1975 johnson will start and run but will not start again.

[Tallboy610]

Hello all,
I bought a 1975 johnson 25 hp model 25R75B. Filled up metal tank and took it to the lake. Drop the jon boat into the water, motor fired up and idle until I returned from parking the truck and trailer. Ran fine on the water until you slow down and proceeded to die but would start back up and returned home to clean the carb. Needless to say, I have cleaned the carb by pulling out 3 metal plugs and soak in Acetone. Reassembled card with rebuilt kit added new fuel line and in line filter. Motor started in tank and idle for 10 minutes with a little throttle. Took it 5 miles to the lake and now it will not start. Disconnect kill switch still same result.
Compression 135.
​Point gap .020
Plugs Champ J4C and gap at .030
Spark jumps to .50


Pulling hair out is and understatement considering my arm is still attached to my body from trying to start motor. Any help is appreciated. Thank you!!

 

[Triumph55]

Good spark at the right tine, fuel and compreesion all ot needs. You need to check while it is acting up. Is it overheating?

 

[Tallboy610]

That is what I believe. Its not overheating that I am aware. Thermostat is working once it reaches temp, water begins to flow out drain. If I can get it started again I will check.

 

[James R]

Could be several things. Great little motor, I have one on one of my boats. Could be dirt or rust in the fuel tank blocking the pick up tube. Usually the fuel pump sucks all the fuel it can get and collapses the bulb. If there is an air leak in the hose prior to the bulb the motor will use all the fuel it can get until the air leak overtakes it. In that case the bulb will not collapse. Check that the sparks are good and not breaking down. If it wont start mix a fuel mix in a spray bottle, remove the air box if it has one and spray fuel into the carb throat. Try starting then. If it fires then you know it is a fuel problem. Try running the motor on a gallon jug of fresh fuel to prove the tank problem.

 

[Triumph55]

That is what I believe. Its not overheating that I am aware. Thermostat is working once it reaches temp, water begins to flow out drain. If I can get it started again I will check.

There is no "drain" when the thermo opens.
Water should come out the releif hole in back of exhauat housing heavily as soon aa engine is runni . Hot or cold.

 

[Triumph55]

With a good w/p water will pump even when cranking.

 

[Tallboy610]

James i didn't think of the gas tank being the problem. I will give it a shot this weekend. Thank you for your suggestions.

 

[Tallboy610]

Triumph55 outboards our new to me, two-stroke are not. I thought the thermostat only opened once it reaches operating temp. I will look into it. Thank you.

 

[Triumph55]

It does, but it being open has nothing to do with water flow out of the outlet on the back of the exhaust housing on these engines. It should have heavy flow immediately at start up.