1973 Evinrude 115 Starflite

[mercuryverado]

I have what I think is a 1973 115 HP Evinrude. I have been having some problems at idle speeds in F, N ,and R. Once I am on plane, the engine runs great and will take my boat close to 50. When I'm idling, it will make some thumping noise, and then rev back up, and then die down with the thump and eventually die. I am also having problems with starting it. Even when it is warm, sometimes I have to use the manual choke on the motor. Any help would be great! Thanks!

 

[oldrudedude]

Re: 1973 Evinrude 115 Starflite

What is the model number? How long have you had it? Have you ever cleaned the carbs/fuel system? Ever timed it or done a timing link synchronization with the carbs? Ever changed the plugs?

 

[F_R]

Re: 1973 Evinrude 115 Starflite

I have what I think is a 1973 115 HP Evinrude. I have been having some problems at idle speeds in F, N ,and R. Once I am on plane, the engine runs great and will take my boat close to 50. When I'm idling, it will make some thumping noise, and then rev back up, and then die down with the thump and eventually die. I am also having problems with starting it. Even when it is warm, sometimes I have to use the manual choke on the motor. Any help would be great! Thanks!

That "thumping" noise is called lean sneeze, and as the words imply is caused by running too lean. Those carburetors have fixed idle jets, so one on them might have crud in it. I believe you can remove the idle jets for inspection without removing the carburetors. However, don't jump to conclusions, it might not be dirty carburetors at all. Improper synchronization will do it too.

 

[mercuryverado]

Re: 1973 Evinrude 115 Starflite

What is the model number? How long have you had it? Have you ever cleaned the carbs/fuel system? Ever timed it or done a timing link synchronization with the carbs? Ever changed the plugs?

I have had this for about a month. I had it checked out and they replaced the water pump and cleaned the carbs. This motor was really close to getting fried because of the bad water pump. It has new spark plugs I'm sure, but I don't know about timing or synchronizing the carbs.

 

[ezeke]

Re: 1973 Evinrude 115 Starflite

For a quick check, take the air silencer cover off the carburetors and watch the throttle plates as you have someone move the control arm forward. The plates need to be perfectly synchronized throughout the full range of motion. They should be closed at idle and horizontal at WOT.

If the automatic choke function is still connected, you may want to disable that and use the toggle switch only.

I would be very interested in your exact compression readings, cylinder by cylinder.