dual fuel line pressurized tank 1955 evinrude 25 hp

[evinrude25018]

Does the crankcase pressure need to be reduced before pressurizing the the tank? Should I convert to a single line? If I should convert can you recommend a fuel pump, or other method to do so? Thanks!

 

[jimmbo]

Crankcase pressure is what pressurizes the tank. The button doesn't pressurize it, it pumps fuel to the carb to fill the carb. It is possible to convert it to a single hose system. I pre 1984 style fuel pump can be mounted on one of the bypass covers, or a fitting for a pulse hose can be mounted there for a remote fuel pump. Check the iboat store for complete replacement pumps for the 25 - 40 hp engine from the late 60s and early 70s

 

[82rude]

Is there something wrong with your setup or have you been caught up in the unfounded non-sense that 2 line tanks are bad ,dangerous etc.The actual pressure is about 3 lbs psi or so.I have a few 2 liners and they still work perfectly and have never been touched.If you want to change to 1 line for the ability to use a larger tank or a larger plastic tank fine but theres no need to be fearful of the old style .There were lots of old wives tales about them all unfounded and total nonsense.The main reason omc went to 1 line was cost related .

 

[F_R]

Does the crankcase pressure need to be reduced before pressurizing the the tank? Should I convert to a single line? If I should convert can you recommend a fuel pump, or other method to do so? Thanks!

No, the crankcase pressure does not need to be reduced. It goes directly to the tank at whatever the peak pressure is, usually around 4 psi. A pressure relief valve within the tank vents air if pressure should happen to get too high (such as sitting in the hot sun).

 

[racerone]

I agree with post # 4.-----Just so much nonsense and mis-understanding on a simple reliable concept.

 

[Scott Danforth]

welcome aboard.

nothing wrong with a 2-line tank unless the tank is all rusty and leaking

 

[jimmbo]

The main reason for the pressurized systems demise was there were few, if any tanks, other than the 6 gallon ones . Larger built in tanks weren't offered by the engine manufacturers, and I can't ever recall 3 party tank makers willing to build them. There was the safety issue of them springing a leak under pressure. But those tanks were made of thicker steel than the single line tanks. Maybe that's why the 3rd party manufacturers didn't want to make them, higher cost, and maybe the higher risk of liability.

 

[racerone]

I would rather run with a pressure tank than some of the plastic junk marketed today.

 

[F_R]

I would rather run with a pressure tank than some of the plastic junk marketed today.

Amen to that.

 

[evinrude25018]

Thanks everyone. I have the motor but no tank so I was wondering if I'd be better off switching to a diaphragm pump or similar with a single line or if I should seek out/make a 2 line pressure tank. Sounds like the pressure tank is the simplest way to go..

 

[Crosbyman]

not being to nostalgic I have converted several motors from the 5.5 to 15 hp range and all work great .

Pump on the bypass cover was the simplest way versus using the air pressure nipple behind the carb and sealing one channel (see UTUBE OMC CONVERSION)
https://www.youtube.com/watch?v=FtG4M7ye1N8
Some plastic tanks are thin ,worrisome and cheap but some are real sturdy and pricier like the Mercury plastic tanks

lots of metal ones if plastic is not your thing .

 

[F_R]

Thanks everyone. I have the motor but no tank so I was wondering if I'd be better off switching to a diaphragm pump or similar with a single line or if I should seek out/make a 2 line pressure tank. Sounds like the pressure tank is the simplest way to go..

Well, IF you already have a good pressure tank, that would be the simplest and cheapest way to go. But another story if you have to buy one. In that case, the conversion makes more sense. Especially if you live in a part of the country where used pressure tanks are rare as chicken fangs and if you do find one it probably is full of rotted gas and rust.

BTW, as for originality, OMC offered an accessory conversion kit back in "The Day". Gale motors already had the pump.

 

[evinrude25018]

No, the crankcase pressure does not need to be reduced. It goes directly to the tank at whatever the peak pressure is, usually around 4 psi. A pressure relief valve within the tank vents air if pressure should happen to get too high (such as sitting in the hot sun).

So I tried this with no release valve and flooded it, so I will get a release valve as you mentioned and see what happens. I bought a new tank and tapped a pressure port into it.

 

[evinrude25018]

No, the crankcase pressure does not need to be reduced. It goes directly to the tank at whatever the peak pressure is, usually around 4 psi. A pressure relief valve within the tank vents air if pressure should happen to get too high (such as sitting in the hot sun).

It seems like there is an additional check valve needed on the tank. Also I have clear fuel line and I can see voids develop when it runs for a brief minute before dying.
Can see the diaphragm here
https://www.maxrules.com/fixomcmovers.php
https://www.maxrules.com/graphics/omc/p-tank-old.jpg
I guess maybe that was obvious to others, not me,I've never worked on a 2 stroke outboard before

 

[F_R]

There are two check valves in the tank. One is item #25 in the above drawing, and the other is inside the pickup tube assy #41. Neither one does anything once the motor is primed and running. Well, I take that back. The one in the pickup tube often gets stuck shut from old rotten gas gum.

 

[oldboat1]

I can't quite figure out what you are doing. Did you find a pressure tank? They can be had -- $40 or $50 for a working one would be about right (imo). $150 is out of bounds. Try the AOMCI free webvertise, or attend a meet in your area.