If your end result is to get more power/performance from the motor advancing ignition is not the only or even best way. Unless you can retard the ignition to the original setting you will - 1. make it harder to start, 2. make it run hotter. Time to go old school for more power. Most exhaust ports are round, using a square file changing the "O" port shape to an upside down "D" shape while keeping the flat part of the "D" at the same level of the original port is one way to get the motor to breath better and make more power with little more than some easy work. Another way is to take the baffles out of the air cleaner/intake box if it has them.

 

Another way is to take the baffles out of the air cleaner/intake box if it has them.

This will get more air in, but it may also weaken the mixture, increase the combustion temperature and ultimately damage the engine. Unless you also adjust the fuel/air at the carburettor this is not advisable.

 

Well guys, I'm not doing this research to try and gain more power. So any ideas to flexibly (as in research) advance the spark will be most thankfully received.

 

This will get more air in, but it may also weaken the mixture, increase the combustion temperature and ultimately damage the engine. Unless you also adjust the fuel/air at the carburettor this is not advisable.

Not really. Carburetors work on pressure differentials, more air flow pulls more fuel through the carb. It has been done like this forever in hot rodding. If it didn't work why do they make things like all of the high performance air cleaners? In my younger days I helped work on 2cycle engines with a guy that raced gokarts, then dirt bikes. In the stock engine classes this was a way of getting more HP.

 

Well guys, I'm not doing this research to try and gain more power. So any ideas to flexibly (as in research) advance the spark will be most thankfully received.

Then what are you doing it for?

 

Carburetors work on pressure differentials, more air flow pulls more fuel through the carb.

Then how do chokes work that use a butterfly between the carburettor and the air intake?

 

If your end result is to get more power/performance from the motor advancing ignition is not the only or even best way. Unless you can retard the ignition to the original setting you will - 1. make it harder to start, 2. make it run hotter. Time to go old school for more power. Most exhaust ports are round, using a square file changing the "O" port shape to an upside down "D" shape while keeping the flat part of the "D" at the same level of the original port is one way to get the motor to breath better and make more power with little more than some easy work. Another way is to take the baffles out of the air cleaner/intake box if it has them.

Probably worth a recap on why advance is needed in the first place.

Primarily its because the flame front takes a finite time to spread - you need complete combustion just the tiniest smidge after TDC, to do that you have to start the ball rolling BTDC. The faster the piston is going - the sooner BTDC you have to light it.

There is also the matter of compression - in free air; the petrol/air mixture just goes "whoomph" - lighting it at or just before maximum compression has a sort of regenerative effect.

 

Then how do chokes work that use a butterfly between the carburettor and the air intake?

The choke butterfly is between the air cleaner and the carb inlet, not in the intake port. Choking creates a higher vacuum signal, causing more fuel to come out of the discharge jets in the carbs throat. When the choke is off the air pressure differential is controlled by the throttle butterfly, this throttle opening also exposes different fuel ports to the air flow. From the idle port at closed throttle, to the transition ports at above idle and finally the one in the venturi at full throttle.
And regarding the first question 2cycle carbs usually have adjustable jets, using a needle valve to set the amount of fuel available. And they usually have a high and low speed needle valve. Setting those to match the fuel to air ratio as needed.

 

The choke butterfly is between the air cleaner and the carb inlet, not in the intake port.

That's what I said.

Choking creates a higher vacuum signal, causing more fuel to come out of the discharge jets in the carbs throat.

So changing the air resistance of the air filter would have the same effect as operating the choke which is also what I said.

 

So changing the air resistance of the air filter would have the same effect as operating the choke which is also what I said.

No. The choke butterfly is between the fuel bowl vent and the main/idle jets so when its closed the fuel bowl still has normal atmospheric pressure (or whatever the pressure is behind the air filter) while the main and idle jets are on the engine side of the butterfly being subjected to a much lower ambient (higher vacuum) pressure than the fuel bowl is at.

The only way the air filter can affect fuel flow is if it is so clogged that it creates a high enough vacuum in the whole carburetor to either be able suck the fuel out of the fuel bowl through the main and idle jets and the fuel bowl vent or cause it to flash boil at ambient temperature and be sucked up by the engine though the related jets and vent passages which I have always known that to be called hard choking.

 

This conversation has gone totally out of control. Why does it matter why I want to advance the spark??

It's not the questions I asked in the first place. I asked you guys for help on HOW to advance or adjust the timing.

Please limit your replies to the ORIGINAL QUESTION. All the other stuff is just spurious noise.

I still have not got any realistic electronic solutions After all this time Aaaah well, we live in hope

With many thanks.

 

Is your cdi simpler than this with no timing pulse?

 

This CDI image above, is way more sophisticated than the Chinese bicycle motor version. Believe it the Chinese bicycle motor version only has TWO wires going into it. After many hours of trying to understand this device I believe the approximately 100 volts a/c from the direct drive magneto is used both to power the CDI (and the internal capacitor) and trigger the discharge (when the signal goes 'high' on each cycle). One wire is definitely earthed and the other wire comes from the 'other' end of the coil in the stator.

 

This conversation has gone totally out of control. Why does it matter why I want to advance the spark??

It's not the questions I asked in the first place. I asked you guys for help on HOW to advance or adjust the timing.

Please limit your replies to the ORIGINAL QUESTION. All the other stuff is just spurious noise.

I still have not got any realistic electronic solutions After all this time Aaaah well, we live in hope

With many thanks.

Ah! and therein lies the problem with reengineering something. A good engineer can not and will not ignore other factors in a redesign or change of one component in a system.
Everything in a system has its place and function and if one function is changed the others related to it have to be refactored as well.

So far what we know is you don't plan to get any more power or efficiency from the engine which for the most part pretty much make the whole change pointless to us.

Now as for what has been covered the biggest problem is you can not change over to a electronic ignition advance control system without adding a considerable amount of extra control to do it. Especially so for a single cylinder engine that inherently has a very basic ignition design to begin with.

To do accurate and reliable ignition control on a per degree of rotation resolution over a wide RPM band requires precise crankshaft position and motion referencing and a good deal of highly accurate most likely digital control which is why no one has came forth with a schematic of any kind. It's just not a simple 555 timer IC and a pair of comparators type circuit.

 

Thank you.My best theory so far is to use a coupling 1:1 transformer which I believe should shift the timing by 180 degrees. And most probably one could include some sort of simple inductive tuning system that would vary the phase over a range. Any comments or suggestions?

 

Is this the ignition coil you are refering to as on an 80cc bike engine? Its very unusual for a CDI ignition system to only have 2 wires. Does the plastic coil assembly have a Grounding point? Also some detailed pictures of the actual coil assembly under the flywheel would be of some help. I am quite familiar with CDI ignitions on small engines, & this one doesn't add up. It may not be CDI ignition but a transistor switched Magneto..

 

And most probably one could include some sort of simple inductive tuning system that would vary the phase over a range. Any comments or suggestions?

I doubt it can be done that easily being the actual phase angle variation will change depending on the combination of the frequency input voltage and current loads across it.

Simply put it will not give you the resolution or stability you need to fire your spark plug accurately.

You can ask the question 50 times and in 50 different ways but you won't get any different answer other than it's a complicated process to handle with electronics but a very easy one to do mechanically in several different ways.

 

Yes, it's the one in your photo. Can you tell me how this works? It definitely has only two wires blue and black as per your photo. The body is completely non-conductive plastic or some such material.

 

It may not be CDI ignition but a transistor switched Magneto..

That would be my guess as well.

It's about as simple as they can get and still be a solid state system.

 

We are realy guessing as to what you have, until you provide more info such as pictures of whats driving this on the engine. This is what a solidstate ignition looks like being driven from windings under the coil.