Hi all. Still working on my '81 SD900, Sprag bearing replaced and faulty starter motor identified, sigh...now, groan, despair: Both plugs out but in caps and resting on fins - Ign on and engine cranking - but - no sparks at plugs If I operate the Run/Kill switch while cranking a sole spark at each plug and the same when I return the switch to Run. I am aware the wiring from the primary side case is fragile and prone but before thinking "replace" what else can I check. Thanks.
If youb operate the kill switch without turning the engine do you still get the spark? If so I would be pointing a finger at the pickups or wiring
The Run/kill switch action is mimicking a single action of the points/whatever, so the coil is doing it's normal thing of reacting to the breaking of its 12V feed - hence the spark. I'd check the working and integrity of everything between the coil(s) and the Run/switch.
@ducv2 Yes, sparking when operating switch - engine still - and ign on, so it's a wiring check. @Keith_P Thanks, will do and post if/when sorted.
Well, not much to report but a slight situation change; as last post, spark still occurring when operating run/kill switch but this time only one way, that is:- Operate switch = spark, operate reverse = no spark. Before it was sparking when switch operated in both directions. To begin my wiring checks I removed the switch assembly from the bars and checked the wiring against the wiring diagram and it didn't appear correct so I re-soldered the wires, thus the slight change. The problem is still the same, no sparks when cranking engine, Ign on, plugs out connected and earthed and run/kill in either position. I have checked connections/earths/fuses and cussed a bit. (what a place to put a mass of wiring - in a bunch up under the steering head...you need to lie on the floor to see anything properly even with the tank off) It seems odd to me to lose both cylinders at the same time so what's common ? All I have done recently is work on the primary side with the cover off/on a couple of times - could I have broken BOTH pickup wires at the same time ? Everything else works, lights, horn etc. STOP PRESS: I may have answered my own question. I have just read in the manual "Fit the electronic ignition rotor, taking care to place it the right way round..." I am certain I did but... Could that be a reason for no spark at all, before I take the oil out again ?
With the coils disconnected from the 12V side of things, can you rotate the engine by hand and with a voltmeter, lamp, whatever on the to-coil lead to check if the 12V to the coil wire is transitioning from nominal 0V to 12V at the appropriate times? If so, your pickups are at least functioning.I Then check the coils by hand using a new plug, then yours, so you can narrow down your potential faulty components.... Do you fully understand how they produce sparks? Usual apologies here Also.... if everything is working and it's just the timing that's out, you'll still get sparks just not at the right time to make the bangs!
I have a rough idea of how it works like most but I do know that if the ramps on the ign rotor are not passing under the pick-up coils then nothing will happen. No apologies necessary as electrics were more easily understood when I was much younger
The ign rotor is on correctly - I can see it with the primary side top cover removed so at least that's another thing checked out. Strange and perhaps significant to me to lose both sparks at the same time though.
Haha, yes, I agree - much easier when you could actually see points opening & check when by using a fag paper! Keep isolating & testing if you can. My bet it's something really basic - here's hoping
Just finished studying a physical picture and a wiring diagram of the Ign system and of course the one thing in common is 12v so I’ll make sure I have that from the battery through to the electronic loom next step. Kill switch duff maybe, here’s hoping.
Apologies for not finishing my thread. Whist sitting on my stool just staring at the engine and wondering, like you do, my eyes fell on the zip-tie securing the pick-up wires from the clutch cover to the frame. How tidy they were and I remembered moving them while I was working in the at area to keep them as far from the heat of the exhaust pipe as possible, so I put them back to where they were (just moved them around the frame a little) and tried again - Bingo. Stripped the insulation cover back and exposed 4 single wires with insulation completely de-composed and green moldy looking wires. All four wires were replaced one at a time from the pick-ups to the loom and job done. well it is 40yrs old...
Just to wind up the thread. I didn't take up DP's offer to try exchange bits, which was very biker friendly of him to propse. I eventually took the motor to an Industrial electric motor specialist and asked could they help. They had a division which dealt with small motors and mine was duly accepted for service, sent off and came back working correctly.
Hi. No, it’s a Darmah SD900 but personalised by me which included the frame colour change. I was heavily influenced by everything I saw at the Duke Owners meets in the Island, early 80’s. The Darmah is after all a roadster and I grew up in an age of “clip on’s, rear set’s and swept back exhausts” .
