I want to find a simple way to delay ignition on any type of small engine.
My thinking about that is to intercept the signal from the wire that come out of the coil, add a delay, and let the signal go to the spark plug.
The delay must be adjustable something like let say that the engine run at 5000rpm and I need a precision of 1 degree so the delay should be :
(60sec. / 5000rpm) = .012 sec. / 360deg = .00003 sec.
That would be 33,333hz for clocking.

My knowledge finish right here.
Any idea wellcome.

 

The delay can't be by a fixed amount of time; it must be by a fixed amount of rotation of the crankshaft. Otherwise, at low RPM the timing will be advanced considerably when compared to the timing at full RPM.

Small engines usually use magnetos with points & condenser - at least the older ones do. Not sure what the latest engines are using. Since the ignition is powered by the magneto, anything electronic would also have to be powered by the magneto.

 

You are right, the delay must change according to the rpm. That should be take care by the electronic circuit. The circuit must calculate the rate of pulse from the sparkplug cable that will give the actual rpm. So the circuit must have a low delay that increase to a high delay according to the rpm.

 

We would probably need some details about the ignition circuit before making suggestions. As SgtWookie has stated, magneto ignitions cannot be delayed electronically.

 

I didn't exactly say that the delay of magneto ignition is impossible.

It would require that traditional components (points) be removed, and an alternative method of triggering (Hall-effect sensor triggered by ferrous material in the flywheel, voltage regulation/rectification/storage, controlled current through the coil, etc) be arranged. But, I don't have anything to experiment with other than my lawnmower - and I'm not willing to take it apart unless it's not working.

 

Are you aware of these two forum threads:

http://www.rcuniverse.com/forum/m_4344316/anchors_7554669/mpage_13/key_/anchor/tm.htm#7554669

http://www.rcuniverse.com/forum/m_3422690/anchors_7640198/mpage_8/key_/anchor/tm.htm#7640198

They give circuits, software, and instructions for making a sensor-based retard/advance for small engines. Several of us are working on finding suitable commercial substitutes for the homemade toroid transformer.

John