Johnson Stinger 70 timing?

[Ricky_rich]

I have recently bought a 1974 Johnson Stinger 70hp.
The engine has not been used for about 15 years. Had to clean carbs, replace a coil, and put in new sparkplugs and new coals in starter. Then I got the engine running, but when I was out on the lake the engine felt a bit week. The previous owner had run the boat at 50mph, but I could only get it to run 34mph.
I took a look at the spark timing with a timing light. Look at the two pictures attached. From what I can see I have the spark after TDC, that can never be right from what I know? I get som spark advance whith higher rpm but I'm far away from where I should be.

 

[racerone]

Those pictures are , they with the motor in gear out on the lake ?-----Or just on the trailer and running on a hose ?-----The timing does not go out of adjustment on these motors.-------You only need to check MAXIMUM timing advance at full throttle.------Idle timing looks after itself.-----Careful if you decide that adjustment need to be done.-----What other trouble shooting was done ?-----What kind of boat can go 50 MPH with a 70 HP motor ?

 

[Ricky_rich]

I have only checked spark at home on the trailer with a hose, no gear. Guess I have to do it WOT out on the lake before doing anything else.
What else should I check aside from the things I've done?

Here is the boat, barely 15 feet.

 

[racerone]

Do a compression test first.-----Then look for spark that jumps a gap of 3/8" ( 1 cm ) on all leads.----Report your results of these tests.

 

[Ricky_rich]

I have a compression tester so that's easily done.
But the spark test you are talking about, should I get a tool like the one in the picture for that? Or can I let the spark jump to ground?