Replacement Fuel Line Size - Moderated Discussion Areas

  ContinuousWave
  Whaler
  Moderated Discussion Areas
  ContinuousWave: Whaler Repairs/Mods
  Replacement Fuel Line Size

search | FAQ | profile | register | author help

Author Topic:   Replacement Fuel Line Size

jason78 posted 12-23-2013 11:06 AM ET (US)
Hello. I am replacing the tank fuel hose and water separating filter housing on my 1998 20 Outrage with a 200-HP Offshore outboard engine with carburetors. I have already purchased a replacement water-fuel separting filter housing. A few months ago, my mechanic replaced the fuel hose running from the water-fuel separating filter to the outboard engine with a Mercury 5/16-inch lineset. After removing the old housing, it appears the original was outfitted with 3/8-inch barbed hose fittings on inlet and outlet rather than 5/16-inch. At this point I can't tell if the hose form tank to filter is 3/8-inch or 5/16-inch, but I need to replace that as well.
Is there any compelling reason to use 3/8-inch instead of 5/16-inch from fuel tank to filter? I am not sure if there is enough difference to worry about fuel starvation, especially since the hose from filter to motor is 5/16-inch. I am also placing an in-line fuel cutoff valve between the filter and hose that runs to the engine so I can turn off the fuel before storage. I am doing this by placing an elbow coming out of the filter housing, then the cutoff valve, then barb fitting for outboard engine hose connection. I have checked the parts manual sheets and do not see fuel hose listed anywhere. I am using all 1/4-inch brass fittings. Thanks Jason
jimh posted 12-23-2013 01:27 PM ET (US)
Typically the fuel flow rate of a carburetor outboard engine of 200-HP would require the fuel hose and fittings in the line to be 3/8-inch diameter. If you plan to replace existing hoses and fittings, I would use 3/8-inch ID hose and appropriate fittings, rather than use 5/16-inch. From your narrative, it sounds like you have a mix of two sizes now.
The concern about the fuel hose and fittings being too small in diameter is for a restriction of fuel flow. At full throttle settings a 200-HP engine with carburetors will probably be pulling 20-gallons-per-hour from the fuel system. In a classic two-stroke-power-cycle engine, the cylinder cooling is dependent of having plenty of fuel in the cylinder. If a cylinder runs lean, the cylinder temperature will be higher. High cylinder temperature leads to problems. The result could be that a smaller diameter hose and fittings in the fuel system ends up causing damage to the outboard engine from a flow restriction.
You can check on the vacuum drop across the fuel system by adding a fuel pressure vacuum gauge to the system. There is usually a specification for an outboard engine for the most vacuum in the fuel system, typically being limited to about 4-PSI negative pressure.
tmann45 posted 12-23-2013 07:15 PM ET (US)

quote:
Is there any compelling reason to use 3/8-inch instead of 5/16-inch from fuel tank to filter? I am not sure if there is enough difference to worry about fuel starvation

Yes there is, 3/8" ID hose is 44% larger than 5/16" ID hose when you look at volume and flow rate.
jason78 posted 12-23-2013 10:37 PM ET (US)
OK, thanks for the help! I found the parts manual and it looks like I need Mercury p/n 17146A8 which appears to be superseded by 32-877681Q8. An 8 foot fuel hose assembly with quick disconnect on one end. Nowhere I have found so far lists the ID size of the actual hose used in this p/n. Maybe I will need to call Merc to confirm it is 3/8"? Unless someone here knows?
Next back to the fuel cutoff switch; based on the placement of the remote water sep filter housing, I would need to do an elbow out of the filter housing, attach the fuel shutoff valve, then the hose barb to the shutoff valve. I have read in some places that 90 degree elbows are a no-no in fuel lines. What is the consensus here on that? Anyone done this?
Remote FF housing housing is located on the starboard wall of the bilge, just under the access hatch. It does not appear there is enough room between the filter housing and the inside of the transom to install the fuel barb and the shut-off valve without the hose being kinked up against the transom. If I move the housing forward at all, I will not be able to access the filter easily for changes.
Thanks
Jason


Hop to:

Contact Us | RETURN to ContinuousWave Top Page

Powered by: Ultimate Bulletin Board, Freeware Version 2000
Purchase our Licensed Version- which adds many more features!
© Infopop Corporation (formerly Madrona Park, Inc.), 1998 - 2000.

Author	Topic: Replacement Fuel Line Size
jason78	posted 12-23-2013 11:06 AM ET (US) Hello. I am replacing the tank fuel hose and water separating filter housing on my 1998 20 Outrage with a 200-HP Offshore outboard engine with carburetors. I have already purchased a replacement water-fuel separting filter housing. A few months ago, my mechanic replaced the fuel hose running from the water-fuel separating filter to the outboard engine with a Mercury 5/16-inch lineset. After removing the old housing, it appears the original was outfitted with 3/8-inch barbed hose fittings on inlet and outlet rather than 5/16-inch. At this point I can't tell if the hose form tank to filter is 3/8-inch or 5/16-inch, but I need to replace that as well. Is there any compelling reason to use 3/8-inch instead of 5/16-inch from fuel tank to filter? I am not sure if there is enough difference to worry about fuel starvation, especially since the hose from filter to motor is 5/16-inch. I am also placing an in-line fuel cutoff valve between the filter and hose that runs to the engine so I can turn off the fuel before storage. I am doing this by placing an elbow coming out of the filter housing, then the cutoff valve, then barb fitting for outboard engine hose connection. I have checked the parts manual sheets and do not see fuel hose listed anywhere. I am using all 1/4-inch brass fittings. Thanks Jason
jimh	posted 12-23-2013 01:27 PM ET (US) Typically the fuel flow rate of a carburetor outboard engine of 200-HP would require the fuel hose and fittings in the line to be 3/8-inch diameter. If you plan to replace existing hoses and fittings, I would use 3/8-inch ID hose and appropriate fittings, rather than use 5/16-inch. From your narrative, it sounds like you have a mix of two sizes now. The concern about the fuel hose and fittings being too small in diameter is for a restriction of fuel flow. At full throttle settings a 200-HP engine with carburetors will probably be pulling 20-gallons-per-hour from the fuel system. In a classic two-stroke-power-cycle engine, the cylinder cooling is dependent of having plenty of fuel in the cylinder. If a cylinder runs lean, the cylinder temperature will be higher. High cylinder temperature leads to problems. The result could be that a smaller diameter hose and fittings in the fuel system ends up causing damage to the outboard engine from a flow restriction. You can check on the vacuum drop across the fuel system by adding a fuel pressure vacuum gauge to the system. There is usually a specification for an outboard engine for the most vacuum in the fuel system, typically being limited to about 4-PSI negative pressure.
tmann45	posted 12-23-2013 07:15 PM ET (US) quote: Is there any compelling reason to use 3/8-inch instead of 5/16-inch from fuel tank to filter? I am not sure if there is enough difference to worry about fuel starvation Yes there is, 3/8" ID hose is 44% larger than 5/16" ID hose when you look at volume and flow rate.
jason78	posted 12-23-2013 10:37 PM ET (US) OK, thanks for the help! I found the parts manual and it looks like I need Mercury p/n 17146A8 which appears to be superseded by 32-877681Q8. An 8 foot fuel hose assembly with quick disconnect on one end. Nowhere I have found so far lists the ID size of the actual hose used in this p/n. Maybe I will need to call Merc to confirm it is 3/8"? Unless someone here knows? Next back to the fuel cutoff switch; based on the placement of the remote water sep filter housing, I would need to do an elbow out of the filter housing, attach the fuel shutoff valve, then the hose barb to the shutoff valve. I have read in some places that 90 degree elbows are a no-no in fuel lines. What is the consensus here on that? Anyone done this? Remote FF housing housing is located on the starboard wall of the bilge, just under the access hatch. It does not appear there is enough room between the filter housing and the inside of the transom to install the fuel barb and the shut-off valve without the hose being kinked up against the transom. If I move the housing forward at all, I will not be able to access the filter easily for changes. Thanks Jason