These motors have a CD box and single coil feeding a mechanical distributor under the flywheel. Timing is by a double-contact point setup. The components are hard to obtain, hard to access for service, and very expensive.

Of course this is a two-cycle engine so each plug fires once per revolution, but a "waste spark" setup would not be ideal.

My idea is to use 4 "coil-near-plug" "smart" coils (meaning the driver transistor is built into the coil). They could be separate coils or built into a "block." (Something like this: https://www.amazon.com/339-879984a1...coding=UTF8&psc=1&refRID=28V8QVZTVVFY1M3FDA5X) I would drive them with with 4 sets of contact points mounted at 90 degrees--each point set controlling one coil. ( I have seen this point-set-for-each-cylinder as a factory setup on old West Bend outboards.)

This sort of coil usually uses 5V (ttl?) signalling. I'm not entirely sure how best to drive the coils from contact points. (They would be fire-on-open). Can anyone advise on this, or point out problems I'm missing? Thanks!

 

Can you elaborate why a waste spark is "not ideal?" It's simple and quite often used. If the RPM is extremely high (as with some small model engines) getting the capacitor charged in time can be a problem. What other issues are you concerned about?

 

This sort of coil usually uses 5V (ttl?) signalling.

Is it logic high (5V) or logic low (0V) which fires the coil?
Would you still be using the CD box?

 

Can you elaborate why a waste spark is "not ideal?" It's simple and quite often used. If the RPM is extremely high (as with some small model engines) getting the capacitor charged in time can be a problem. What other issues are you concerned about?

In some engines, a waste spark can ignite the remains of incomplete combustion while the valves are open which is hard on intake and exhaust components. Awhile back there were a few waste-spark electronic ignition systems installed on experimental aircraft O-360 Lycomings. Those engines also had 'new and improved!' lightweight Ryton plastic oil sumps through which the induction air tubes passed. Aircraft engines are frequently started with excess fuel present. When the waste-spark fired off with the intakes open, it would blow the oil sump right off the engine. So, there's that.

 

Consider that this is a 4 cylinder 2-cycle engine that fires every cylinder every revolution, and the cylinders are exhausted by mixture pumped through the crankcase. Is there a place in this scenario for pairs of plugs to fire together? Maybe there is: with each cylinder firing every 360 deg, that's a cylinder every 90 deg, or 2 cylinders every 180 deg. I need to play around this this. But, there are plenty of systems using a separate coil for each plug.

I would not anticipate using the CD box. Believe the coils fire on high, whereas the point controlled system fires on contact break. Hmmmm.

 

Believe the coils fire on high, whereas the point controlled system fires on contact break. Hmmmm.

Easily handled with logic inversion if necessary, but it helps the design process to know .

 

Consider that this is a 4 cylinder 2-cycle engine that fires every cylinder every revolution, and the cylinders are exhausted by mixture pumped through the crankcase. Is there a place in this scenario for pairs of plugs to fire together? Maybe there is: with each cylinder firing every 360 deg, that's a cylinder every 90 deg, or 2 cylinders every 180 deg. I need to play around this this. But, there are plenty of systems using a separate coil for each plug.

I would not anticipate using the CD box. Believe the coils fire on high, whereas the point controlled system fires on contact break. Hmmmm.

My original comment was just for more information, not a suggestion per se. Wasted spark is quite common even with 2-stroke engines (see several Yamaha engines). With twin cylinders it is quite easy to do. With 4-cylinders in a boxer configuration (i.e., 180° apart firing, two cylinders at a time), it is still quite easy. With 90° firing, it would be more difficult as you note.

I didn't do a thorough search, but here is one link to a discussion of wasted spark in which Yamaha is mentioned: http://www.yamahaoutboardparts.com/...-outboard-forum/25544-two-stroke-wasted-spark . Ignore the usual blog banter. There are other discussions about the matter of crankcase compression and exhaust. That boils down to timing in boxer engines.

Maybe a two-point waste-spark system would be easier to implement than a 4-point system with your engine. I don't know. My experience is with boxer style.

I am clueless about how difficult getting current mechanical parts to fit on that engine would be. Many years ago, I did an engine swap in a late model fuel-injected car. Salvage yards were a life saver for finding parts that could be modified to fit.

 

Thanks for this helpful information! I have assumed that when the piston is at bottom dead center there would be ignitable mixture flowing in the top of the cylinder.... Maybe not. I doubt that ignition at that point would be healthy for the reed valves, crank seals, etc. Maybe not? I have little experience with complex 2-stroke engines. My main objective is to get rid of the mechanical distributor, and I'd like to come up with a scheme not requiring a lot of machine work. People are scrapping these motors because of ignition issues.

So, I've been looking for a coil block, or pack, with 4 independent coils and the switching transistor built in (a "smart" coil.) Or, individual coils could work. Seems hard to find specs and schematics on line.

This one? https://www.google.com/search?q=UF-...0KHesvB_sQ9QEwA3oECAcQCQ#imgrc=fbXFlYdVRXJ7BM:

This one? https://www.amazon.com/Standard-Motor-Products-UF277-Ignition/dp/B000C81WKW

There are probably lots out there that could fill the bill.

 

My modern experience with ignition is with small model engines (62 cc at most). With full-size engines, I have left what was there, except in my '62 Pinto --> mag. Also added a blower to it -- a long time ago.

Model engines use either a Hall sensor or magnet/coil (at least w/ older 3W engines). They do not require much advance, if any. Your engine probably does, and that adds some complexity You might put your sensor at the most advance ever needed, then retard for starting. Obviously, you will need rpm or some other indicator of the amount of retard from the most advanced position. Sorry I can't be of more help. There are some real IC engine folks on this forum. I am sure they will chime in soon.

John

 

My modern experience with ignition is with small model engines (62 cc at most). With full-size engines, I have left what was there, except in my '62 Pinto --> mag. Also added a blower to it -- a long time ago.

Model engines use either a Hall sensor or magnet/coil (at least w/ older 3W engines). They do not require much advance, if any. Your engine probably does, and that adds some complexity You might put your sensor at the most advance ever needed, then retard for starting. Obviously, you will need rpm or some other indicator of the amount of retard from the most advanced position. Sorry I can't be of more help. There are some real IC engine folks on this forum. I am sure they will chime in soon.

John

On outboards--at least the old ones I mess with--the advance is mechanically linked to the throttle through an adjustable linkage and a rotating stator plate holding the points, so I'd not expect to have to mess with that at all.