75 HP speedifour outboard engine

[akican]

The previous owner told me that the engine's model is 75553S. I had spark in all four spark plugs, and I had hard time to start the engine. Sometimes, I can start the engine with the first ignition. I am thinking to rebuild the carburetor and do a tune up. Could you please help me to find out what are the part numbers required for the above jobs. Thanks.

 

[Evinrude Boater]

Re: 75 HP speedifour outboard engine

Welcome to iboats. Your motor is a 1965 model. You likely have a distributor at the back of the motor driven by a notched belt. There are two sets of points and condensers under the plate on top of the distributor and a magneto to generate the voltage for the spark.
We don't know the history of your motor but you may be able to clean and adjust the carb and ignition to get it running properly. Personally, I have taken my carburetor apart at least six times and cleaned it. Finally after blowing out the orifices with compressed air the boat starts like it was intended. I've had my motor for three years and have only replaced the spark plugs and one spark plug wire. A little troubleshooting will help you determine what you need to replace instead of just blowing money hoping it will help. Make a manual your first purchase and get to know your motor; believe me it helps.

 

[akican]

Re: 75 HP speedifour outboard engine

Thank you very much for your quick response. Indeed, the engine I had that looked exactly according to your description. I believe that the distributor will move back and forth according to your throttle speed setting. The service manual has been ordered. Would you elaborate how to clean the carburetor and hoe to performed a timing check. Thank you.

 

[Evinrude Boater]

Re: 75 HP speedifour outboard engine

You'll need to take the carburetor apart to properly clean it. There are lead shot plugs and other larger plugs that close off areas of the carburetor. I didn't remove any of these plugs but a complete overhaul may require removal of these plugs. The main areas are the main jet and float, slow speed adjustment needles and the fast speed jets. I found that the rubber O-rings in the slow speed needle openings deteriorated and small bits of rubber made their way down into the needle seat. The main problem with carburetors is varnish from old gas deteriorating and drying up in a sitting motor. You'll need carburetor cleaner to disolve the varnish build-up and compressed air to blow out all the orifices.
Timing is described in the manual but if you've got it running, it's close enough. There's a procedure call link & synch that is very important. This is what determines how a much and when the distributor rotates to advance the timing. You might find a detailed procedure on iboats if you search this forum.