This 1976 Honda Trail 90 came to us with the task of “get running”. First, we checked the spark by taking the spark plug out and grounding it to the cylinder while kicking the motorcycle to turn the engine over. We observed a peculiar “double spark”- it would spark twice in rapid succession and then skip sparking altogether for a revolution or two. As we haven’t observed this before, we discovered that we had a puzzling problem on our hands.
Our first inclination was to suspect the ignition coil. Unfortunately, with a new ignition coil our symptoms persisted. There are times when diagnosing can be what John often refers to as a “pig in a poke”. We have to start trying to alleviate the symptoms somewhere, often blindly but with an educated guess. This approach is utilized only when there is a strong suspicion that the part may need replaced and the methods required to prove that it does not would exceed in monetary value the amount to simply replace it. That is to say that if the replacement part only costs $20, but would require 2 labor hours to prove it is bad ($160 in labor charges), we would default to just replacing it because that it the most cost-effective solution for the customer. In some cases, such as a CDI box, once every other part is eliminated the only method by which you can prove it it is bad or not is to replace it. There is no “test” that can be performed to diagnose.
Next we started looking at the points and condenser. At first glance it visually appeared that everything was in working order. We couldn’t identify any loose wires or bolts and there weren’t any shorts to ground.
Although the points and condenser passed the visual inspection, we knew we needed to ensure they were gaped properly and opening/closing at the correct time. We started by going through the process of setting the point’s gap with a feeler gauge. First, you gap the points at the widest position. When we did so we noticed the points would also open very slightly at 180 degrees from where they should at the lowest part of the cam (what we call the “heel”). They should open while approaching the highest point. We determined that there was either enough wear to cause this or that the camshaft was slightly bent, therefore causing the point’s opening to be out of phase.
Next we readjusted the point’s gap minimally to alleviate it opening out of phase which allowed us to achieve one good spark. Then we set the crank at “fire” and made sure it was on the proper stroke. There are three marks on the crankshaft: F (Fire), TDC (Top Dead Center), and ADV (Advance). Additionally, there is either a fire or exhaust stroke, and it needs to be on the fire stroke when performing this procedure. Simply put, the piston comes up once and fires and on the next time it returns to the top it will exhaust.
Often we use a test light to aid us in this process because it will show you at what exact mark the point’s break (which simply means at what point they open/spark).
Through this process we discovered that it was both out of time and the point’s gap was also improperly set up. After adjusting everything to proper specs, we were able to fire it up and hear it run.
After it was running, we were able to hook up a timing/strobe light which allowed us to further fine-tune the timing as opposed to static timing it on the bench with the engine off. Once running, the strobe light allows us to see precisely when the spark is occurring, when it is advancing, and to how many degrees.
We were pleasantly surprised by how well this one ran once the job was complete and were thrilled to return this nostalgic piece to its owner in good running condition!
