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!

Engine temperature when it's running won't have any effect on the choke

As a couple of places to start I'd be looking at the impeller in the RWP and looking to see if there's a thermostat in the engine instead of wondering if there's one in there 

With or without a thermostat, the cooling system will draw water in right away.and it'll be coming out the exhaust. 

Without a thermostat, it's always going thru the engine and exhaust manifolds. 

With a thermostat it's always going thru the exhaust system and can only exit the engine when the thermostat opens 

I'd like to agree that you need to check the RWP rubber impeller, check all cooling hoses and the sea strainer for air leaks as well as confirm there's a T stat on your engine. 

I'd also like to say that running on the hose in the driveway is NOT a good way to diagnose a cooling problem. The water pressure from the hose masks all cooling problems. Use the bucket or "Timmy T" method. 

I feel you have a cooling system problem and NOT a carb problem. 

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.

You probably have a cooling system problem and a carburetor problem based on the link below 

http://www.correctcraftfan.com/forum/forum_posts.asp?TID=49207&KW=&title=1983-ski-nautique-351-idle-stall" rel="nofollow - link

Thanks again.

Martin

Martin,

Where did you disconnect the hose? At the through hull or at the RWP? I ask since if at the RWP, you bypassed the sea strainer which can be a issue with cooling. Were you able to get the time it took for the water to be pumped from the bucket? That is a good indicator of the RWP performance.