Possible Removed Thermostat Cause Stalling?

I have a new to me 1982 Ski Nautique with a 351 Pleasure Craft engine. I was out for the second time with it yesterday and noticed at high speed the temperature shot up near to 240 degrees, so I dropped down to idle and it quickly cooled down. As I putted round the lake I noticed the thermostat went down below 100 degrees and it ran rough and stalled. I had to wait about 10-15 minutes before I could start it again. It is now occurring to me that maybe it is running too cold at idle and the electric choke kicks on? I am pretty sure the thermostat has been removed as it draws water right away in the driveway.  I removed the carb and was going to get it rebuilt... but maybe it is not a carburetor issue?

I guess I have two questions: 

1. Is the scenario above possible that the electronic choke would engage if the engine got cool enough and flood/stall it out?

2. It only makes sense the way ti acts at idle (cools way down) that the thermostat was removed. What could be some of the reasons it spikes hot at high speed?

Any insight would be very appreciated.

Thank you!

143 or 160 degree thermostat will work.

Don't ask which is better unless you want to watch people argue and tell you their personal preference 

The boat originally would have had a 143 from the factory though if it'a a normal raw water cooled engine.

You can probably find the setting marked on the thermostat. If it's pretty brownish you might have to clean it up to have a chance of seeing the numbers.

Thanks again.

Martin