Points assit ignition

[Guesi]

Breakwellmz, ta, that's what I suspected.
Then I might suggest another explanation why it seemed to deliver more power: maybe your dynamo was acting as an electric motor, assisting your 350 twin? I'm not entirely certain it would do that, but it is certainly possible. Have a look at the schematic of how you switched it.

Guesi, thanks for that graph. Google tells me the Finnish title is something like 'Guesi ignition unit advance operation', and on the y-axis it's degrees, and on the x-axis engine RPM. Yes it is an advance curve, showing 0° advance below 1000RPM, then a linear increase to the factory-prescribed 22° (=3mm) advance at 2000RPM, and thereafter it stays constant. That might help if you have a problem with the engine kicking back while starting it, but: No, that is not what I am looking for.

What I'm looking for is an advance curve that gives more advance when the RPMs rise. The time it takes the crankshaft to rotate over a set number of crankshaft degrees (or mm advance ignition) reduces when the RPMs increase. The flame front, however, has a constant velocity, and consequently the ignition needs to happen earlier at higher revs. That is what none of the commercially available systems do, to my knowledge.

The pruducer of the ignition can program any advance of the ignition he wants.
But as a commercial product, you have to give guarantee for the product.
So it is the safest way to program it as near to the original data as possible.

And knowing the ideal timing in each rev. situation need a lot of testing...

[Puffs]

This also came up elsewhere. I understand & appreciate the info you gave on the ES's mechanical advancer, but there are benefits of a meaningful RPM-dependent ignition advance curve. The spark ignites the mixture, and then a flame front progresses through the combustion chamber, increasing the pressure even further. Yet the speed of the exploding mixture is more or less independent of RPM. So when the RPMs increase, with a fixed ignition timing, the progression of the flame front comes increasingly later, compared to the crankshaft position, which negatively impacts the efficiency & power output. One setting cannot be optimal for all RPMs.

Of course the speed of the flame front through the adiabatically compressed fuel/air mixture is not entirely constant, it also depends on other environmental parameters, particularly pressure and temperature. While at higher revs pressure leaking away past the piston should not be an issue, for the pressure it does matter (a lot) how far you open the throttle. With an almost closed throttle, in the idle position, the pressure in the intake manifold is low and very little mixture will pass into the engine, so that the pressure just prior to ignition will be much lower (and by consequence also the temperature of the adiabatically compressed mixture). And when the engine is hot, the mixture will also be hotter (and by consequence also the pressure of the adiabatically compressed mixture). So those 2 parameters will also influence an optimal ignition timing.

Exactly what that optimal ignition advance map would look like would need to be established by trial & error, indeed 'a lot of testing', as you say.

While browsing on the Vape site I ran into this product: http://www.vape.cz/de/technologie/ridici-jednotky/ , in English this one: http://www.vape.cz/en/technologie/ridici-jednotky/ . I needed both texts to understand it, but I think this is exactly what I meant. Unfortunately these things are quite expensive (€220 or so), and I haven't found specific information on the advance profile, or with which systems you can combine them.

Anyway, I have to correct myself: now the technology exists, there are commercially available systems that do this.

[parrbd]

Back in the seventies I had an RD400C Yamaha with points ignition. I accidently swapped the left and right carb slides when adjusting the needle position (This will keep the slides about half open) When I kicked it over it screamed its head off. I hit the kill switch. It kept screaming. I stopped it by putting it in top gear, standing on the back brake and letting the clutch out. After swapping the slides back I tried turning off the ignition whilst riding. Once I got up to a good speed I found you could ride with no spark untill you let the revs drop. This was a near new bike. It seemed that ignition timing was unimportant at high revs.

[DAVID THOMPSON]

my cousin had Yamaha 250 from the 70's
we were having problems with it fouling plugs
we put in a Bosch set from my BMW r50s
he still has the bike and he said it is still running on that 2 plugs
he put the plugs in it in 1978 and just rides it when his car is broken
and a couple times a month to keep it ride able
Dave

[Puffs]

That's quite a story parrbd!
But I have difficulty believing a normal two stroke to run without a spark, like a diesel. From an engineering perspective that makes no sense. Instead, I think something else was going on, like that kill switch making insufficient contact, so that the plugs simply happily continued to spark at their intended timing.

Yes I know there are 2T diesels, but they have a far higher compression ratio, and normally fuel injection.

Or very small, like in model airplanes. Anyway, you need to construct for it.

Dave, my ETZ is not very plug-hungry too. It can go a long time, with just a steel brush now & then.

[parrbd]

I suspect it was glow plugging at high revs in much the same way high mileage car engines will continue to run when switched off, probably due to glowing carbon deposits in the cylinder.

[Puffs]

Apologies for the derail & coming back to the topic of the thread, Andy: is the bike running fine now? With this points assist?