'77 Johnson 115 Dies after warm-up, in the water only

polvaultr

Cadet
Joined
Jun 12, 2013
Messages
11
Ok, so as the title suggests, I have a '77 115. On the trailer, she runs great, will throttle up, idle, and run gently in forward and reverse. I can let her run for 15 or more minutes. Then I go to put her in the water, and she dies.

Last year, she barely started when in the river. Looking through the shop manual, my dad recommended a new fuel pump (he paid, I installed, I was happy). I then noticed that there was obviously more fuel being fed through, as the zip-ties holding the lines to the pump weren't enough to contain the fuel, and it was spraying out some. Replaced said ties with clamps, made sure everything was in order, and dragged her off to the Potomac. She fired up beautifully with about 2 seconds of cranking (already better off than last year). Backed off the trailer, and motored over to the dock (still alive). Tied off, got out, and parked the truck (my wife is afraid to drive with a trailer since there were other vehicles around). As I am walking back to the boat, the motor stalled. I got back in, and she fired right back up and ran for about 3 more minutes (or 20' from the dock if you are a distance vs time kinda person). After that, she was done.

I could get a few seconds of run time with the warm-up lever engaged, so I tried dropping that and slamming in gear to get back to the dock. Needless to say, I have received my first "Tow of Shame" back to the dock.

My dad is thinking small, and start with least expensive fixes:
1. Fuel lines within motor.
2. Fuel line from tank to motor.
3. Carb adjustments (I did see some fuel leaking out of the bottom of lower carb, so I'm thinking he's on the right track).

Any suggestions? He's pretty handy with a wrench, and I know I still have plenty to learn from him, but an internet full of minds is better than the two of ours.

Thanks in advance!
 

emdsapmgr

Supreme Mariner
Joined
Dec 9, 2005
Messages
11,551
Check to see if the engine is running on all 4 cyls. That engine will seem to run just fine, when running on the trailer in the back yard, when actually only running on 2 or 3 cyls. You need all 4 firing when you put it in the water and shift it into gear. Weak ignition components tend to run ok when cold, then cause problems once the engine warms up to normal operating temps. You can test-once the engine is warmed up: either use an inductive timing light to see the spark flashes from each cyl, or: do a cylinder drop test. Either works fine. That engine has the following ignition components: 4 coils, a stator, a timer base and a single power pack. The coils are usually pretty reliable. This website has some really great ignition troubleshooting info on your engine: cdielectronics.com
 
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