1955 Johnson 5.5 hp, pressure tank conversion, troubleshooting

Walston

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May 31, 2010
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Last year we bought this Johnson and fixed it up. It was in quite good shape and has not been used much over the years. We installed new coils, rebuilt the carbs and put a new impeller in it. It truly runs like new, starts first pull every time. Still has original pressurized tank. We had the boat out a few times this year, ran great every time.

So my son and I wanted to install a fuel pump and get away from the pressurized tank, mainly to satisfy Mom/Wife. I followed this websites procedure. http://www.outboard-boat-motor-repai...on/default.htm

Got a Mukini fuel pump. Removed the flapper valve under the intake manifold and plugged one side using a vacuum hose cap. Bought a new 3 gallon tank. Bought a new fuel line, with squeeze ball. Installed everything.

The motor ran decent in the barrel, but seemed to struggle going from full throttle to idle and it stalled several times. Was hard to start. But we worked with it and we seemed to have it running decent, so we took it to the lake today. Very disappointing.

Engine would start after a few pulls and idled OK, at full throttle it seemed to have less power and seemed to be fuel starved and would stall after a minute or so, we would have to pump with the squeeze ball to keep the engine going. i.e. we were supplementing the new fuel pump. The tank was vented. We actually tried not venting to see if it helped, didn't seem to make a difference, I assume it should be vented.

We pulled the line from the inlet to the fuel pump off (coming from the new tank and purged any air to be sure. No help.

With the engine running we removed the hose that is supposed to provide the "pulse" to the fuel pump and it seemed to be doing that. I am stumped.

I have decided to order a new "screen filter" that is in the carb, it is the only thing else I can think of, maybe the fuel pump is a slightly lower pressure and the filter is too clogged for the pump even know it works fine for the pressurized tank???

You guys have any suggestions?
 

F_R

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Jul 7, 2006
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28,195
Re: 1955 Johnson 5.5 hp, pressure tank conversion, troubleshooting

The filter is a good guess and a place to start. If that isn't it, get your hands on a fuel pressure gauge and T it into the line between the pump and carburetor. It should maintain 2-4 psi while running. Harbor Freight has the gauge, cheap. Actually, they are a combination vacuum/fuel pressure gauge.
 

Walston

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May 31, 2010
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Re: 1955 Johnson 5.5 hp, pressure tank conversion, troubleshooting

While I wait for the "screen Filter" for the carb to be delivered, I cleaned the old filter with cab cleaner and MEK. I also installed a pressure gauge between the Mukuni fuel pump and carb. Starts fine and runs, at idle there a is a pulsing pressure of 4 to 8 psi, about what you would expect. However, when I increase the engine speed the pressure drops to zero and the engine eventually stalls due to lack of fuel. It seems like it will run all day at idle. I am starting to suspect that our plug inside the intake manifold is leaking.

Any thoughts or ideas?
 

1946Zephyr

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Oct 21, 2008
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Re: 1955 Johnson 5.5 hp, pressure tank conversion, troubleshooting

Oddly enough, the Mikuni users found that it's okay to use that connection for a fuel pump actuator. Myself, I always though it best to work off of the intake ports, like factory fuel pumps are mounted. The higher the rpms go, the greater the pressure you get, unlike loosing air pressure like you are now.
 

Walston

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Re: 1955 Johnson 5.5 hp, pressure tank conversion, troubleshooting

Oddly enough, the Mikuni users found that it's okay to use that connection for a fuel pump actuator. Myself, I always though it best to work off of the intake ports, like factory fuel pumps are mounted. The higher the rpms go, the greater the pressure you get, unlike loosing air pressure like you are now.

Thanks. Can you tell me a little more about how I would do that?
 

jmendoza

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Jun 9, 2008
Messages
314
Re: 1955 Johnson 5.5 hp, pressure tank conversion, troubleshooting

Sounds like you are losing crankcase pressure: I would suspect your manifold or that hose cap is leaking. One thing it could also be is a seal, but before you go any further, did you replace the hose that connects the upper and lower bearings together? If that hose has a leak, both cylinder one and two will have case leaks. I had to replace it on my 1954 CD-11. I used the square Mikuni pump, works great.
 

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Walston

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Re: 1955 Johnson 5.5 hp, pressure tank conversion, troubleshooting

Sounds like you are losing crankcase pressure: I would suspect your manifold or that hose cap is leaking. One thing it could also be is a seal, but before you go any further, did you replace the hose that connects the upper and lower bearings together? If that hose has a leak, both cylinder one and two will have case leaks. I had to replace it on my 1954 CD-11. I used the square Mikuni pump, works great.

I will certainly check that, I did not replace that hose and it looks easy to do. Thanks. Nice looking Johnson, ours could be a twin.
 

Walston

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Re: 1955 Johnson 5.5 hp, pressure tank conversion, troubleshooting

UPDATE:
So I replaced the external hose that goes to the bearings, just in case it was leaking, and that didn't help. The hose didn't appear to be bad, but I thought it was worth a shot. So I went to Harbor Freight and bought an actual fuel pressure/vacuum gauge and installed in the the line between the pump and the carb. I just wasn't getting pressure. It was just below 1 psi at idle and went to zero when I sped up the engine. Once on zero, the engine would run a few more seconds and stall. So I was now convinced that it was either the the pump or the plug under the intake manifold. The pump is new, so I took the carb and intake manifold off again and replugged the hole with a tighter fitting vacuum cap, put it all back together and now I have between 3 and 4 psi pump pressure and the motor runs quite well in a tank. I think we are ready to try it on the lake again. I think the results will be much better this time.

Thanks for the ideas.
 

AlTn

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Mar 9, 2010
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Re: 1955 Johnson 5.5 hp, pressure tank conversion, troubleshooting

Thanks for posting the solution
 

VIMike

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Sep 1, 2011
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Re: 1955 Johnson 5.5 hp, pressure tank conversion, troubleshooting

I am glad you asked this question because I am looking at a '63' 5.5 Evinrude that doesn't have a tank or hose to test it. Now before I buy it I have heard from all my local vendors that the old pressurized hoses and tanks can't be found. Since I am not that mechanical I would prefer just buying them. Do you have access to these in your neck of the woods?
ps I have read the Aug3rd 2010 thread of converting the 1957 5.5 Evinrude.
 

Chinewalker

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Aug 19, 2001
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Re: 1955 Johnson 5.5 hp, pressure tank conversion, troubleshooting

A 1963 is already a fuel pump motor - no pressure tank to worry about...
 

kfa4303

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Sep 17, 2010
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6,094
Re: 1955 Johnson 5.5 hp, pressure tank conversion, troubleshooting

Hi VIMike. Welcome to iboats. Chinewalker is right. If you're going to get a '63 5.5 hp, it will already have a fuel pump and can use a regular/modern OMC fuel line. It will use a 24:1 mix too. That's about 5.5 oz. of oil to 1 gal of gas. I usually just round up to 6 oz. You can get the oil, fuel lines and tank at Wal mart or any marine supply store. Here are some handy links for your (almost) new toy.

http://www.outboard-boat-motor-repa...hnson 5.5 HP 1954-1964 Carburetor Tune-UP.htm
http://forums.iboats.com/showthread.php?t=158086
http://www.duckworksmagazine.com/07/columns/max/index1.htm
http://forums.iboats.com/showthread.php?t=167352
 
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