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  #1   IP: 207.55.29.114
Old 04-19-2012, 11:21 PM
Mart Mart is offline
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Technicial Question on fuel system tubing

All,

I have a question on the reliability of the two types of copper tube fittings? These are the flair and compression joins.

I am in the process of familiarizing my self with the Zenith 86 carburetor. I was able to find the back ground information on the scavenge tube on the list. Part of my process is to build a emergency parts kit so that should I have to make repairs the need parts could be are on board. The scavenge tube is a uncommon item as it is a 1/8th inch tube. I was able to find that dimension of tube and brass fittings. What I have not found is a 1/8th flare vice and tool. My old vice's smallest dimension is 5/16th. Checking with some of the better hardware stores in the area I was unable to locate the needed tools.

I have greater trust in the flare joint system. It appears that I could assemble the scavenge tube with compression fittings.

Does any one a an opinion or knowledge on which joint is the most reliable? Yes, I could buy the part from Moyer Marine. The effort here is take responsibility for my boat's performance and reliability and to learn how to make repairs and under take maintenance. Any thoughts on this is most welcome.

Thank you,

Mart
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  #2   IP: 76.189.1.205
Old 04-20-2012, 12:30 AM
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I believe gas line fittings are REQUIRED to be flare fittings and compression fittings are not permitted. I don't know if the scavenger tube would count as a gas line, since it's not pressurized at all, but a leak would be bad, and this is one place where I'd buy the part to do it right rather than take a chance.
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  #3   IP: 173.11.96.181
Old 04-20-2012, 08:10 AM
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When I rebuilt my engine and was re-installing the scavenge tube, I could not find flared fittings in the tiny 1/8" size, but I did find compression fittings. I have not had a problem yet. Lots of plumbing jobs use compression fittings (every supply line under your sink or toilet, as well as your refrigerator's icemaker supply line). As long as it's done correctly (a rule that applies equally to a flared fitting), I don't see why it should be a concern.

Someone will be along shortly to correct me if I'm totally mistaken here.
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  #4   IP: 184.0.176.66
Old 04-20-2012, 08:19 AM
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Question

This may be a question for Neil's CFR library.
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  #5   IP: 24.152.131.155
Old 04-20-2012, 08:53 AM
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I dug through the CFR's on fuel systems. There's a discussion of scavenge tube requirement for updraft carburetors but nothing specific on the required material. It's therefore reasonable to apply the general requirements for tank to engine fuel line requirements to the scavenge tube because it handles fuel.
Quote:
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.

Marine engines today use downdraft carburetors; however, if an engine uses an updraft or a horizontal draft carburetor, then it must be fitted with a means to collect fuel from flooding and return it to the engine so it will be consumed. Some auxiliary generators and some small propulsion engines have updraft or horizontal draft carburetors.
The collector for the fuel must be capable of holding or delivering to the engine a quantity of fuel that collects during 12 ten-second periods of cranking without external leakage from the air inlet or dripping of liquid fuel from joints in the air inlet components. The collector and carburetor must be designed so that fuel will run into the collector rapidly to prevent fuel collection in the carburetor horn where it can be expelled during a backfire or "spit-back."
The collector must be fitted with a stripping means to return the collected fuel to the engine for combustion. Typically, this stripper is a tube connected to the throat of the carburetor so the manifold vacuum will pull the fuel out of the collector.
As for metallic fuel lines, there is no discussion on termination types. There are however, requirements for the line itself:
Quote:
183.538 - Metallic fuel line materials
Each metallic fuel line connecting the fuel tank with the fuel inlet connection on the engine must:
(a) be made of seamless annealed copper, nickel copper, or copper nickel; and
(b) except for corrugated flexible fuel line, have a minimum wall thickness of 0.029 inches.

If metal is used for any portion of the fuel line (except for fittings) from the tank connection to the engine connection (usually at the fuel pump), the metallic fuel line portions must be seamless, annealed:
(1) Copper;
(2) Nickel copper (Monel); or
(3) Copper-nickel.
No other metals are permitted.
Also, the thickness of the tubing wall must be at least 0.029 inches unless the fuel line portion is a corrugated or accordion type of flexible fuel line. Tubing is available with thinner wall thicknesses, but they SHALL NOT be used.
Metal fuel lines used on the engine, i.e. the fuel line from the fuel pump to the carburetor, may be made of materials other than those listed. This line is usually supplied with the engine.
BTW, I checked my flare tool, it goes down to 3/16". Close but no cigar.
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Last edited by ndutton; 04-20-2012 at 08:57 AM.
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Old 04-20-2012, 06:47 PM
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Good News and Bad News

First the disclaimer: I used compression fittings in my motor rebuild.

However: 1/8" flair tools are pretty easy to find from industrial supply places like McMaster-Carr

McMasterCarr Flair tool catalog page

BUT they are not cheap--something over $100 for the cheapest. If you call around to some specialty plumbing, machine shops or the like you might be able to find someone to flair your tube for cheap. On the other hand, by time you pay for your gas and consider your travel time it might not cost anymore to include it with your next Moyer Marine order.
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Old 04-21-2012, 12:09 PM
Mart Mart is offline
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All,

Very informative discussion. As a result, I have two additional questions. The first regards the material of the fuel line. Clearly, the fuel lines are required to be copper or Monel or copper-nickle if they are composed of metal. Given the occurrence of SAE fuel hose am I safe to assume that is considered safe and legal?

The second question, CFR am I correct that this is a Coast Guard safety code published in the Consolidated Federal Register?
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Old 04-21-2012, 12:44 PM
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Quote:
Given the occurrence of SAE fuel hose am I safe to assume that is considered safe and legal?
Yes. With the ethanol component in gasoline be sure to use 'Type A1', rated for alcohol. I prefer hose, much more tolerant of vibration. In fact, metallic fuel lines affixed to the boat's structure are required to have a flexible section before connecting to the engine.

Quote:
CFR am I correct that this is a Coast Guard safety code published in the Consolidated Federal Register?
Yes and no.
Yes, it's the USCG standard.
No, not the Consolidated Federal Register but close, it's the Code of Federal Regulations.

For our purposes here I keep them close at hand. The articles regarding inboard gasoline engines, fuel systems, ventilation, exhaust systems and electrical seem to me to be a good reference and often times bring us back on track.

Despite the wealth of experience on this forum, sometimes what is presented is contrary to the regs. For example, exhaust hot section material is frequently discussed, usually after a picture of a new galvanized system is posted. It will go back and forth with one member thinking this, another that and then we'll quote the USCG Regulation (actually the ABYC recommendation adopted into regulation by the Coasties). That usually settles the issue until the next time.
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Old 04-23-2012, 05:43 AM
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next time

...and there is always a next time!
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