I have spent the last couple of days trying to sort out an engine problem (post 424238) and while doing so I got curious about the ignition timing and the advance and retard curves. So in the process of waiting for my new head and base gaskets to show up I grabbed a couple of timing lights, a variable speed drive pen and paper and started to see what I have.
I have read where initial timing of 15-20 degrees is considered normal and that the design of the electronics in the coil assembly will retard the timing at the upper rpm range. But what I could not find in in the archives was where some one had taken the time to map rpm verses ignition timing, and if there is any correlation to temperature having an effect on the timing curve. At the same time I thought it a good idea to check the stator output voltage verses rpm and electrical load and it's relationship to timing.
Now what I had on hand at the time (I was at home and not in the shop) was a Snap-On digital timing light, a 3/8" right angle heavy duty air drill with a variable speed air control and a TDC stop tool.
So first off was to create a timing mark that could be seen and since we are dealing with very small components, it had to be very straight with little doubt that it was lined up at exactly TDC. Once this was done it was now time to hook up the drill to a socket so as to spin the crankshaft and hook up the timing light. Now the timing light I used is 12v so I had 1 of my battery packs handy to supply power and of course you must remember to attach a ground lead from the engine to the timing light negative terminal to protect the timing light circuitry and prevent accidentally becoming one of those guys that mowed over his electric fence (if you have not heard the story, search for "electric fence upside down cow on fire") Also, make sure to remove the spark plug from the cylinder but attach it to the lead and ground the plug to a place so you can observe spark. You can use a spark tester but be sure it is for small engines and not the automotive trade or you can use a spark plug that has had the ground electrode/s removed. Also, even though you will not have the engine running under it's own power you still need lubrication so you can do oil in the cylinder and crankcase but I prefer to leave the carb on and gas on with the throttle closed. Just have a rag under the exhaust if you do this testing for a while as you will have oil dripping eventually.
So with a 14mm 1/4 drive socket on a wobble extension that is securely chucked in the drill I slowly started to spin the crank shaft at the rotor retaining nut while aiming the timing light at my marks. My timing light has a LED readout and a push button pad that allows 1 thumb operation of timing increase/decrease, tachometer/advance, reset and flash on/off. It is CDI compatible (not all lights will work with CDI ignitions and some will not work with solid core ignition wires)
Now there are two things you have to remember, first is the timing light is triggered by pulses it senses from the coil/plug wire and mine does not have a 2-4 cycle selection so since a 2 stroke fires every revolution you have to remember to take the tachometer reading it gives you and divide it by 2 (one half of the reading is the actual engine RPM) and the second is to make sure you secure the bike so it cannot move about.
Ok so bringing the engine RPM up with the drill slowly the timing light started to flash regularly at 350 RPM with the plug out. At that speed I adjusted the timing light advance setting until my marks lined up perfectly which showed my a timing to be 38 degrees BTDC. At 475 RPM, it started to advance more and at 1000 RPM my timing was at 56 degrees BTDC. I leveled out at 1300 RPM with an advance of 60 degrees BTDC. I repeated my test at least a dozen times and verified my timing marks were correct also.
Now I will tell you that at 150 rpm my timing is at 15 degrees BTDC but this was only accomplished with the spark plug installed so as to achieve a compression bump that allowed the rotor to momentarily speed up each revolution for the few degrees necessary to build a charge in the CDI while still maintaining a complete engine cycle in the 150 RPM range.
Now in my opinion, the timing advance I saw above 38 degrees was way too much. But I do know of certain engines that really love lots of timing for economy and smooth running under light load. So what I want to do is see if we can get a few of you who have proven happy running engines to perform this kind of testing and maybe we can start to build a timing curve chart.
BTW, my engine when I first started this testing had 220 PSI compressing at wide open throttle while pedaling the engine at 1000+ RPM. Adding an additional base gasket dropped it to 180 PSI and adding an additional head gasket dropped it to 145 PSI. I rechecked each compression test numerous times for repeatability. So if you do decide to do this, please get a maximum compression reading and attach it to your findings.
For now though if any of you have tried this and have something to share please do. Like I said, I think my timing advance is excessive imho but maybe it is normal.
Eventually I will work on a port timing map to go along with the same engine.
Darren
I have read where initial timing of 15-20 degrees is considered normal and that the design of the electronics in the coil assembly will retard the timing at the upper rpm range. But what I could not find in in the archives was where some one had taken the time to map rpm verses ignition timing, and if there is any correlation to temperature having an effect on the timing curve. At the same time I thought it a good idea to check the stator output voltage verses rpm and electrical load and it's relationship to timing.
Now what I had on hand at the time (I was at home and not in the shop) was a Snap-On digital timing light, a 3/8" right angle heavy duty air drill with a variable speed air control and a TDC stop tool.
So first off was to create a timing mark that could be seen and since we are dealing with very small components, it had to be very straight with little doubt that it was lined up at exactly TDC. Once this was done it was now time to hook up the drill to a socket so as to spin the crankshaft and hook up the timing light. Now the timing light I used is 12v so I had 1 of my battery packs handy to supply power and of course you must remember to attach a ground lead from the engine to the timing light negative terminal to protect the timing light circuitry and prevent accidentally becoming one of those guys that mowed over his electric fence (if you have not heard the story, search for "electric fence upside down cow on fire") Also, make sure to remove the spark plug from the cylinder but attach it to the lead and ground the plug to a place so you can observe spark. You can use a spark tester but be sure it is for small engines and not the automotive trade or you can use a spark plug that has had the ground electrode/s removed. Also, even though you will not have the engine running under it's own power you still need lubrication so you can do oil in the cylinder and crankcase but I prefer to leave the carb on and gas on with the throttle closed. Just have a rag under the exhaust if you do this testing for a while as you will have oil dripping eventually.
So with a 14mm 1/4 drive socket on a wobble extension that is securely chucked in the drill I slowly started to spin the crank shaft at the rotor retaining nut while aiming the timing light at my marks. My timing light has a LED readout and a push button pad that allows 1 thumb operation of timing increase/decrease, tachometer/advance, reset and flash on/off. It is CDI compatible (not all lights will work with CDI ignitions and some will not work with solid core ignition wires)
Now there are two things you have to remember, first is the timing light is triggered by pulses it senses from the coil/plug wire and mine does not have a 2-4 cycle selection so since a 2 stroke fires every revolution you have to remember to take the tachometer reading it gives you and divide it by 2 (one half of the reading is the actual engine RPM) and the second is to make sure you secure the bike so it cannot move about.
Ok so bringing the engine RPM up with the drill slowly the timing light started to flash regularly at 350 RPM with the plug out. At that speed I adjusted the timing light advance setting until my marks lined up perfectly which showed my a timing to be 38 degrees BTDC. At 475 RPM, it started to advance more and at 1000 RPM my timing was at 56 degrees BTDC. I leveled out at 1300 RPM with an advance of 60 degrees BTDC. I repeated my test at least a dozen times and verified my timing marks were correct also.
Now I will tell you that at 150 rpm my timing is at 15 degrees BTDC but this was only accomplished with the spark plug installed so as to achieve a compression bump that allowed the rotor to momentarily speed up each revolution for the few degrees necessary to build a charge in the CDI while still maintaining a complete engine cycle in the 150 RPM range.
Now in my opinion, the timing advance I saw above 38 degrees was way too much. But I do know of certain engines that really love lots of timing for economy and smooth running under light load. So what I want to do is see if we can get a few of you who have proven happy running engines to perform this kind of testing and maybe we can start to build a timing curve chart.
BTW, my engine when I first started this testing had 220 PSI compressing at wide open throttle while pedaling the engine at 1000+ RPM. Adding an additional base gasket dropped it to 180 PSI and adding an additional head gasket dropped it to 145 PSI. I rechecked each compression test numerous times for repeatability. So if you do decide to do this, please get a maximum compression reading and attach it to your findings.
For now though if any of you have tried this and have something to share please do. Like I said, I think my timing advance is excessive imho but maybe it is normal.
Eventually I will work on a port timing map to go along with the same engine.
Darren
