In my last post I described how my outboard went in the drink and how I quickly got it running again. When I returned from the Cape I made a temporary mounting board out of a couple of pieces of plywood while I waited for a Garelick replacement to arrive. While my mount is Fulton the Garelick mounting board was a hole-for-hole match and conveniently available (special order) from West Marine. So far, so good, but not for long. A couple of week later the outboard refused to start when we were preparing to drop sail and head home. We were sailing on the Shrewsbury, only a mile or so away from our mooring and not outside of any draw bridges, so we just sailed home - very light air but we made it. Engine off again and the second half of this sad saga begins. Through this period I got pretty good at moving my boat between the mooring and dock without power. I'd row out with 200' of line, one end attached to the dock, climb aboard and pull the boat in on the line. It is a lot easier to remove/install the outboard with the transom right at the dock than doing it from a dinghy at the mooring. At the dock, the outboard is never over water and I have to lift it only a foot or so to the mount. A lot safer.
The symptom of the failure was a very weak spark in free air that I could only see it in a darkened room. Once the plugs were in the cylinders there was no spark at all. There was not enough voltage to overcome the higher breakdown voltage of the compressed gas in the cylinder. There are four relevant components in the Honda ignition circuit. A magneto coil under the flywheel generates a voltage pulse that powers the electronic ignition (CDI) module. Another coil under the timing pulley on the cam-shaft tells the CDI module when to fire, sending a voltage pulse to the high-voltage coil and from there to the spark plug. A failure in any of the three coils or the CDI module would cause a hard ignition failure, but it was harder to explain just a weak spark.
It was hard to ignore that the motor had a dunking in salt water a few weeks before. Everyone knows that salt and electronics are a bad combination. But it was also hard to correlate that dunking with the present problem. The Honda service manual gives test information for most of the components but shows no voltage waveforms. That is a serious shortcoming. If I had the waveforms I could have quickly isolated the problem to the magneto power coil under the flywheel. But I had no waveforms and no access to a working motor to compare to mine. The only course I could take was to start replacing parts, none of which was cheap. Assuming that the dunking was the cause I started with the spark coil since the high voltage present there would be most susceptible to shorting from salt intrusion. No luck. Next was the CDI module. No luck. At this point I got fed up - the summer was passing and I was spending far too much time in my shop and not out sailing.
I considered a new motor but the cost was prohibitive for the amount of use I make of my boat. Instead, I found another used Honda 7.5 quite a bit newer than mine. Before installing it I compared its voltage waveforms to my motor. Immediately, the failure was obvious. I installed the power magneto coil from new motor in the old to confirm and indeed, that was it. The old motor now had a fine spark. I returned the coil to the new motor, bought a new one for the old motor, and I now have two working motors. I put the newer on on the Tanzer and the older one on my inflatable dinghy, which is fun for put-puting around the river a little further than I'd want to row. The irony here is that the coil that failed was the next one on my list to replace. Oh, well. An extra motor for backup and the dinghy is fine with me.
Did the dunking cause the power coil to fail? I really don't think so but I can't say for sure without opening it up, which is nearly impossible as it is potted in epoxy. First, the potting seals the windings, making it nearly impossible for water to get inside. Second, the coil failed with an internal short that reduced its resistance (and output voltage). It is unlikely that salt water would damage the insulation on the windings, causing a short. I think this is an example of a spurious correlation - an event that appears causally related but in fact is not. It was just the coil's time - the dunking had nothing to do with it.
With a newer motor on my Tanzer we finally got on with the season. But there was still the original issue of what caused the idle problem with the old motor, the problem that caused me to shift into reverse at an elevated speed, that caused the mounting board to break, that caused the motor to go in the drink. My best guess is that it was a problem caused by old gas or ethanol in the gas. I found a small amount of a gel-like substance in the carburetor fuel bowl that could easily clog the metering jet or other ports. Another day, another problem. That's the way is is with motors on boats.
Bill Wetzel
The symptom of the failure was a very weak spark in free air that I could only see it in a darkened room. Once the plugs were in the cylinders there was no spark at all. There was not enough voltage to overcome the higher breakdown voltage of the compressed gas in the cylinder. There are four relevant components in the Honda ignition circuit. A magneto coil under the flywheel generates a voltage pulse that powers the electronic ignition (CDI) module. Another coil under the timing pulley on the cam-shaft tells the CDI module when to fire, sending a voltage pulse to the high-voltage coil and from there to the spark plug. A failure in any of the three coils or the CDI module would cause a hard ignition failure, but it was harder to explain just a weak spark.
It was hard to ignore that the motor had a dunking in salt water a few weeks before. Everyone knows that salt and electronics are a bad combination. But it was also hard to correlate that dunking with the present problem. The Honda service manual gives test information for most of the components but shows no voltage waveforms. That is a serious shortcoming. If I had the waveforms I could have quickly isolated the problem to the magneto power coil under the flywheel. But I had no waveforms and no access to a working motor to compare to mine. The only course I could take was to start replacing parts, none of which was cheap. Assuming that the dunking was the cause I started with the spark coil since the high voltage present there would be most susceptible to shorting from salt intrusion. No luck. Next was the CDI module. No luck. At this point I got fed up - the summer was passing and I was spending far too much time in my shop and not out sailing.
I considered a new motor but the cost was prohibitive for the amount of use I make of my boat. Instead, I found another used Honda 7.5 quite a bit newer than mine. Before installing it I compared its voltage waveforms to my motor. Immediately, the failure was obvious. I installed the power magneto coil from new motor in the old to confirm and indeed, that was it. The old motor now had a fine spark. I returned the coil to the new motor, bought a new one for the old motor, and I now have two working motors. I put the newer on on the Tanzer and the older one on my inflatable dinghy, which is fun for put-puting around the river a little further than I'd want to row. The irony here is that the coil that failed was the next one on my list to replace. Oh, well. An extra motor for backup and the dinghy is fine with me.
Did the dunking cause the power coil to fail? I really don't think so but I can't say for sure without opening it up, which is nearly impossible as it is potted in epoxy. First, the potting seals the windings, making it nearly impossible for water to get inside. Second, the coil failed with an internal short that reduced its resistance (and output voltage). It is unlikely that salt water would damage the insulation on the windings, causing a short. I think this is an example of a spurious correlation - an event that appears causally related but in fact is not. It was just the coil's time - the dunking had nothing to do with it.
With a newer motor on my Tanzer we finally got on with the season. But there was still the original issue of what caused the idle problem with the old motor, the problem that caused me to shift into reverse at an elevated speed, that caused the mounting board to break, that caused the motor to go in the drink. My best guess is that it was a problem caused by old gas or ethanol in the gas. I found a small amount of a gel-like substance in the carburetor fuel bowl that could easily clog the metering jet or other ports. Another day, another problem. That's the way is is with motors on boats.
Bill Wetzel
