you will need:
-socket wrench set
-white oil absorbent pads (for fuel as well)
-MMI A4 manual
-Permatex gasket goop
-spare gaskets
-(optional) gloves or hand degreaser
-(recommended) crappy work clothes so you can look like Bogey in the "African Queen".

[Al Schober]

OK, my $.02
The scavenge tube was common on early engines. Later engines did away with it. USCG regulations regarding.. no idea. My engine doesn't have one. But handy to have if your carb overflows and you get fuel in the throat. But a leak in the scavenge tube is not the problem that needs fixing.
If you're getting fuel in the throat, it's overflowing from the carb. I'd suspect that your float valve isn't working, possibly because a) you need a new needle/seat, or b) the float isn't floating. Address these issues and your problem will go away.

[romantic comedy]

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

I had not heard that before.

[tenders]

Mine is one of the last ones made (casting date 02/25/80) and has the tube.