It's all in the Timing...
It will be another generation or so before somebody says, I remember the good old days when we had points and condensers and a thing called a distributor to make our engines run..... Until that day there isn't any reason to believe they are going to go away tomorrow. It will take at least another 15 years to retire 80% of the equipment that is in the field right now.
It's been a good policy to convert over to electronic Ignition where possible, but the good marine replacement Distributor Ignition isn't an inexpensive thing to buy, especially when your doing twins.
As these units age, the customer still  expects them to run properly, so learning some of the basics won't hurt.
The manuals pretty much cover the basics of doing a tune-up so my purpose here is to remind you that all boat distributors use a counter weight timing advance. Under the points plate you will see this centrifugal advance mechanism. Look to see it's condition and that both return springs are clipped in place and functional. They have a tendency to rust, stretch, and break so make it a part of your tune-up to check to see if the timing advance is working correctly. The timing advance and return is very important to  the performance yet it's probably one of the most overlooked tune-up operations.
On the average engine, the timing should never move, when the engine is between 500 and 900 rpm, and many shouldn't have any timing advance until 1100 rpm. It's getting tougher to find a good distributor rebuild shop, but if you see any sloppiness in the timing when the engine is idling, it's best to have the distributor serviced.

Note: We are referring to mechanical advance distributors. Timing advance on an electronic controlled ignition will  continuously change at Idle.

The time that the points  are closed is your dwell, close the points to increase the dwell, open them to reduce the dwell

Remove to access the centrifugal advance .

Note that one spring is for low rpm and the larger is high rpm (yellow arrows)
Check for rust and wear at slots (blue arrow)

dist-rust

(Example of damaged distributor advance mechanism.)

 

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