Troubleshooting cranking issues - 1983 Mercury 115 Tower of Power

Jaybird73

Cadet
Joined
May 16, 2020
Messages
10
TIA for help coming up with a troubleshooting priority checklist for my 1983 115. Here's the facts:

I bought this boat 3 years ago after having not owned a boat for many years. I had had a Donzi Z21 half a lifetime ago. Just wanted a cheap but dependable little combo boat to go cruise the nearby AL river and possibly tow up to a lake occasionally. Bought a late 80's little bowrider that I could also fish, jug, and take the kids tubing.

Shortly after I bought the boat 3 years ago, we had a very rainy summer and my local section of the river got very high. By August, I had to get back to other issues, so it was run briefly only once in '17. Stayed in an enclosed dry shed for the next 3 years as I didn't have much free time in the summers of 18 and 19.

Finally gotten it out and cleaned up. I drained the old fuel and trickle charged old battery. Also changed the fuel line between the bulb and motor. The hose barb is may be 1/8" a little undersized for the fuel line, but I have it worm clamped tight.

Ran it yesterday. Took a little bit to get it started with a charged up older battery. Finally started and it did great except I ran it out of fuel about 300 yards from our put in and had to get a tow back. Gas is gauge is broken, btw.

Went back today with a brand new NAPA marine battery and full 24.5 gallons of fuel plus 2 quarts oil. It ran great again. Took a moment to get it started but not much trouble. Engine sounded wonderful. A friend was with me and after a long cruise of around an hour or more, I shut it down. We put our tubes in the water and a long float downstream of around an hour. After that, it was no luck starting. Tried choking it multiple times. Several times it almost hit, but failed and turned into a humming sound. Bulb would pump until hard. Had to float down to marina entrance and get a pull in. Appreciate your insights or starting points in diagnosing this.
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
28,141
To be clear, the starter turns the motor, right?

An obvious start would be to check to see if motor has spark on all cylinders. If it does, take a compression test and see if all cylinders are about the same in compression PSI.

If both of those are good, spray some 50::1 fuel into carbs and crank her. If she starts and runs a bit, likely the carbs are dirty.
 
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