When I put my r65 back together I knew I had to find a replacement coil, the bike was still fitted with its original, genuine "Crack-O-Matic" which, true to its type had lots of cracks and the I recall the PO telling me that for some time before the valve drop that was the catalyst for me becoming its owner, he was unable to ride on even "moist" days because of the bike being hard to start and misfiring.
I did my research and knew i was looking for a 1.5ohm, dual output coil. I found some fitted to a ancient Mercury outboard and, as the price was so good, I bought two of them. Given the price of new Bosch coils or the Dyna replacements that seem the popular alternative I felt quite conceited in my cleverness.
Roll forward to a few months after my R65 was registered. It started misfiring horridly below 1,500rpm and sometimes seemed to be ready to come to a complete halt.
I made up new ignition leads and that sort of fixed the problems - briefly.
Then a couple of months ago, on my way home the ignition amplifier failed. I replaced it and again everything was good, that was until the weekend before last when the wife and I went for a ride which ended up with me limping into the small town of Mareeba running on 1 cylinder, missing and farting like crazy and totally unwilling to rev beyond 2,500rpm.
In retrospect this should have been a big clue, but I misinterpreted the clue and when the thing ran perfectly after me mucking about with it in the blazing sun for 30 minutes I leapt to the conclusion that I had a heat related problem with either the coil or the nearly brand new ignition amplifier.
Ever willing to spend money on the least expensive possible fault, I went to the local European auto wrecker and bought some 2nd hand ignition modules from an old VW and an old SAAB. They both worked which set off the smug conceit circuits in my brain, but when I went for a ride the following weekend , coughed and backfired under 1,500rpm and would still behave as if the ignition was being randomly switched off.
Then I did something sort of smart, I grit my teeth and bought a genuine Bosch coil from Motobins - nearly $AU200 south Pacific Pesos.
It arrived yesterday, so this afternoon I fitted it.
As the old ignition leads had already been cut and modified to suit the Mercury "TEC" coils I made new ones up using some NGK resistor caps and solid wire core ignition wire I've had for a while (sorry neighbours you don't need no steenking TV or radio reception when I tune my motorcycle).
The bike runs beautifully......Yay.
But in the course of removing the old Mercury/TEC coils I found the real problem.
You see those coils are so "hot" that the spark plug wire for the left hand pot had been flashing through and grounding on the starter-motor cover. Looking closely you can see the pock marks of literally tens of thousands of individual arcs having gone to ground through the cover, more to the point the insulation of the spark plug wire was completely brittle and cracked where the flash-over has been happening.
One very large DOH moment.
Every time I have thought I had a "cure" what I had really done was move the LHS spark plug wire a little so that it then took a while to break down a new section of insulation.
My supposed heat related problem wasn't that at all (although it did nicely fit the facts), once again in my mucking about trying to "move" the fault, I had of course inadvertently moved the LHS spark plug wire.
The joke is on me, because had I realized the true nature of the problem all I needed to do was use better insulated spark plug wires or (and here is an idea) an in-line resistor to pull the coil voltage back to around 8~9 volts and wire a relay into the starter button circuit to give the coil a full 12 volts when cranking and I suspect that I would have never had another day's trouble. And I would have saved over $200.
The moral of the story.
If you are having ignition trouble, check your spark plug leads for signs of insulation breakdown, and if like me you make your own, slip a piece of larger diameter tubing over the LHS spark plug wire so that it is protected where it rubs on the starter cover.
The laughter (at me) can now commence
