Reply To: Oxford Allen Scythe Villiers Mk25c

[sidevalve5]

Hi Dave,

Had another idea that may solve your problem. If the HT and LT continuity tests are fine, you could fit an external Meco transistor ignition unit. If you can get to the wire terminal on the hot side of the points, you could disconnect them and connect with a wire fed from the Meco unit though the back of the armature plate. The Meco module dispenses with the points and condenser. It works by ‘sensing’ flux reversal when the flywheel magnet passes from north to south over the coil’s soft iron core. This is when the points would start to open, the Meco unit has a transistor that does the same action. Namely stopping the flow of electric current to the primary windings. Because this action is so much faster, the collapse in the magnetic field is quicker too, resulting in a bigger spark at the plug.

The above is the theory, I have not fitting one myself. Although I had a duff coil on a Briggs & Stratton, it had a points system. I replaced it with a new modern ignition module and the spark exceeded the 6mm gap I like to achieve. Have tested other engines for spark gaps with these modules and >6mm is the norm. The Meco is available on ebay at £10.09p and for that money, it may be worth a punt. Have both a Villiers Mk25c on the Clifford and a Jap 2a on a Colwood that I have not used for a couple of years. Will get them out this spring and test the spark gap, if <6mm will fit a Meco unit just out of curiosity.

To test your coil with a multimeter, ground the black lead, set to 20K and put the red probe in the plug cap to test for HT continuity. For the primary coil, set to 200, put the probes together and note the reading, it may be a fraction of an ohm. Disconnect the points and put the red probe on the wire that goes to the coil. From the reading, deduct the figure that was noted with the probes together.

Another test that I have not personally done is to get a 6v or 9v battery. Set up a spark tester, or if you cannot get hold of one. Remove the earthing electrode from an old spark plug, if this sparks the gap is about 4mm. Clip a wire from the negative terminal on the battery to the armature plate, ensure the points are closed and with a probe from the positive battery terminal, quickly tap the screw on the points that retains the terminal for the wire that goes to the coil. This test ‘loads up’ the coil so is a test that better replicates performance when the engine is rotating. But I would still do the multimeter test first, its recommended by engine manufactures, including Villiers.

Of course even by fitting the Meco unit, the flywheel will still be stuck on the crankshaft and you will still have the same problem if the coil fails. You could do as you suggested originally and try to get the points serviceable with the flywheel in place. Then mount an external battery, coil and condenser. To get the flywheel off you may try to adapt an existing three bolt puller and tap holes in the flywheel spokes. If you do get it off, you could reuse it by turning the nut retaining section and using a new nut on the crankshaft. Or if a replacement flywheel is readily available, cut if off like Andy says.

Grahame