New Magneto Thread help needed

[Swarfcut]

  Bob..   The fact that the bike starts and runs with the old magneto would indicate that the engine is basically sound mechanically.  The refurbished replacement magneto is not up to the job for some reason.

   But with the supplier willing to give a refund, this leaves the scene and we are back to the start. Andrew's offer of a short term loan would prove if the fault resides within the fuel system. I have every faith in his reputation, and feel sure that he will assist with practical advice as well if necessary.

  The number one problem with an old temperamental magneto is the fragile and penny pinching electrolytic capacitor (Condenser) buried within the armature.  The symptoms you have of  good cold starting then later failure would be a pointer to a problem here.
 
  These days there is a cost effective solution from Brightspark Magnetos, which is another avenue to consider if you want to stick with old school ignition rather than moving to electronic, such as  the Thorspark system which employs the duff magneto as a carrier, using what you already have and in the grand scheme of things is a reasonable choice.

 Swarfy.

[Rex]

"Penny-pinching electrolytic capacitor"?
It's lasted 60 years, so how much longer should it be expected to go on working for?
Another vote for the Bright Spark replacement capacitor (I have them on three of the fleet) but wasn't keen on the Thorspark set-up although many seem to find it works great.

[CheeserBeezer]

Hi Bob, I feel your frustration. I don't know where you are in the UK but, if you were round the corner, I'd bring a mag, fit it for you (in about 40 minutes), and send you off over the horizon with a smile on your face. It is often the case with old bikes, and in life generally, when something goes wrong we solve the problem by circumnavigating it (electronic ignition = divorce) rather than persevering. Going down different avenue (remarriage?, though thankfully I don't speak from my own experience!) only brings about a different set of problems. The original design of the A10 worked well for those who looked after their bikes (changed the oil = bought them flowers) and it is difficult to improve on what the manufacturer did in the day. If your mag supplier is refunding you  then you can buy one of mine....which will be cheaper.... and it will work....and if it doesn't I will personally come and fit another until you are 100% happy.

[trevinoz]

That must be the deal of the century, Andrew.
Well done.

[Slymo]

I'd definitely replace the spark plugs. Modern unleaded gas produces a very fine and highly conductive carbon when it fouls. I've put plugs on a mains powered megger and had them produce a bright white light as the carbon burnt off. Not good for the megger probably but interesting as the plugs looked completely clean but were giving a very uneven performance in the bike. Two mags with the same result would tend to suggest the problem lies elsewhere. I had a fault plug cap that caused a similar problem once that I only spotted when running the bike at night.

[RDfella]

Speaking of plug caps, remember we shouldn't use resistor caps (which most are these days) on a mag sparked bike. I posted a while back the figures of how they beat up a mag - here's a copy. Believe is was from Brightspark. Note how they reduce the spark and increase voltage in the mag.

                                                                     without suppressor                with 4.6kO suppressor                   difference
peak voltage to initiate spark                                9,600V                                  10,600V @ magneto   
                                                                                                                 9,300V at plug                             -3.10%
DC component of HT current after striking spark         53 mA                              52mA                                     -1.80%
DC component of HT voltage after striking spark          910V                             1,160V at magneto                     27.30%

[berger]

i once used supressed plug caps but didn't know they were until a chap told me to get them off and sod upsetting the neighbours tv's i took them off the next day and found out they could damage maggy

[bikerbob]

 I contacted Andrew at Priory Magnetos and sent my mag off to him he rang me to say that there were problems with it namely the armature had been rewound before but it was an amtuerish job and the capaciotor was of a type that has not been used for some years because they were not reliable and one of the pick up brushes was too soft. he refurbished the mag it is now fitted to the bike and it now runs perfectly. So if anyone has a mag problem they can do no better than to contact Prory Magnetos they will get first class advice and an excellent job done.

[CheeserBeezer]

Very kind remarks. Thanks, Bob.