​1958 Johnson Seahorse 18hp air pressure issues

dwittig33

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Hey there, i got a motor i have been working on for a while. Finally got it to run a bit and it dies once the carb runs out of fuel. It does run if i set the tank above the motor or if i press the primer button (two line fuel line btw). I have rebuilt the carb and the tank and can't find any air leaks in the lines either. The tank seems absolutely solid because when i prime it the button gets super stiff. What's next? Take a look at the check valves coming out of the crankcase? Appreciate your help.
 

gm280

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If I'm understand correctly, your engine doesn't have a fuel pump but pressurizes the fuel tank for fuel delivery. If that is the situation, then your tank has a leak in it somewhere and therefore not pressurizing correctly. Check the fuel line(S) and primer bulb to make absolutely sure they are not cracked or leaking as well. The fact that when you set the tank higher then the carb gravity takes over and the fuel flows to the carb. So you are lacking pressure... JMHO!
 

F_R

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Agreed, it would appear it isn't pressurizing. The quick test is to loosen the cap after it runs a few minutes. You should get that wonderful hiss as air escapes. If not, you will have to find the leak. Tank, hose, connector, or pressure valves in the motor. We can guess but you still have to do the search. Think looking for bubbles in soapy water.
 

nwcove

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the primer button only pumps fuel to the carb, it does not pressurize the tank.
 

boobie

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Take a look at the check valves in the intake manifold. AKA, the " Minnie Mouse" bra.
 
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dwittig33

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Yeah I'm going to take a look at the check valves. I just can't find any air leaks in the lines. Does anybody know what size fuel line that is on that motor? I need to get some anyways. Thanks
 

hardwater fisherman

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OMC part number 0772566 sold by the foot. Sierra part number 18-8051 sold here at iboats. According to a seller on ebay they are both 1/8 inside diameter.
 

F_R

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So....yes it is possible it may be the check valves. Also probably not the problem. Personally, I'd try pressurizing the tank with compressed air first to see if it holds air. Just my 2c.

Another thing: Have the fuel air hoses been removed at either end? Swap them onto the wrong nipples and it won't work. Note one hose has a ridge along the side for I.D. Air must go to air and fuel to fuel on the connector and tank.
 

gm280

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Well If push comes to shove, you could always change it all over to a fuel pump (electric or tap into the manifold and use the pulse system) and go to a regular tank and forget all about the pressurized system. I'm sure others have successfully done that before... JMHO!
 

racerone

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When the motor is running on the carburetor full of fuel you can remove the connecter.---Does air come out the airline from the motor at the fitting ?-------The pressure tanks are very simple and very reliable.
 

dwittig33

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Found the problem. There's a drain hole in the tank that is open and letting all my air out. Not the vent in the cap but a hole labeled drain. I see it's not threaded or anything so I'll just have to jam something in
 

racerone

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Are you sure it is not threaded ?----Just a screw missing ?---Can you see if one of the other screws will fit in that hole ?
 

F_R

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Should be threads in there, down a way in the hole.
 

dwittig33

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why is it so difficult to upload pictures here? it says only 200,000 bytes is the limit which is nothing. anyways trying to upload a picture of it to make sure we are talking about the same thing.
 

dwittig33

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and why do they have a drain there? maybe that was used to vent the tank before the caps had vents in them?
 

racerone

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One of the screws was removed so that all the fuel could be drained !!!---------The cap is closed when motor is running.----Fuel can not be fully drained by just taking the cap off.------Me thinks someone lost the screw and gasket.---Sorry, but that is the way it was designed in the early 1950's and elegantly simple too.
 

dwittig33

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Oh to drain the fuel out of the line and the guts of the tank. That makes sense. Well motor is running good now finally. Thanks for your help
 
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