I think it will be very , very clear once motor is apart.---Good compression would be around 120 PSI.----So 70 PSI tells me a story !!----You said pistons " looked good " , where / how did you look ??
Take it apart.----Pistons on the bench and likely garbage.----Inspect every , nut , bolt and bearing.----Don't forget inspection / reseal of the gearbox.
Running a motor at 6000 RPM in neutral is a big mistake !-----Need to determine condition of this motor.----Compression test.----Post your numbers.------Or find shop with a dynamometer to see if motor is developing rated power.
I used to test coils with a ----MERC-O-TRONIC----Magneto analyzer.-----Coils are much more affordable today.----I never / rarely test today.-----Install new ones.
What is your motor doing / not doing ?-----There is very little that can go wrong with these simple carburetors.----Other than plastic carburetor bowl warping.
Helicoil is one option.-----I would make a new plug with a hammer and chisel.------Hint---Buy a 10 mm bolt.----File the head round.----Use hacksaw and fine file to put a slot in it.
Does spark jump a gap of 3/8" or more on both leads , yes or no ?----Checked the flywheel key.-----Water in fuel.-----Have you cleaned the carburetor ?----Orange / blue stripe on the top coil ?
Should be the same as Suzuki.-----What parts are needed ?-----Yes the availability of spare parts from the " new age " corporations can be a problem.----I just ordered 2 crankshafts to fit 1961 model 5.5 HP Evinrude / Johnson.----No problem.
