I have sons your age.
Pinging is normally from an engine that is out of time or a bad setting on points. When ever you install points you must set the timing after then adjust the carb and set idle.
These motors are good engines, but as with any motor their are certain maintenance issues you must do to prevent problems.
Have the tech you go to install an electonic ignition and get rid of the points and condensor as I mentioned in another post. You will be glad you did!
As with any motor the operating temp must be right. This motor being an aluminum block makes it imperative the the temp never gets over 185. Norm operating temp 135 to 160. As I mentioned in other post change you anti freeze yearly. Keep your outdrive pump in good condtion. Never run engine out of the water without being on muffs. Change out drive water pump impeller every two years. Change elbow / reservoir every 3 years in run in salt water. You can check if you hold your hand on front of res. to hot to keep it there, hold hand on back cool to touch. Engine must to warmed up and running. Clean heat exchanger every couple of years. I do this by taking it off and using a gun bore brush.
Buy yourself and Seloc or Clymer repair manual for year of engine and outdrive.
I learned these things the hardway, cost me big bucks so I educated myself and do much of the work now.
Motor is simple to work on, send otdrive out for work as the tools todo the job cost to much.
When I got my boat and I had a few problems and was on forums looking for ans. a guy from NC e mailed me his phone number and told me to call him. I did, he had owned this motor for a long time and clued me in on alot issues.
I will send you my number and you can call if you wish.
I Ris Early