Stumped!

aldo5468

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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.
 
I had that experience with a Boyer Micro Power ignition years ago; the problem vanished when I removed the Micro Power igniter box and 0.6 ohm Gill coil and reinstalled an older Micro Digital igniter box and Dyna 5 ohm coil (timing plate is the same in both systems.) The symptoms were the same as yours: sudden engine failure followed by immediate start-up. Maybe someone here has troubleshooting specs for the MP box; you won't find anything useful on the Boyer site.
 
removed and cleaned (but did not re-install) the rail filter I had put in line below the T between the carbs .

Your statement above bothers me, or maybe I'm not understanding. Does your fuel line go beneath the carb inlet/s and then up again ? Fuel lines should be short, downhill and never uphill, unless you're using a fuel pump.

Scott
 
It does sound electrical and Griz may be right about it being something related to a Boyer. Do you have another ignition available to try, even reverting back to stock (for testing) if need be? If that's not it, it may be somewhere in the power feed to the ignition, like the key switch or kill switch.
 
Hi,

I've used the Boyer ignition on quite a few bikes now. Ive had two problems, like yours and here's my tuppence worth:

1. Ignition switch (aftermarket) came loose inside and depnding on where the key hung, it would cut out and splutter to a stop. When any testing was done, spark and fuel appeared correctly - just a process of elimination

2. This one sounds more like your issue - Plug leads. This was also on an XS. They looked perfect with no signs of wear and were only 10 months old. The bike would start first / second kick and run for 2 - 5 miles then start cutting out then die. Give it 5 minutes and it would start right back up. I tried various checks as you have done, swapping the leads for newly made ones as a last resort - result. I even put the old leads back on to prove it and it conked out again.

Hope this helps
 
Also check your running voltage - Boyers are very fussy on what they will run on -They must have a fully charged battery in good condition and your charging system must be providing the correct voltage. I've found anything less than 11.5v remaining and the Boyer will take the huff
 
Your statement above bothers me, or maybe I'm not understanding. Does your fuel line go beneath the carb inlet/s and then up again ? Fuel lines should be short, downhill and never uphill, unless you're using a fuel pump.

Scott
I have two T's, an upper one needed to connect the two petcocks and the lower one that's part of the EX500 carb assembly. The upper T (the one I was referencing in my original post) is inline horizontally with the petcock fuel outlets, above the carbs, and aligned vertically with the lower T below that feeds into the carbs.
 
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It does sound electrical and Griz may be right about it being something related to a Boyer. Do you have another ignition available to try, even reverting back to stock (for testing) if need be? If that's not it, it may be somewhere in the power feed to the ignition, like the key switch or kill switch.
Now wish I still had the original TCI to try what you suggest - unfortunately, I passed it along several years back when I got the B-B unit.
 
Hi,

I've used the Boyer ignition on quite a few bikes now. Ive had two problems, like yours and here's my tuppence worth:

1. Ignition switch (aftermarket) came loose inside and depnding on where the key hung, it would cut out and splutter to a stop. When any testing was done, spark and fuel appeared correctly - just a process of elimination

2. This one sounds more like your issue - Plug leads. This was also on an XS. They looked perfect with no signs of wear and were only 10 months old. The bike would start first / second kick and run for 2 - 5 miles then start cutting out then die. Give it 5 minutes and it would start right back up. I tried various checks as you have done, swapping the leads for newly made ones as a last resort - result. I even put the old leads back on to prove it and it conked out again.

Hope this helps
Replacing the plug leads sounds like the next thing to try next Spring - thanx for sharing your experience.
 
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