SOHC.co.uk Forums > CB350/400
No ignition sparks at the plugs
Gary400/4:
Thanks for the input. I am still non the wiser. The points are still serviceable given that they are gapped and the fibre heels mean that they are still within adjustment to time the moment when the points to the F1-4 and F2-3 marks start to open. The blue wire is paired to coil serving cylinders 1-4 and corresponding set of points. Conversely the yellow one serves the coil to cylinders 2 and 3. The black and white wire which carries ignition voltage common to both coils. The black wire within the loom is a positive supply to all of the ancillary components. Because continuity exists between live and ground via the resistance of bulbs in the console, there are 3 common green ground wires between hi beam and the indicators. I am wondering if this is causing me to detect this at the points? I have seen replacement coils for the FL703 on eBay at around £25 each. They are push fit HT leads with screw locking caps.
Should I be detecting continuity of around 7 ohms between the points terminal wire and ground when the points are open or should this be closer to infinity? To know for sure will help me with my investigation.
Lobo:
There are many possible points of corrosion in the ignition circuit, and as a first port of call you might try hot-wiring the coils directly to the +ve of the battery.... ie cut out the ignition switch, kill switch, and old wiring / bullets in the original feed. Of course, also ensure the points back plate is securely earthed. If this solves your problem you’ll then have to work backwards checking the aforementioned components in turn.
Moorey:
Welcome to the forum. I see your already having fun. ;)
Lobo:
... at some point today I’ll measure the resistance figure you seek on my (working!) 400F.
Addendum... Doh, and sorry Gary, my 400F has a breakerless ignition, and to get what you want would mean a fair bit of disturbing things. My excuse is 7am writings and 5 different bikes... forgive me!
I agree the ‘idiot’ lights would induce a reading, but don’t forget that the test you describe will also include the respective coil primary winding and the voltage regulator resistances. (The VR, I think, will be feeding the alternator field coil at 0 rpm. (My ‘750 book suggests this field coil is rated at 7 Ohms & I’d guess the 400F same-same). Anyways, point is, if you disconnect the Regulator, take out the Oil Pressure lamp, put the bike in gear (Neutral lamp out), all lights off etc... then your yellow / blue test circuits should only be measuring their respective Primary coil resistances. And if these 2 values (ie Yellow & Blue) are the same, then that’s a good sign.....though not proof of a healthy ignition system.
I still reckon your best staring point is as per my earlier post; for my money the culprit might be the kill switch which has weeny contacts, carries a couple of amps, is prone to water ingress, and whose loom is always on the move.
mike the bike:
In other words.... have you got 12V on the black/white wire going to the coils?
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