1980s Mariner 4 hp-no telltale, now won't start

I just bought a Mariner 4 hp, 80s model, that ran good at the time of purchase. I test ran it several times once I had it on my boat and it started OK, not great but OK, had a little bit of trouble shifting gears, but it pumped well. It had a nice strong telltale. The first time I took it out I started it, all Ok, pumping great, motored out and about a minute later I looked back and saw that it wasn't pumping. So I shut it off immediately and got a tow back to the dock. It won't start now. I just want to know that I couldn't have possibly wrecked the motor in a minute of running it without it pumping water. I also wonder if the previous issues I was having could be the reason it's not starting and that the pumping is an unrelated issue (likely the impeller.)

The issues I was having before were that the motor only wanted to start at higher speeds, ie I would have to set it above "Start" on the throttle in order for it to, well, start. It would also not always shift into neutral when I went to shift from forward. It seemed stuck. It also refused to start with the choke on it. Would this be a carb related issue and would this be a reasonable explanation of why it is not starting now?

I really know nothing about motors, I know how to take care of one that is running good but when things like this happen I'm pretty lost. I'm still learning. Thanks in advance.

So I got the motor to start but it runs really rough, and I do have a telltale. I'm starting to suspect a blown head gasket. Could that have caused the engine to overheat in the first place?

Do a compression test...carb probably is dirty and needs a good cleaning. Drain the carb or run it until the carb is out of gas. Remove the fuel line to the carb and spray it full of spray type Seafoam and let it soak for 48 hours then try to start it up...it will smoke like crazy and should run better. Fuel pump may need a rebuild.