1973 Evinrude 40Hp seems to run on one cylinder only

[reilley]

I replaced the spark plugs on my outboard and the fuel hose from the tank (old fuel hose seemed to thin since primer was sucked flat) and went on the lake. At first the motor was running great at full speed. After i switched it off and on again it would only run around half a speed in full throttle. First thing i checked were the spark plugs, in the first cylinder the spark plug looked nice brownish as it should be, in the second it was just wet and looked like i just bought it. To make shure i unplugged the wire from the second cylinder and run the motor again it was the same just about half speed. I tried adding a fuel adhesive that would bind any water that might have been in the tank and nothing. Then i tried changing the sparkplug in case it had been faulty still nothing.
Is there anything else i can try before i bring it into a marine repair store?

Any help would be appreciated.

BTW i used some seahorse in the fuel and spray in the cylinders to decarb before problem occured

Thanks
Chris

1973 Evinrude 40 HP
Model #40354D

 

[DJ]

Re: 1973 Evinrude 40Hp seems to run on one cylinder only

The primer bulb sucking flat is a sign of a clogged, or closed, fuel tank vent.

Was the 2nd plug wet with drops of water or fuel?

If fuel, switch the coil assembly from cylinder to cylinder and see if the spark moves from one cylinder to the other.

 

[Solittle]

Re: 1973 Evinrude 40Hp seems to run on one cylinder only

Check the compression at this point also.

 

[Paul Moir]

Re: 1973 Evinrude 40Hp seems to run on one cylinder only

Go ahead and do a spark test. You should be able to get both cylinders to jump a 3/8" gap pretty easily. If you've got no spark at all on one cylinder, disconnect and isolate the two small black wires that come down from up under the flywheel and see if spark returns. That will rule out a defective ignition switch, etc.