Spark problem

Hi, my bike was working 100%. After standing for a couple of years the spark seems to be gone. If I remove the wire from the spark plug and touch the contact while turning the motor I get the electrical shock as per normal but if I connect a spark plug and earth the plug I get nothing. Any ideas where to start?
Would cleaning the points help? Regards Ewald

I just had exactly the same problem with mine yesterday after taking the bike apart and transporting it to my new flat. I've spent ages trying to start it and messing with the fuel before finding out that I had no spark at the plug. By holding the spark plug against the crankcase or exhaust pipe and cranking the engine over I get no spark, but when I hold the bare HT lead against the exhaust there is a nice spark! Conclusion is that the spark plug must be duff, sure enough when I checked it with my meter the damn thing is open circuit! So I've just ordered a new one and a new plug cap too just to make sure, hope it gets here soon.

Hi Vince,

I've changed both on mine but with no luck.

I'm thinking to check the earth and then the points and condenser.

Hold thumbs.

Hmmm, I've just got my new plug and cap and mine wont spark now either, it sparks fine when holding just the bare end of the HT lead against the exhaust though. My battery is a bit low but I dont think you need a fully charged battery to generate a spark but I'm going to charge it up anyway this weekend. I've got a good zero resistance earth connection between the engine and the frame and battery. I've also bought a new set of points and a condenser so when I pick up my flywheel puller this weekend I'll change those too. After that there's only the coil left!

Your battery isn't part of the ignition circuit, so that can't be the problem.

Hi, I found the problem. I cleaned the earth on the coil and all other contacts. After that I cleaned and set the points.
After that it started first kick.

Glad you found your problem, its good to hear that one of us is successful! I got my flywheel puller today and managed to get the flywheel off ok, then I replaced the condenser with a new one, same size and shape so it fitted fine. I soldered on the 3 attaching wires making sure not to overheat the thing in the process. Then I checked the continuity of all the wires from the condenser to the engine main electrical connector, all ok, also checked the contact breaker points resistance and continuity and made sure they open and close correctly with the flywheel back on, all fine! I removed the engine from the bike and removed the HT coil and cleaned the earth contact and then reassembled it back again. Then I put the bike back together and tried for a spark again by holding the spark plug up against the engine casing, but nothing. If I remove the spark plug cap and hold just the bare HT lead against the engine casing there is sometimes a faint yellow spark when I turn the engine over with the kick start. Reading up on Google this might be an indication of a knackered coil, Ive checked the primary coil resistance and its 1.7 ohms which is about what I expect, but the secondary coil gives no reading at all ( connecting the multimeter between the HT lead and the primary coil connection), I sort of expected a high resistance reading but it seems to be open circuit. So now I'm going for a new coil Hope this works (when it eventually arrives).

At last..... it starts! Eventually traced the fault to the HT lead where it enters the coil body, I gently pulled on it and the HT lead just fell out. New coil fitted and hey presto, a big juicy spark. Put it all back together and she started up just fine. Now I'm really looking forward to getting on the road for a run tomorrow evening after work.

Glad to hear you sorted it i had a electrical fault,took me most of the summer to trace down to the condenser + a few pounds later............

Got my first 5 miles under my belt this evening! She starts like a dream now, so no issues there and runs really sweet at idle and up to half throttle. When I first got her 6 weeks ago there was always fuel leaking out of the carb overflow and she was really rough at part throttle and wouldnt rev freely all the way even in neutral, so first things first I adjusted the float height so that there was less fuel in the float chamber and that really improved things, so much so that I had to turn the idle speed down quite a bit to stop her jerking when I engaged first gear. Now she runs really sweet at idle and initial pick up, the rough running is gone in the lower revs and now only detectable at half to max throttle. I've tried flicking the choke on a bit at higher revs but that just makes things worse so I'm thinking that there is too much fuel getting through at high throttle settings. I removed the air filter sponge and that made it a bit better which confirms my too much fuel theory. I've also checked the needle height in the throttle slide and its already set to the weakest setting, i.e. the circlip is in the top slot allowing the needle to drop to its lowest setting, moving the needle up one notch made it even worse. So now I've ordered a new Keyster kit from CMSNL to see if new jets and needle will sort it out. By the way my ST70 seems to have a C70 engine fitted and the carb looks to be the right one for a C70 from all the pics I've seen.