Troubleshooting a Motorcycle


Recently, a reader requested an explanation of how to troubleshoot motorcycle problems for the DIYer. That’s a tall order. After 25 years of fixing bikes, l have an experience base to know where to start with a few simple checks.

But this doesn’t help the guy working in the garage on his own bike, who normally grinds a 9-5 desk job. To gain some perspective, I teach students and instructors troubleshooting methods at the Motorcycle Mechanics Institute in Phoenix and Orlando. Before I train students troubleshooting in factory elective courses, they have already been through 36 weeks, five hours a day, of core training. Instructors have 5-40 years of shop experience and potentially hundreds of hours of factory training. Even the instructors are occasionally stumped by problems.

Troubleshooting woes aren’t limited to motorsports. I’ve paid thousands of dollars to have my wife’s car fixed, only to find out they were misdiagnosing the problem and charging me to replace perfectly good parts at a well-known automotive dealership. While I can’t give you the thousand words, that represent the thousand pictures in my mind of thousands of experiences, I can give you basic tools to start the learning process and gain your own encyclopedia of troubleshooting knowledge. The process requires research of the systems, but over time, most can learn to be effective troubleshooters.

The key is to use a systematic approach. Categorize the systems, isolate the problem and bypass or verify the problem. Categorizing Systems Machines and devices can be categorized by systems. A desk lamp could be broken down into wire-harness, frame and bulb. A motorcycle is more complicated, with chassis, engine, ignition, charging and fuel systems. Each system has sub-categories. A charging system has a stator, regulator- rectifier and battery.

By categorizing the components or system, we can better isolate the problem, which is the second step to troubleshooting. As we determine which major system is the problem, we can then subcategorize and narrow down the results to more isolated locations until we find the source. Isolating Problems Let’s say the desk lamp light won’t turn on. Being a simple system, most of the issues can be checked through audial or visual inspections. I look down to see if the lamp is plugged in. It is, so I check the switch. It’s in the on position and makes a click when turned off and on. I don’t want to pull out the volt meter to check yet so I move onto checking the bulb. It is frosted and I can’t see inside, so I gently shake the bulb and hear rattling inside. I assume the filament is damaged. Why didn’t I check the switch? Financial investment and experience. Time is money and it’s a waste of time checking things that aren’t broken. I can check the bulb much quicker than testing the switch. Experience tells me that most of the time the bulb is the weak link.

While more complicated, vehicles can be checked similarly. If, for instance, the bike doesn’t start, but it cranks, I could assume I have power, but it may not be enough. After checking the battery with a volt meter, I find 13 VDC, which is plenty. It drops down to 12 VDC when turning over, indicating a strong battery. Since the bike turns over, I know the starting system works. I tested a well-charged battery, so I know the charging system works. This tells me I need to isolate further checks to the engine, ignition and fuel systems. Of course, this requires an understanding of power flow. Engines have a linear power flow from piston to rod, to crank, to primary gear, to clutch to transmission-input to transmission-output. Electrical is always a loop that starts at a power source and typically has a fuse, switch, load and flows back to the power source to complete the circuit.

Fuel starts at a fuel cell, and is pumped or gravity fed through a fuel line to the carburetor or injector system to deliver fuel and air to the engine. Each of these systems has a flow direction from one point to another. If we find out at which point the flow stops, we find the problem or a symptom of it. Most service manuals use flow charts to help technicians walk through the flow in order to find the root problem. To minimize time investment, I start checks somewhere in the middle of the flowchart when possible. It’s called “Divide and Conquer.” If the components are good up to this point, then I know the issue is further in the fl ow. If the mid-point is not working, I know the problem is somewhere before. This will isolate where the problem is located and cuts my diagnostic time in half when the problem exists at the end of the circuit.

One of the things you can do to help yourself understand a system is make your own fl ow chart. Identify the parts and fl ow of power then write them down in a fl ow chart with arrows indicating direction of power fl ow. In electrical training, we call these block diagrams, but it could be used just as well with mechanical items. Once you get more familiar with the system, the block diagram becomes less important for understanding, but is nice for writing notes as you take steps to diagnose the problem. Power train fl owcharts are simple. Wire diagrams can be very complex with multiple pathways to check. Even the experienced technician can get lost in the weeds when troubleshooting electrical systems. They may create simplifi ed block diagrams to keep them on track.

BYPASSING OR VERIFYING THE PROBLEM Once I’ve isolated the problem, I take steps to verify. If I have a “known good part”, I can install it and see if it works. But if there was another problem that caused the component to fail, I may be turning a “known good part” into another failed part. I prefer to bypass the component or circuit to test the source. If my clutch cable was binding internally, I would feel excessive resistance at the lever. I disconnect the cable and the lever feels fi ne. Next, I would disconnect the cable from the clutch disengagement mechanism and try the cable by itself. This is one way of bypassing the circuit and checking the component. The inverse of this is bypass the component. If I believe an electrical switch is preventing a light from turning on, I simply bypass the switch by connecting power across the switch with a wire. If the light turns on then it reinforces that the switch was the problem.

SYSTEMATICAL APPROACH When working on bikes and ATV’s I start by separating the machine into mechanical, electrical and fuel components. Then I go about checking each one with simple tests that operate functions of the vehicle. If the electrical is in question, I turn on the key and see if the lights turn on. I try turning the starter motor as well. I turn on the key and listen for electronic servo motors actuating throttle bodies and fuel pumps whining. I check battery power with the key off, on and running. Mechanically, I’ll check the feel of brake and clutch levers. I roll the bike back and forth in gear with the clutch disengaged. Then do the same in neutral and each gear but with the clutch engaged. I compress the suspension and feel for smooth operation and noises. For fuel, I’ll try starting the bike and listening to how it’s running. Is it backfi ring/misfi ring or running hot, (lean)? Is it running cold, blubbering or eight-stroking (rich)? I’ll open the gas tank and listen for air escaping or sucking-in, which could indicate hydraulic lock or venting problems. On fuel pumps, I’d check fuel volume over time and fuel pressure indicating proper volume and fl ow. Each of these simple checks take seconds or minutes, but answers multitudes of questions. Experience will tell you what to check and how to check it. Your solutions will come quicker as you expand your knowledge base. I didn’t get formal training when I went into this fi eld. I picked up a service manual and just did what it said. Lo and behold, most of the time it worked. You know what I found when reading manuals from different manufacturers? Just about every manufacturer followed the same principle: Use a systematical approach, categorize the systems, isolate the problem and verify the problem. I don’t consider myself a rocket scientist and I struggled with many concepts along the way. Perseverance was my friend. If I can do it, I think most people could do the same. If you don’t have the time or patience to learn these techniques then you can always support the cause by having your local dealer help you out.


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