Mariner 20hp runs when it wants

I have what I believe to be a late 80s mariner 20hp longshaft manual start engine. The motor will start cold most of the time sometimes it doesn't. I have had it on the lake a few times stats up runs great then wont start when it is warm. I have rebuilt the old carb same problems so I ordered a new carb and out it on same issues. So I dont believe the carb is my problem could be not 100 percent on that. The motor even when it was running good would shake a little at idle. Where do I go from here im going to give it a compression test when I get home will post results of that later on tonight.

My guess: Bad switch box.

Jeff

compression came back 100psi in each cylinder. I have never seen an engine with as much oil in the bottom cowl as this one so I started digging around there. Found 1 powerhead bolt missing and two others finger tight.

I have seen those come loose before too. Switch box is my best guess too. Confirm by doing a spark test when it quits running.

When you guys say switch box are you meaning the cdi box or the the electrical board all the wire hook into

Do a spark test when that happens. What is the model/serial# of your motor? Did you do a link and sync? Have you tried adjusting the low speed screw? Have you serviced the carb lately?