1958 Evenrude 7.5 HP Fleetwin-dual line gas feed system not functioning

[Rick_Wms]

Need some help on fixing this motor. Really the issue is the gas tank/hoses/fittings fuel feed system
History: This motor was given to me. Probably has 10 to 15 hours on it. When I got it I cleaned out the carb and flushed the fuel system as best I could and tried to start the engine. No go. I read up on this dual line fuel system (fuel + air) which was new to me. Will save you all the details but eventually developed a gravity feed fuel system (with a funnel + hose right to the fuel bowl). Bang, the engine started right up. I kept feeding the funnel with gas to keep the engine running so I could adjust the high and low rpms fuel mixture. As long as I kept feeding the funnel the engine ran. Next I purchased a gas can gasket rebuild set and rebuilt the gas can (diaphragm et al). Filled the gas tank but the gas will not prime to the fuel bowl. I can see in the fuel bowl on the motor the gas level move because air pulses the level when I push the gas can plunger. I even feel a light pressure air (depress the ball in the fuel line at the connection to the motor) when I pump the plunger on the gas can - but no fuel up to the bowl. I primed the gas line with gas reconnected the gas hose from the tank directly to the fuel bowl, pumped the plunger, engine would run a minute or two and die. Believe the engine ran on the gas in the fuel bowl only. In all cases I had the air hose return hooked up to the engine. So a bunch of questions for those smarter than me.
1) not getting a prime from the gas tank - what can I check to see all is well with the diaphragm in the tank using the plunger, suppose to be new and functional from the rebuild kit
2) how do I check that I am getting positive pressure from the intake to the gas can that is part of this crazy fuel system
3) can I change out the o rings and spring in the connection of the air/gas line to the motor?
4) how can I test all the above to make sure they are working correctly
5) is there a way to adapt a current version of a fuel pump so I could go to the more current single gas line feeder system?

[Joe Reeves]

The cap on the pressure tank must be tight. The plunger must be pressed until it is hard (carbs etc full) with the fuel connector attached to the engine. Even when all is well, it takes a few false starts to get pressurized air into the tank unless it is absolutely full. You don't say how long this engine has been sitting.... how long?

1 - If no fuel is being pumped from the tank when you're pressing the plunger, you'll need to dismantle the tank to find out why
2 - Air pressure from the engine?... You'll need to disconnect the air hose when the engine's running.
3 - The "O" Rings can be replaced... no need to replace the springs unless they're broke.
4 - That's up to you... check that gas flows when you pump the plunger etc.
5 - Some engines can be converted to a fuel pump... some can't. Some other member will need to answer that question.

Bottom line.... If by carefully depressing the bra$$ fuel valve in the fuel connector and pumping the tank plunger, no fuel is pumped out the connector, dis***embly of the tank is a must to find the cause.

[Rick_Wms]

Thanks Joe. The engine has been sitting for years before i got it.
The gas cap has been tight when I have done all my engine starting attempts. The tank plunger only has a 1/2" throw. so don't know if that is typical. I have noticed that the plunger feels soft and not hard as people have described. This combined with (depressing the br*** fuel ball in the connector) with no gas flow points to the tank/hose/connectors issues. So will tear into the tank again to check what is going on there.
Next, I will get the engine running with my adhoc gravity fuel feed to feel if there is pressure coming off the engine in the air return line to the tank. There is suppose to be return air pressure in the hose - correct? Isn't this how the tank gets pressurized? if not what is the reason for the dual line that says "air"?
For those that know if I can convert to fuel pump system on the motor, here is the engine id: 1958 Fleetwin 7.5 hp serial 7524-07250

[Joe Reeves]

The 1/2" travel of the fuel tank plunger sounds about right drawing on memory... yeah, I worked on those things back then when a person could buy a new one. Yes, the engine pumps air to the fuel tank to pressurize the tank in order to force fuel to the engine.