1975 evenrude 15 hp runs good in a trashcan but bogs when lake tested

[jdgeracesr]

I have a 1975 evenrude outboard motor, model154045, serial 0003163. I have replaced the pickup under the flywheel, the fuel and water pump, spark plugs and cleaned the carb. I am using a new fuel tank and supply line with fresh fuel. I can run the motor for as long as I want if it is in a trash can. In neutral and in gear it runs good, I can not lake test it because every time I do it begins to slowly idle lower and lower until it stalls when in gear, the fuel bulb on the supply hose is hard and pumping it does not help. If I am idling the motor in the lake I have had to richen the fuel with the knob on the front of the motor after the engine has run for a few minutes. This engine does not have a lot of hours, maybe 3 or 4 hundred hours as I purchased it from the origonal owner 25 years ago. My gut tells me to replace the carb but also tells me the engine is acting like its fuel starve like the vent on the gas tank is closed but it will run for a long time in a trash can so I doubt that is it. Once it stalls it is hard to start. Dang near impossible, even if I give it a little squirt of volitile brake cleaner (yes I know this is very bad and should not be done). Any advice will be appreciated. Thanks in advance

 

[racerone]

Answer these-----Is the thermostat installed and working properly ?-----Does spark jump a gap of 5/16" or more on both leads ?----What are the compression test results ?----Tried opening the low speed mixture needle ?-------In a barrel there is lots of exhaust in the water, thus a reduced load on the motor.

 

[oldboat1]

Might make sure the choke plate is tightly closing for cold starting, and fully opening for running. The choke knob has to be installed with the long notch facing down. The slot accepting the choke lever is beveled so the lever will fully open and fully close the plate.

 

[OptsyEagle]

The first thing I would do is confirm that both cylinders are working. These things can idle remarkably well on one cylinder but of course with insufficient power when trying to push a boat. To do that, fire it up and let it warm up. Then with a pair of insulated pliers pull one spark plug boot at a time. If the motor stalls when one is pulled it means the other cylinder was not firing or was weak.

The next thing I would do is turn the rich/lean knob a 1/2 turn counterclockwise (more rich) and see if that gets it to quit stalling. You could try another 1/2 turn if it doesn't, but if it doesn't help then turn it back to where it was.

I would also confirm that your link and sync is good. On the throttle cam (the metal piece that pushes on your carburetor when you turn the twist grip) you will see an indented arrow. When you turn the twist grip that arrow should be in the middle of the carb's roller JUST as it touches the roller. If it is not, there are two hex nuts on the starboard side of that cam that can be used for adjustment.

If none of that helps then it is back to basics. You will need to confirm that you are getting spark on both cylinders and it can jump at least a 3/8" gap when using a spark tester. You should check the compression of each cylinder and they should be within 10% of each other. If you can pop the flywheel, confirming that the point gap is set properly at 0.020" would then be my next move. Lastly, that model was very prone for fouling spark plugs. I would try another set to see if that might be a problem. Get rid of any Champion plugs and exchange them for NGK B6HS or B7HS plugs. They resist the fouling problem a little better then the Champion plugs that are specified.

 

[kbait]

Oldboat.. the long slot on choke knob faces ‘up’...distal end of choke lever needs the extra length to fully open/close choke valve.

 

[oldboat1]

jdgeracesr -- might follow this diagram to check installation: http://ww2.iboats.com/Motor-Cover/dm/cart_id.343558889--session_id.912806535--view_id.1532426