SERIOUS MISFIRE PROBLEM

[trophy]

The last two runs I have been on my 1962 model 31 (12v negative earth) developed a serious misfire after approx 30 miles, this cleared up relatively quickly. On both occasions I carried out the usual checks and found nothing obvious, however I'm no electrical genius. Last year I replaced the distributor points and condenser with a Powerspark electronic ignition unit and am very pleased with it. Should I suspect the unit?

[g80csp11]

most times it will be a low battery voltage /charging problem
if volts drop too low on most electronic systems the timing shifts

[trophy]

Thanks Peter. I ride with 21w qh running light and will keep your advice in mind next time out. Cheers.

[Reynard24]

I doubt that battery voltage would play a part in varying the timing as the Powerspark retains the manual advance/retard in the distributor and simply provides a firing pulse for the coil. Have you used copper HT leads? The carbon ones can break down. Check the dizzy cap, carbon brush and rotor arm are also in good condition. I'd also check that the firing magnet collar that fits on the cam is fully pushed home along with the rotor arm. I've used two of these on dizzy equipped bikes and they have been much better than points and condenser.

[trophy]

I doubt that battery voltage would play a part in varying the timing as the Powerspark retains the manual advance/retard in the distributor and simply provides a firing pulse for the coil. Have you used copper HT leads? The carbon ones can break down. Check the dizzy cap, carbon brush and rotor arm are also in good condition. I'd also check that the firing magnet collar that fits on the cam is fully pushed home along with the rotor arm. I've used two of these on dizzy equipped bikes and they have been much better than points and condenser.

Hello Reynard24. I too like the Powerspark system and have had no trouble in more than 1000 miles, until now. I use copper HT leads together with NGK's resistor caps. As you suggest I will check the firing collar is fully home. As for the rotor arm, together with the carbon brush and condenser these are on my shelf as the Powerspark system makes them redundant. Don't they If the problem continues I will refit the original dizzy system and see what happens.

[TrevorCSR]

Going back to the original post, it's very unlikely there's anything wrong with your electronic spark unit. I'd look elsewhere. Electrical connections? Carburation? Fuel supply? You say 'this cleared up relatively quickly'. What do you mean by that? Did you stop for a long time and re-started and all fine until another 30 miles down the road?

[Reynard24]

If you are using a twin output coil you won't need the rotor arm. I use a single coil so still use the rotor arm and have had no problems in over 4000 miles. I don't think it will be electronics causing the trouble - the system doesn't lend itself to be intermittent I'd have thought it would either work or fail completely but it is fairly simple just to refit the original setup just in case and retest.

[trophy]

Thanks Reynard 24. Yes ,I am using a twin output coil, A good one from my previous Honda CD175. Trevor CSR I have checked the wiring and connections. Completely rewired, + new battery 1500 miles ago, also fitted new carburetor from the club at the same time and the carb checked out fine after both faulty runs. The problem happened on two separate runs. 30 miles into each run. It spit and f****d, fired out of step and a few big bangs from the silencer. The it just cleared up and ran right as rain. I hadn't stopped, just coaxed it along for 2 to 3 minutes when it cleared up, same on both runs. Am still baffled.

[g80csp11]

just had a thought , on my P11 the lucas pattern ignition switch has caused issues with high resistance and low voltage
it used to run for a couple of miles , miss or stop . when I turned on and off the ignition all was fine
the problem was corroded contacts in the ignition switch

may to bypass the ignition switch and see if the cures the problem

dogged me for ages until I found the problem

[trophy]

just had a thought , on my P11 the lucas pattern ignition switch has caused issues with high resistance and low voltage
it used to run for a couple of miles , miss or stop . when I turned on and off the ignition all was fine
the problem was corroded contacts in the ignition switch

may to bypass the ignition switch and see if the cures the problem

dogged me for ages until I found the problem

Thanks for that. Next time out I will give it a go and report back.