old evinrude 7.5 outboard

hi i own an older model evenrude 7.5 and i am having problems with the gas tank i think its not getting gas from the tank . i understand that the tank is pressurized because the motor has no fuel pump ,how difficult would it be to obtain a new tank and hose assembly and or to add a fuel pump to the motor itsself? please help serial # 7520 05531 perhaps a guess at the year of this model?

I would suspect the fuel is gravity flow from the tank to the carburetor. If so you might want to check the air vent in the gas tank cap, could possibly be plugged. I had that happen with a Briggs and Stratton roto-tiller engine. The engine would start and run for up to a minute and then die. It would start again and then die. It was creating a vacuum in the tank and the gas would cease to flow. As soon as I replaced the gas cap it worked as normal. - just a thought.

You did not state the year of the engine which leads to some assumptions. Older outboards with the gas tank on the engine were gravity feed.

Later on, to use a remote tank, the manufacturers installed a small check valve in the crankcase to bleed off a little crankcase pressure. These little pulses of crankcase pressure were fed to the remote tank through a rubber hose, usually to a 6 gallon tank. The air pressure in the tank then forced the gasoline/oil mixture to the carburetor through a second rubber hose. The two hoses were molded together as one unit side by side sort of like a zip type extension cord.

The problem with this system was one of safety. If the fuel hose was cut or broken, the air pressure remaining in the tank would cause all the fuel to flow or spray out, frequently inside the boat, causing a serious fire hazard.

To overcome this fire safety problem, many manufacturers then turned to using the air pulses from the crankcase to operate against one side of a diaphragm in a fuel pump. The diaphragm pulsing back and forth was used to pump the gasoline/oil mixture on the other side of the diaphragm to the carburetor. The fuel pump had a couple check valves on the inlet and outlet sides of the pump the same as a conventional automotive fuel pump. Two cycle outboards not having a convenient cam shaft to operate a conventional fuel pump from were limited in the ways they had to pump the fuel.

In both types of a system, a squeeze bulb hand pump was included in the gas line to enable the carburetor to be primed for the initial start so you did not have to crank the engine over by hand or the starter motor forever to get the gasoline/oil to flow to the carburetor.

It is possible to add a two cycle outboard motor crankcase type fuel pump to an older outboard motor (engine) that originally used the fuel tank pressurization method for the remote tank to eliminate this particular fire hazard problem.

You have to bore and tap a 1/8 inch or so pipe thread into one part of the crankcase (as per a cylinder) in which to insert the line connector to the new fuel pump. The line length must be kept relativly short so as to maintain the pressure balance between the seperate parts of the crankcase. Of course you will probably have some drilling and tapping chips get into the crankcase that you will have to clean out somehow or by dismantling the crankcase itself. If there is some sort of a cover or access port into the crankcase you may be able to remove it and install the new fuel pump port in, and thats all the better. The rest of the fuel pump installation is pretty standard with a fuel filter, fuel lines and so on.

This 7.5hp Evinrude is 1955 or 1956. Blue with white is 1955 and blue with black is 1956. Starting in 1963 the 2nd or 3rd digit of the model was the last digit of the year. Under 10 HP it was the second digit and on higher HP it was the third digit. We do not know how long this configuration was used. We think the single fuel hose started in 1958. Also the serial number(the second part of the number) started at 01001 for most engines from '58 thru '65. The exception was the 1964 3hp which was sold as the Lightwin, Ducktwin etc. Don't know if new tanks are available anymore but we do know the price would be prohibitive if they are. We had to pay over $60 a piece for coils on a 7.5 13 years ago. Hope the coils are good!