With most of our woodgas applications I know many of us followed Wayne’s lead with a in cab timing control system but, I scrolled across a interesting idea from a YouTube channel I watch that builds micro engine RC cars and it got the thought juices flowing for a possibly simpler timing control system that would be hands off theoretically during woodgas use. Have a gander and let me know what you think?
This topic is serendipitous. After a few long runs with my gasifier powering my generator, I was wondering if I could somehow advance the timing. The mechanism to rotate the distributor is ingenious. However, I have a Honda air cooled engine with fixed timing. I am thinking of controlling the spark with a microprocessor. I would have to introduce a coil and something the equivalent of points - a solid state relay perhaps? I would love to use an Arduino but I don’t know if it has the necessary speed. Using a processor could have advantages as the degree of advancement could be adjusted on the fly.
Martin you could get a timing advance key for your flywheel, they almost always still work with gasoline, so you wouldn’t lose that option, but you would get some power back on woodgas. I have a racing gokart engine that I planned to build a motorcycle frame sort of deal for it to run on charcoal, it came with a billet flywheel that already advances the timing some but I wondered if I added an offset key if I could make this engine really hot and ready for charcoal gas.
Thanks Cody, that is a really simple and quick fix! I had no idea that those keys existed. I wonder what the downside would be on gasoline as the engine is probably set up to be optimized on that fuel.
It would just be harder to start, since newer Honda clones use solid state coils anyways it’s not like it has a dynamic advance. I would look to see how many degrees of advance it has stock, and check what your compression ratio should be. I just googled it and gx200 style engines are typically already 20-23 degrees advanced. I think the most advance key you’ll find is 8 degrees.
To go back to the main topic with a distributor, I want to say Mother Earth News adapted their vacuum advance pot to a cable control. I bet that would be pretty easy to fix to a pedal and you wouldn’t have any retarding with higher throttle.
Edit: I have been trying to find where I saw it. MEN seems to have hidden a lot of their original articles behind a paywall so I can’t exactly tell. I know they either riveted or attached a cable to the vacuum advance pot and ran that through into the cab so it would give a fixed timing advance.
the ignition system is tough environment for electronics, there are ASICs made specifically to control ignition coils. also micro controller must be protected from voltage spikes and noise.
classic arduino board with atmega328 at 16Mhz should be capable to run a single cylinder four stroke, i do use one with twin cylinder engine and it runs fine up to 2400 RPM and then start to miss the spark - it works as RPM limiter. ))
by the way, i think it is rather a code problem, not hardware limitation.
In my opinion, the optimal solution is a mechanical vacuum ignition advance regulator, on which the sensitivity of the vacuum membrane and the spring on the centrifugal regulator can be adjusted. I adjusted both on the tractor and since then there has been no need to change the ignition advance.
Perhaps I owe a slightly more “professional” explanation regarding the adjustment of the mechanical ignition regulator,…
A lot has already been said about the properties of wood gas in comparison with gasoline, but I would still like to mention them:
lower burning temperature, slower flame spread.
Given these facts, it is necessary to adjust the ignition timing. If we take operation with low revs and low load, we find that the absolute pressure in the intake manifold is higher than when operating with gasoline, so this pressure must already at a higher value move the ignition timing forward to the extreme limit with the help of the “vacuum” membrane, in practice this means that we reduce the spring force against the membrane.
Slower flame spread means that the ignition timing needs to be advanced more “aggressively” in terms of increasing the revs, which again means in practice that the springs on the centrifugal governor need to be a bit more gentle, as the engine revs don’t go as high, and the engine needs more pre-ignition even at lower revs than on gasoline, which is faster.
I don’t want to hijack this thread on distributor timing, but I thought I would just add this comment to add a final point regarding advancing timing in small engines without distributors.
The Woodruff key solution is great, but on further research I discovered the key isn’t even needed. It is only needed to fix the flywheel in its proper position for timing (duh). It isn’t needed to keep the flywheel from spinning on the shaft. The bolt does that. The video shows how to set the timing using a degree wheel.
This method would allow experimentation to find the best amount of advancement. It is still fixed across all rpm’s and doesn’t allow variation as the rpm’s increase like a distributor would, but since the generator always runs at a fixed rpm, this variation isn’t needed.
Hey Martin
On small engines, some DO need keys.
Any engine that will work be forced into a sudden STOP. Like a blade direct drive lawn mower hitting a tree root; a big rock, etc.
Small engines with an engine brake STOP band or shoes.
Small engines that hard back fire.
Even with a tapered shaft the flywheel can from rotation inertia; shift.
Electrical generators; pumps this does not happen. O.K. without a fixing key.
S.U.
Changing the timing on a single cylinder engine should be pretty easy.
Is it possible to just move the magneto head(s) on the stock ignition system? Install a new magneto bracket “earlier” in the flywheel’s travel and just mount the same magneto head there. You’d just need a little sheet metal out of the shop junk pile. Leave the old bracket in case you want to go back to “Stock”. Nothing to buy in this scenario, no need to pull a flywheel.
Generators run at a mostly fixed RPM so no need for a complex timing system that adjusts to RPM and load like a vehicle would. Keep it simple!
Anthony, newer ignition coils have a small electronic module that measures the rate of change of the magnetic field (i.e. revolutions). At low rpm it gives less pre-ignition to make the engine start more easily. At high rpm it increases the pre-ignition (typically 10–20°) to ensure combustion follows the optimum pressure. For operation on wood gas or charcoal gas, it is possible to move the coil a few degrees forward, as the mounting holes on the coil are oval and allow movement, well, you can also make these holes larger, the electronics and capacitor ignition (CDI) do the rest.
That was exactly my thought. It depends how much of a timing change you want but there is room to adjust in the regular engines and if more change is needed… you just need mounting holes in that spot! We are thinking the same here, I’ll stand down.
I have just about finished some coil brackets for my engine. I must say these are modeled upon the brackets sold for the Honda small block engines (up to the GX-200). I fashioned them because they are not available for the large block engine like my GX-340. I think this is because the smaller engines are used in the go-kart and mini-bike racing scene. Even the advance keys are designed for the small blocks.
The nice thing about these brackets is the range of timing and simplicity of changing it. No need to remove the flywheel. No messing around with a degree wheel and having to go without the key.
Please pardon the crudeness. I really needed a mill to cut the slot. 
The left plate mounts to the coil bosses using the bottom holes (they have yet to be countersunk to accept a flat head bolt). The right plate has the coil bolted to it and is fitted on top of the left plate. There are spacers welded to the right plate to lift up the coil so the brackets can lie flush on each other.
It is then a simple matter of loosening 2 screws to slide the coil and change the timing. I am going to install it in a few days to try it out.
The one bad thing is that I will have to cut the bosses to account for the thickness of the brackets. But if I need to go back to original, all I’ll have to do is assemble the coil with a few washers as spacers.
