What Nick says, I mostly use the stuff from S/S but have also used coils from Minimag. If you have not made the head yet then one of the smaller 1/4" rimfire Plugs or far eastern copies would suit that bore and give you a bit more room around the Valves

**LINK**

Hello Tom,

I don't know what you have purchased from Minimag, a Kettering system or Magneto. These should work first time. Bu if not, do yourself a favour and buy a modern model aircraft ignition system These work! I would further go on to say use either an optical switch or a magnetic sensor instead of points. These systems are cheap and reliable and while you are sorting out any problems (there usually are!) at least you can rule out the ignition part of the system.

If you want to use the old fashioned Kettering system and the 1930 / 40 model aircraft system then do so after all the problems are sorted . I use them all the time for my many ignition engines. I note some one says that the coil becomes saturated after a short time with primary current. This is bunkum and is perpetuated down the years. The coil reaches its maximum magnetic field for the given current, but the core is nowhere near being saturated. Apologies to the gent that claimed saturation, it is a common mistake.

If you have any problems, PM me, I think I have seen just about every failure mode for the small coil / capacitor type arrangement. Indeed I have made most of the common mistakes myself. Once sorted the old fashioned Kettering system is delightfully simple.

Regards,

Andrew.

The auto advance becomes more of a problem when people use them on 4-strokes and fit the sensor to the cam shaft so the unit thinks it is going twice as fast as it should.

Both Minimag and S/S units don't have auto advance though S/S do also sell ones with it for conversion of 2-stroke model engines where the sensor reads off the crank.

.

I think Duncan you only need 1 magnet. (providing it's a single cylinder) – If it's on the camshaft you will still have a wasted spark with a 4 stroke.

Edit :- Sorry that is wrong.! But you still only need one magnet. (providing it's a single cylinder)

Nick

Edited By Nick_G on 25/08/2017 10:51:44

The time when a wasted spark is an advantage is when a magneto is used. By driving the magneto at crankshaft speed, a higher voltage is attained than if at camshaft speed. For a coil and battery, no advantage, or disadvantage.

Ian S C

The modern aircraft ignition modules (maybe £20 or £30), have the option of 2 or 4 stroke ignition, Usually just a switch or a wire moved. An awful lot of big model aircraft are 4 stroke powered and the manufacturers cater for them in their modern units.

Don't get me wrong, I love the simple two stroke set ups of the 1940s, when set up they are very reliable. I thing that your supplier of minimags or whatever also sell the small spark plugs (that go into a glow thread). These Rimfire plugs are far superior to the old plugs. If it is a larger plug (I think they are 6mm thread?), make sure you get a reputable make, a lot of the cheap Chinese plugs can give problems. I think Bosch do them so no excuse for skimping on that item!

Best of luck with your experimenting. If you are using a magneto, then you are one up on me! When I tried to buy one, the guy was I think retiring? There obviously is someone new taking over the set up. I may even get to using a magneto after all. From a guy who made his own "They are not easy to make at this scale and you need to know exactly what you are doing". So I paid heed!

Andrew.