1985 15hp johnson starts, runs dies

[Blu_Cs]

I have a 1985 15 Hp Johnson, electric start. A beauty. This problem is new.

I always run ethanol free gas in it, with OMC oil and a maintenance dose of sea foam.

​It starts and runs fine but after a minute or two just dies, this is when in neutral or in gear. (Always with the earmuffs on).

​To restart I always have to set on choke.

​Tank vent is open, fuel pump good and tight, fuel flowing into carburetor.

What next? Thanks!

​Blu-Cs

 

[rolmops]

You have a fuel supply problem. When you start the engine the little reservoir in the carburetor is full,but as the engine runs it uses that fuel and it is not replaced as fast as it should be. I would start with checking all the fuel filters. In the tank and the one in front of the fuel pump.If those are clean,the next check is the fuel pump. Disconnect the hose that goes from the pump to the carburetor ,at the carburetor end, stick that end in a bottle and pull the starter. If you have a good stream of fuel,your pump is ok. Next would be replacing the fuel lines between the tank and the pump, starting with one with the ball, sometimes the check valve goes bad or there is a pinhole in the line that will draw air towards the pump instead of fuel. Same thing goes for the fuel line from the quick connect to the fuel pump.On an off chance,you may have water in your tank,but it does not sound like it
That should just about cover it.

 

[oldboat1]

^^good suggestions.

I would get rid of the Sea Foam and the muffs -- don't need to run solvents for maintenance, and the motor runs lean on muffs. In particular, avoid revving on muffs.

Test in the lake or with the l.u. deep in a barrel. Back pressure is required to tune. 50:1 fuel ratio.

 

[Blu_Cs]

Problem solved. I replaced the fuel pump, but the key thing in my mind was the gasket underneath. It was hardened and had been cemented in place. I removed the old gasket, cleaned the mount off, installed the new gasket and pump, and she ran like a champ! Thanks for your help!

 

[rolmops]

Good for you! Now do not throw that old fuel pump out. That gasket is the diaphragm and it provides the vacuum action that makes the fuel flow. It costs less than $10 dollars to replace. On the other hand,the fuel pump does cost a bit more. If you get the diaphragm and add it to the old pump, you probably will have a fully functional spare fuel pump.