My ’82 is put away until next Spring, transfused with new oil and on battery life support, but with an unsolved issue that has me totally stumped. Motor is stock - 17,700 miles, cam chain tension and valve clearances all on spec, Keihin 34mm CVK carbs installed at end of June 2015 at 16,700 miles, jetted as shown in my signature and well-synched. I rode it about 700 miles this way with no problems before putting it away in late Oct 2015. Then since first 2016 startup in late April or early May (it always starts easily and and idles smoothly), it dies unexpectedly and unpredictably, sometimes backfiring, sometimes not, sometimes within a block to a mile of startup, while at other times, 5 – 10 miles or more down the road. Sometimes there’s a slight hesitation before it stops firing; sometimes not. I can re-start it quickly, usually while still rolling, by pulling in the clutch lever and hitting the starter button. Fortunately, I always made it back home, sometimes with just one such incident, sometimes with repeats. Switching the vacuum petcock levers to Prime made no difference, so my early troubleshooting focused on ignition.
First, I checked the clips that hold the ignition fuse. I had replaced all the original fuse clips in 2010 (the “Radio Shack” repair) - the replacement clips were all tight and the fuse was good. Then I completely removed the Boyer-Brandsen ignition system and went through all its wiring, inspecting insulation for any loose terminals, breaks or chafes, and cleaned and tightened ground and signal connections as needed, including the spark plug boots on their wires. I checked the timing advance at 3000 rpm; spot-on at 40 degrees BTDC. Voltmeter at road speed reads 14.2+ and does not sink before the bike suddenly dies. I have not replaced the plugs, since when it is running, it doesn’t miss a beat. On my first test ride after doing all this, it went 8-10 miles strong and smooth, enough for me to begin thinking it’s fixed, when it died like before. Attention then shifted to fuel supply.
I pulled the tank again and removed the two OEM petcocks to inspect their screens - both were intact, clean and in place. I checked tightness of all fasteners in the petcocks, tightening some a bit as needed, but did not disassemble them to see if they were blocked internally. Fuel flows freely through both petcocks with their levers in Prime position. I replaced the vacuum hoses for both petcocks with tight-fitting new ones. I pulled the CVK carbs; tightened the enricher assemblies in the carb bodies (one had vibrated quite loose); cleaned minor fine particles from bottoms of the bowls; removed, inspected and cleaned main and pilot jets (none were plugged); removed and cleaned (but did not re-install) the rail filter I had put in line below the T between the carbs; and replaced both bowl gaskets and both float needle valves with new Keihin ones. Both floats swing freely on their pins. I checked and set float heights to spec, then, after re-installing the carbs, checked fuel shutoff heights on both – one is dead on spec, the other within the +/- 1mm tolerance. Bowl vents are clear. I did not open the carb tops to inspect the diaphragms – I had checked them over before installing the CVKs and saw no visible pin holes or tears then. At this point, I’m out of ideas without even being able to isolate the problem to either fuel or ignition. All ideas welcome – it’s probably something pretty simple; I just haven’t been able to figure it out myself.
First, I checked the clips that hold the ignition fuse. I had replaced all the original fuse clips in 2010 (the “Radio Shack” repair) - the replacement clips were all tight and the fuse was good. Then I completely removed the Boyer-Brandsen ignition system and went through all its wiring, inspecting insulation for any loose terminals, breaks or chafes, and cleaned and tightened ground and signal connections as needed, including the spark plug boots on their wires. I checked the timing advance at 3000 rpm; spot-on at 40 degrees BTDC. Voltmeter at road speed reads 14.2+ and does not sink before the bike suddenly dies. I have not replaced the plugs, since when it is running, it doesn’t miss a beat. On my first test ride after doing all this, it went 8-10 miles strong and smooth, enough for me to begin thinking it’s fixed, when it died like before. Attention then shifted to fuel supply.
I pulled the tank again and removed the two OEM petcocks to inspect their screens - both were intact, clean and in place. I checked tightness of all fasteners in the petcocks, tightening some a bit as needed, but did not disassemble them to see if they were blocked internally. Fuel flows freely through both petcocks with their levers in Prime position. I replaced the vacuum hoses for both petcocks with tight-fitting new ones. I pulled the CVK carbs; tightened the enricher assemblies in the carb bodies (one had vibrated quite loose); cleaned minor fine particles from bottoms of the bowls; removed, inspected and cleaned main and pilot jets (none were plugged); removed and cleaned (but did not re-install) the rail filter I had put in line below the T between the carbs; and replaced both bowl gaskets and both float needle valves with new Keihin ones. Both floats swing freely on their pins. I checked and set float heights to spec, then, after re-installing the carbs, checked fuel shutoff heights on both – one is dead on spec, the other within the +/- 1mm tolerance. Bowl vents are clear. I did not open the carb tops to inspect the diaphragms – I had checked them over before installing the CVKs and saw no visible pin holes or tears then. At this point, I’m out of ideas without even being able to isolate the problem to either fuel or ignition. All ideas welcome – it’s probably something pretty simple; I just haven’t been able to figure it out myself.