Excellent engine stability is even when completely cold. The mechanical noise was low for its age, and the motorcycle was running great right from the start. However, after about 10 runs, when the engine was warmed up properly, it started to blow slowly, causing a one-lung symptom and making it impossible to run the motorcycle properly.
At first, I thought the engine ran out of gas! but it didn't look like that. Then I suspected the ignition system.
Ignitor? IG Coil! ? Or...
After warming up the engine, a trial run was started. However, after about 10 minutes of running, the engine goes into one lung. Is it the ignition coil? Is it the igniter (transistor ignition unit)? Or is it the pickup coil? We replaced it with an unbroken igniter, which can be easily checked by turning on the coupler, and test-drove the motorcycle under the same conditions. However, the same one-lung condition occurred, so we decided that the igniter was not defective.
Something is wrong with the pickup coil.
Troubleshooting resumes with a part that can be replaced more easily than the ignition coil. The igniter unit in the right side cover at the crankshaft end can be used for other models in the series as long as the coupler shape matches.
The engine malfunctioned, so we returned to the garage. However, by the time we do maintenance, the engine has cooled down. The trouble symptoms disappear.
At this stage, is it the IG coil or the pickup? I figured that one of them was definitely the cause of the trouble.
I drove around in circles on the roads around my house and immediately returned to the garage to check the suspicious parts with a tester when they became erratic.
It turned out that while pickup 1/4 had the specified resistance, pickup 2/3 had no resistance, in other words, a broken wire! It was also found that there was no continuity in the No. 2/3 pickup when it was warm, and then when it cooled down, it returned to the specified value of 0.4 to 0.5 KΩ.
This is tough trouble to solve. I had no choice but to borrow a used pickup coil from a motorcycle store I know and replaced only the No. 2/3 pickup.
Trying it out on borrowed parts.
The maintenance vehicle is an export-spec Z550GP with pickup coils for No. 1/4 and No. 2/3 respectively. The borrowed pickup coil was for a Japan model Z400GP. I borrowed a live coil for No. 2/3, but the harness was cut, so I pulled out the wiring connector terminal from the connection coupler with a special tool and soldered the wiring to restore it. When removing the terminal from the coupler, it would be troublesome if the position is wrong when restoring, so it is better to take a picture of the positional relationship with a smartphone before disassembling it.
Converted to enhanced ignition system in the future
Most of the problems with old motorcycles are electrical, and especially common are problems with the charging system and the ignition system. This time, a simple investigation of the cause and replacement of parts enabled the motorcycle to ride normally, but in the future, we hope to make the motorcycle free of ignition system problems by constructing a new ignition system. One such special ignition system part that has received extremely high praise is the SP II Full Power Kit developed and sold by AS Uotani. Unfortunately, there was no kit lineup for the 1981 Z550GP, so we will try to install the Full Power Kit by diverting kit parts for the Kawasaki Zephyr and Zephyr χ with the same series engine. The same method can be used to strengthen the ignition system for the Japan-spec Kawasaki Z400FX.
POINT
Point 1 - Clear determination of malfunctioning conditions & symptoms
Point 2 - Circuit tester with visible electricity flow
Point 3 - Sometimes a simple unit replacement can be a pleasant experience.
The vehicle's inspection had already expired when we purchased it, and since then we have been enjoying nightly customization and maintenance of the 1981 Kawasaki Z550GP, an export model while pursuing ideals such as "pursuit of my own specifications. Six months after purchasing the motorcycle, the bodywork had been polished to a reasonable shape, and it was time to take it for a test drive. So, I made an appointment for a user inspection, and it passed the inspection.
Now that the cost of liability insurance is lower than it used to be, the cost of a two-year continuous inspection is only 20,000 yen or more! Since we ask a substitute document preparer to prepare the inspection documents for us, we could have done it cheaper if we wanted to, but it would be a hassle to make a mistake in document preparation.
By the way, whether it is a Japan motorcycle or a foreign motorcycle, the cost for a 2-year continuous inspection is almost the same.
The day after obtaining the inspection, we installed the license plate number, warmed up the motorcycle thoroughly, and started test driving. There is a gas station about 10 minutes from my house that I have been going to, so I first drove there to fill up with gas. After refueling, I started the engine. As soon as I started running, the one-lung symptom occurred. I stopped at the side of the road and touched the exhaust pipe with my hand, and it seemed that No. 2/3 was not burning. If only one cylinder was not burning, I could suspect the plug, plug cap, or high-tension cord, but if 2/3 of the cylinders were not burning, the cause must be in the ignition system.
I went back to the garage, took off my helmet, and after doing my business, started the engine again. Huh! The engine blows up as if nothing had happened. I had no choice but to go out for another test run, and this time the same symptom occurred within a minute of riding. I immediately went back to the garage to check the spark and found that the #2/3 IG coil was not burning. I replaced the No. 2/3 IG coil ignition signal terminal with the terminal of the No. 1/4 coil, and this time the No. 1/4 plug stopped firing. I decided that this was a complete ignition system problem.
Later, when we investigated the cause, we found that the trouble was in the No. 2/3 pickup coil (Kawasaki named it a pulsar coil at that time). Measuring the resistance between the two harnesses, we found that the resistance of the No. 1/4 pickup was always 0.4 to 0.5 kilo-ohm, while that of the No. 2/3 pickup was 0.4 to 0.5 kilo-ohm when cold, but when the engine was warmed up and the heat was transferred to the coil, we found that there was zero continuity or disconnection.
As it turned out, after replacing the coil with an unbroken pickup coil, the motorcycle was able to continue running normally after that. During the troubleshooting, I checked the difference in ignition spark between the vehicle and the one that had AS Uotani's full power kit built in, using a spark plug. I was astonished at the difference in the thickness and power of the spark. This definitely has an effect. I am very much interested in installing this kit.