Rookie question, need help please!!!

Check the primer bulb when it shuts off. If it isn't hard, then it may be either the fuel pump, fuel filter leak (had this happen), or the fuel line and bulb itself.

 

It could be a fuel issue, but it might be overheating. How is the water pressure now? Maybe it has some clogged water passages inside the powerhead?

 

I just dealt with this issue myself and I doubt it's that. Not to mention my old Mercury overheated to the point of steam coming out of the tell tale on multiple occassions...it never shut off. I would think if it's overheating to the point of seizing, it would only happen once and he wouldn't have the opportunity to start it again. Just my opinion, though. I'm sure as hell no expert...just basing off of my VERY limiting experience. His symptoms sound more to me like fuel starvation.

My Yamaha's fuel filter assembly had a leak a while back (ethanol ) and it was doing the same thing his is doing. I'd pump the bulb in the morning, start it up, ran perfectly for a few minutes, then it would shut off. Wouldn't start back up. Then I'd pump the bulb to give it fuel and repeat the process to get back to the ramp. When I got back, I noticed that when I pumped the bulb, fuel was coming out of the o-ring area of the fuel filter assembly. In a pinch, I ran to West Marine and replaced with a cheap in line. The cheapy is still in there and it's running great.

 

If the carb work is still good, I would check the fuel pump.
Older johnson fuelpumps dont like to sit for a couple years then be forced to start flexing again.

 

Agreed on the fuel pump diaphragm.
the old neoprene diaphragms weren't intended for use with e-fuel.
I had to replace a neighbors pump recently,
'93 model 'Rude with a 3 year old pump, pulled it apart
and the diaphragm was brittle, no longer flexible.

 

is this a 2 cylinder model?

 

It could be a seizing issue. I am dealing with a similar problem now as well on a 40hp. My motor stripped a driveshaft and was replaced. When the foot was put back on, the waterpump tube did not line up. Motor was run for about 200yards and slowed, lost power and seized. 10 minutes later it would start. Took apart, and fixed water tube issue. Now motor starts fine, runs for 10 mins and looses 50-75% of power and then starts to sputter.

After overheating, I found that ALL of the head bolts needed about a half turn to tighten. I'm hoping current issue is head gasket blown, but I'm not holding much hope. I think she's toast! Looking for newer motor..

 

Q and A time
Since it is a 92 i'm betting there is no filter one other than perhaps a simple screen some where inside the carb.

When you say run do you mean rev up and push boat or idle?

As rkmurphy asked when it dies it the fuel bulb hard? That will tell you about either a vac leak in fuel system or a failing fuel pump. If the fuel bulb is hard this points to two paths to follow electrical or mechanical issue.

If you let it cool completely does it restart and run for another few min?

Know anyone with a compression tester? we can eliminate the scary motor stuff pretty quick this way. and it's nice to find out the baseline for your motor for future reference.

When it dies pull the pugs and look for spark with plugs you know to be good.... helps to have a helper for this.

Answer the above and I can get into some more electrical trouble shooting but you'll need a volt meter.

Where are you some one might live nearby that can lend a hand/knowledge/ and or tools. The more info you can provide the better we can help.