Sometimes a simple repair is all it takes to get you back on the road.
Chances are that if your bike is a few decades old, it’s getting harder to find certain parts for it. I discovered recently on a hard-starting older Honda that one such item is the starter solenoid. For older Harleys this is a very common item, but for 35-year-old Japanese bikes, you might have to get creative when it comes time to getting your bike running again if the engine refuses to crank over.
Before we go further, though, let’s take a quick tour through the electrical side of the starter circuit. When you turn on the ignition and press the start button, current flows from the battery through a fuse (the first thing to check if the starter doesn’t turn over) to the starter button, and finally to the starter, though not directly. To fit the relatively small button in the handlebar switch pods, the copper contacts and the wires leading to them are tiny and can only handle very low current. The current required to operate the starter, as it cranks over the engine, is high enough to burn those starter-button contacts. So, what needs to be done is to bump up the current from about a couple of amps at the starter button to somewhere between 20 and 40 amps at the starter.
This is done in two steps. The first component following the starter button is the starter relay, which is usually a small cube with at least four terminals protruding from the bottom. When you push the button, you’re actually sending a small amount of current through a magnetic coil within the relay. When current flows through this magnetic coil, it pulls together a set of contact points, through which flows higher current than what can flow through the starter button. However, even here the current isn’t high enough to operate the starter, so it is instead directed to a starter solenoid.
Simply put, a solenoid is a much larger relay, and is identical in operation. It contains a much larger magnetic coil, which requires more current to operate than the starter button alone can provide, and draws together a much larger set of contacts. On older Japanese bikes, the solenoid is usually placed near the battery; it’s cylindrical in shape, and will have a pair of small wires and a pair of larger electrical cables attached to it.
There are a few things that can cause the starter to refuse to turn over when pushing the starter button. Very rapid, successive, loud clicking indicates either a weak battery or a loose battery terminal; the current is high enough to operate the solenoid, but not high enough to generate a strong enough magnetic field to keep the contacts solidly connected. A single, very light clicking each time the button is pushed means the relay is operating, but the current is either not making it to the solenoid because the relay points are bad or there’s bad wiring, or current is making it to the solenoid but stops there because the solenoid is defective. A much louder single click heard when the button is pushed usually means that either current is flowing to the solenoid but stopping there because the contacts are bad or it’s reaching the starter, but the starter is defective. Ticking at the relay or the louder clicking at the solenoid can be verified by simply touching each; you can feel the contacts snapping together.
The best way to troubleshoot the starting system is by using a test light and beginning from the bottom up, checking the flow of current to the starter, the solenoid, the relay, and finally the wires coming from and going to the starter button (yes, a service manual and wiring diagram will help you here). Starters can be rebuilt, relays are readily available, but solenoids, on the other hand, are a bit harder to come by.
In my case, a Honda CB400 had an intermittent start situation. When testing it, I found that the solenoid clicked loudly when pushing the starter button, but current didn’t flow out of it to the starter, at least not consistently. This indicated to me that the contacts within were at fault. A search of the aftermarket proved fruitless, so the next step was to repair the solenoid.
Fortunately, these old solenoids can be disassembled. Inside, the contacts consisted of a flat copper bar and two copper terminal studs, each with a contact surface, all of which were pitted. A very simple fix was to remove the two terminals and rotate them 180 degrees, and to turn over the flat bar, exposing brand-new contact surfaces on all of them, and therefore curing the Honda of its intermittent starting for probably another three decades.
Technical articles are written purely as reference only and your motorcycle may require different procedures. You should be mechanically inclined to carry out your own maintenance and we recommend you contact your mechanic prior to performing any type of work on your bike.
