I've been plagued for almost a year now trying to sort out why my #2 cylinder wouldn't fire. Everything I tested checked out. Spark seemed fine. Voltages at ignition coils is fine. Voltage along the entire circuitry is great. Compression on all cylinders is fine. Balanced the carbs with vacuum gauges within a couple mmHg. Cleaned the carbs. Checked the float height in the carbs. Ran ethanol free fuel. Valve clearances are all in spec. Points/timing all adjusted and in spec. Timing chain checked and double checked while replacing valve seals. Checked for vacuum leaks at carb boots. Should I go on? I bugged many of you over the past year searching for solutions and possible causes and you were all very willing to help (thank you!). But I've finally found what I believe to be the cause!!
:drumroll:.........the accelerator pump diaphragm (specifically, the vacuum sensor) was trashed. That was it. I took it apart and it was completely porous. I bought a rebuild kit and after installing and testing, not only did all four exhaust headers heat up to within 10 deg F but after a quick test ride it sounded beautiful and it pulls when you hit the throttle!! It idles correctly and everything! It's a miracle!
So, the morale of the story is to check your accelerator pump diaphragms if you have issues with the cylinder that the pump is on. Hopefully this saves someone else a year of stressing and frustration. The good news is that I now know how to diagnose basically every part of the ignition on my bike.
1980 KZ650F1 - 10k miles (see photo)
1981 KZ305 CSR - 10k miles (didn't have the heart to customize this one, will stay original)
