how would someone go about making a solenoid valve whenever a cdi is supposed to spark? or just using the magneto of a 2 stroke engine? i can use a battery to power the solenoid if nessecary, im just not really sure where to even start with this, maybe a transistor connected to the cdi that controls discharge of a 12v battery to power a solenoid between an air compressor and a 2 stroke engine? and how would i retard or advance the timing via a circut? im a good with BASIC circuit and any help would be greatly appreciated maybe a drawn up circuit or an idea of how to proceed? would a cdi fry a transistor? what kind of transistor should i get?

http://www.amazon.com/Ignition-Coil-Motor-Motorized-Bicycle/dp/B00GBYJ7L2
heres the cdi
http://www.amazon.com/Magneto-Stato...8&qid=1463185322&sr=1-5&keywords=80cc+magneto
heres the magneto

 

What is the solenoid for, and what is its specification?

 

i need a solenoid valve to open and allow compressed air to enter the top of a 66 cc piston from where the spark plug was originally every time the spark plug is supposed to go off, essentially have the cdi trigger opening of the solenoid valve, which moves moves the piston, which triggers the solenoid valve which moves the piston, so on and so forth. however i need to be able to adjust the time the solenoid valve goes off in the cycle so it doesnt, "backfire", and the cdi is a POS and is not tunable. i figure it could be possible to make a circuit that is tunable somehow. i just don't know how.

 

People make two stroke engines into steam engines, doing it with air would be the same. Instead of doing it with a solenoid valve/electrically why not do it like they do it. They use a valve with a pin that hits the top of the piston at or near top dead center, the pin and valve take the place of the spark plug. One name for them is "slam valve engine", but the real name is "uni-flow". Link to one of the many out there, Google gets you many more - http://www.slamvalvemotor.com/uniflow.html

 

So you have a set of points or a contact that fires the coil at top centre, and you want to delay this electronicly, it can be done using a 555 timer or monostable chip.

 

You might want to consider using a dedicated fuel-injector control IC such as an LM1949.

 

If its a older type of engine that used a simple points and condenser based ignition system you can repurpose the points to work as your switch to trigger the solenoid fo the air.

If it has a solid state system where a reluctor or hall effect sensor that read the timing lobe for the ignition was used then that's what you would have to replicate and adapt to fire your solenoid. Or go all mechanical like others have said.

 

If it has a solid state system where a reluctor or hall effect sensor that read the timing lobe for the ignition was used

Thought that the electronic small engine (lawn mower, trimmer, etc) used the magnets on the flywheel to trigger the spark and make the power for the ignition. At least all of the ones I have do.

 

Thought that the electronic small engine (lawn mower, trimmer, etc) used the magnets on the flywheel to trigger the spark and make the power for the ignition. At least all of the ones I have do.

Yes, and what do you think is built into the ignition coil to make it create its inductive pulse at just the right time?

Look very close at your ignition coil and related systems. If it doesn't have a mechanical points and condenser setup somewhere there is a solid state pickup/driver circuit built into the coil assy someplace.

 

What was giving me a problem with your statement was the 'reluctor' comment. To my pea brain, a reluctor is used in a distributor using electronic ignition. Don't know of any small engine doing/using something like that. It is in place of the lobe's that open the points in a points ignition. And not all solid state magnetos use a hall effect anymore, they just the voltage level generated in the circuit.

 

I think you will find that the duration of any spark pulse is going to be woefully insufficient to allow enough air into the engine to enable it to run. In addition as the engine speeds up you will have all kinds of timing issues due to the response time of the solenoid. i.e. 1,000 RPM would mean a frequency of 16.67 HZ .which means your solenoid would have to open 16 times every second, allow enough air in and close again.
You will need air pressure of at least 50PSI to enable this engine to do anything, standard workshop air compressors are 140PSI so if you are going to supply your engine from one of these you will need a fairly large (and inductive !) solenoid. I doubt that something like a fuel injector , which would have the required response rate would do.You will need something much larger to allow in enough air.
Your choices are ,
1) Use some form of slam valve as previously suggested.
2) Make some form of self servo type solenoid (see how a solenoid operated common rail diesel injector works) which will give you a low inductance solenoid with a good response time. You will probably need to use some form of micro controller to control the opening and closing times based on engine RPM to ensure that you have enough air at all speeds