0.020 in.
The points gap on a Merc 40 4hp is .020
To find out how old a 4HP Mercury outboard is, you can look at the label on the transom bracket, where you will see a two digit number giving you the year it was built.
A 4hp Mercury outboard requires a 50:1 fuel to 2 cycle oil mix.
Johnson 4hp outboard bj4brcud
Mine is a 2000 model and it has an NGK R BPR7HS10
You may have mistaken the '1' for a '2'..if your engine is a 4hp 2 cylinder it dates from 1978.
A 1998 model 4hp Merc outboard runs on a 50:1 fuel to oil ratio. This works out to roughly one pint of 2cycle oil to six gallons of fuel.
Jew
1969
1969.
The 4WF69B model, 4hp Johnson, would be a 1969 year model.
Try this site - http://www.marineengine.com/mfr/mariner_outboard.html