1990 50 HP Johnson Model VJ50TLESR Overheating problem

[1990Sunbird]

I have a 1990 50 HP Johnson motor and I believe it has an overheating problem. I can start it up OK and it idles fine, but when I throttle up and get between half and full-throttle it will stutter and then shut down after about 2 minutes. I can then start it back up OK and it idles fine again, but If I try to throttle up again it runs for about 10-15 seconds and kind of stutters and shuts down again. I am thinking that it is a thermostat problem and that I need new spark plugs, but was looking for any suggestions. I read somewhere that there is some kind of limiter on the engine that shuts it down if it gets to hot so that it does not ruin the engine and I think that this is why it keeps stopping.

I have ordered a new thermostat and spark plugs and they should arrive on Saturday. Shouldn't take too much to change these, but if this does not work does anyone have any suggestions?

I know that there is water coming out of the hose on the back side of the engine when it is started, but I have not payed attention as to whether water is coming out of the slot on the back of the engine when it is running. Water pump maybe?

Thanks in advance for any help!!

 

[1990Sunbird]

I have since replaced the plugs, thermostat, and water pump and this has not fixed the problem with the engine stalling after a few minutes. Their does not appear to be a good spark coming from the new plugs. This one has myself and my local marina stumped so far. Looks like this may be more electrical than ocerheating now.

Has anyone seen this with a VRO engine before?