A new diaphragm is about $6.00 or so.----Can't find one then make one.-----The instant nature of the miss would indicate an ignition miss.----The trouble shooting on these motors is so easy.
The driver coil is common to both cylinders.-----Points must be absolutely clean.----Check al wire connections.------Use timing light to try and pinpoint if upper or lower cylinder has the miss.----You have of course checked the fuel pump diaphragm.
Lap the tapers together with fine valve grinding compound.----The key locates the flywheel for proper timing.----The flywheel is driven by the locking tapers !
Replace breaker points and condenser and rotor.-----If that does not fix it perhaps the coil is aged and cracked.---Spark would jump to ground.----Removing the magneto requires marking the parts so the belt timing can be set correctly on assembly.
Best , as in most economical way is to keep your eyes out for a donor motor.----1993 and newer model 9.9 and 15 HP 2 strokes.-----It also depends on whether you want tiller electric start or going to a remote electric start set--up.-----E-bay might help out here.
Perhaps the tachometer is set wrong.----What number ( on back of the tachometer ) is it set at ?-----At an actual 7000 RPM the motor will not last long.-----What pitch prop is on this motor , a 15" or 13 " pitch?
Have you checked oil pump output ?------Check compression , post your numbers.----Test spark.---It must jump a gap of 3/8" on all leads.----Water in the fuel ?-----I can not see or hear your motor so up to you to do some checks.----Why are the 2 leads on the oil tank unhooked ??
On a say 1966 Evinrude / Johnson you can put an entire new ignition system on for about $100 or less.--They will also run on one cylinder because each cylinder has its own ignition system.--On some new 4 strokes an entire new system is like $1500.---When some parts fail the motor stops and will...
Post a picture of the carburetors.----Something is going on here with the decals on this motor.----Post a picture of the lower unit and or the water pump impeller and housing !
Antlergang----It sounds like your motor is running on just 1 cylinder.----Post compression test numbers.----And does spark jump a gap of 1/4" or more on a simple test device ?
A donor motor is you best bet.----Any thing for the 18 / 20 / 25 HP 22 cubic inch model only from about 1958 to 1976 will have the parts you need.---Great , durable , easy to fix and own motors.
