18hp B&S Lawnmower

I guess I would be a small engine user. You can see by my photo I’m going on my third year mowing carbon negitive!
I’ve learned a lot along the way. Sometimes my grass got pretty tall before I was making good gas again.
p.s.Hey Terry L. How about showing off your tractor?

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Hey Terry, great looking ride. Care to share any reactor details? No pressure its just very similar to what I want to do this summer. What’s the fuel?
Best regards, David

Thanks David, My first gasifier here is GEK style. 5 quarter inch nozzles, 3" restriction. My twist on it is that I have the producer gas preheat the hopper before it enters the filters.
I run wood chunks in it, about 1.25" square. I go through about a five gallon bucket for half hour cutting time.

Hi TerryG
Really clean looking system you have built there. As one who is actually loading your engine versus just a YouTube Woo! Woo! It Runs! I’d like to run an idea past you. I,ve only so far just been small engine running at stock factory gasoline/propane ignition timing settings. The vehicle guys here and some I’ve directly corroponded with say on woodgas loaded 1500-3000 RPM they show best power at min 30 degrees to 70 degrees advanced. The local almost anything goes lawnmower racers say limit to no mote than ~15 degrees advanced (gasoline) otherwise will kick back hand or eletric starter cranking to restart. They do this with flyweel rekeying. They do not care about the than misbalanced loss of smootth idle, vibration or the occasional broken crankshaft. All a part of racing.
I was looking over some of my small air cooled engines and I had thought it would be possible to mount a second ignition coil ahead of the factory and switch back and forth from a fixed starting/slow RPM run timing to a high RPM/loaded timing. But how to tie in the two different coils onto one spark plug ?? Back to an arced sliding mounting idea for adjustably.
Have you given any thoughts to ignition timing optimization for power on theses aircooled?

Steve Unruh


I had a good system for dealing with that very problem. Mike LaRosa has seen it in person and explained it real well in an old post, I don’t remember where. Basically I had a small distributor attached to the shaft with a flexible coupling, and could switch between the magneto and the distributor. I can’t find the pictures of when I had that set up. Mike has explained it several times and hopefully he will chime in here.


Nice setup. I recognize the long grass… But also periods of heavy testing and moving to the grassland. Bicyclists stopped to watch this lunatic mechanic in his overall, walking between the cows behind his funny kettle equiped old style English mower…
Guess you need the chains around the tires to bring over all these woodgas hp? :wink: Is the cyclone the only filter or do you have some material in the box above of the engine?

And yes, one can always stunn journalists by explaning you’re driving or mowing carbon negative. Who needs an electric car?


Ignition advance for woodgas will give you more power, but it is not a holy grail. An engine that never reaches full power on woodgas -like lawn mowers- and stay below 3,000 rpm do not need ignition advance.


If ya have an old thumper with points mounted outside the fly wheel… You can get approx 12 degrees+/- by using adjustable points.
I wanted to use the original contacts, so I “Frankenstiened” GM’s adjustment mechanism to the original Kohler points. Too much work wouldn’t do it that way again. Brian Miller offers a mounting bracket that uses GM points
A-1 Miller's - Starter Motors, Solenoids/Relays, Blower/Cooling Fans and Electrical Charging System Parts Also an electronicChrysler ignition that could be made to adjust as well.
Not sure if it’s the same Brian Miller that is a member here?
Here is a pic that shows a set of stock Kohler K301 (12hp) points mated to the GM adjustable style… Not all sure where the pic will be placed on the page :wink:
Ps Compression real makes a big difference as well, very easy to put thinner head gasket/different head.
Have fun! TerryL

Steve, I have mice that like to build a nest and eat my spark plug wires right at the coil. It’s not an easy task, but twice now I’ve had to replace the magnatron. Looking on the internet I was surprised to see that the magnatron advances the timing the faster the rpm’s. Added advance could still help. I’ve thought of a slide advance, but it works good enough not to go through the trouble. That spring after I got it running, Mike Anthony had his get-together. Upon demonstrating it to the crowd I was asked about the power de-rating on WG. My seat of the pants observation is about 75-80%. I seemed to be scoffed at for that answer. Normal mowing is done at about ¾ throttle and I do use full bore often.

DJ, It’s a pleasure to talk with you.
That photo of course is my first ride. I had a complex filtration box mounted on the carb. Gas would enter the side, go through a gallon of charcoal then on to the stock sponge and paper filter.
There has been a lot of changes since then! Cyclone is gone. The preheat tubes seem to be catching the heavy soot. I have parallel filter tubes filled with animal bedding. Then it goes to a multi layer fine screen right above the manifold. It is impossible to run gasoline, I have no carburetor now, just a butterfly on my supply tube.
There has been a lot of laughing about those tire chains. Mike LaRosa claims it’s my grate shaker! They have been on the tractor for 13yrs before the conversion.
Thanks for the tip on the ignition advance.
Here is a more recent photo. Another setback. Those flexi aluminum tubes sure are weepy. I had a perfect stoic mix in there when it blew! I would have never thought WG could be so explosive! It didn’t pop, it DETONATED! My ears rang for a bit after that! I have rain gutter down spout replacing that now. Great improvement, for now I can open my air mixture valve!

Terry, That electronic chrysler ignition could be a good option for me. If I decided to go through the trouble I think I would mount one on the front of my engine, oppisite of the flywheel, easier access. I also think there is more to gain with compression, expecially with these motors that I doubt are even 8 to 1.

Terry, How do you start up? I don’t see an on board suction device. I’m sure you don’t use the engine starter, right? Or are you the one that starts with propane? Thanks
Don M

Don, Here is a startup clip from the mentioned meet in Akron.

I need an off board compressor to power the ejector. The clip doesn’t show ignition of the producer. I use about a 1.5" strip of wax paper backing that comes off furnace duct tape. I twist it up, ignite it, and send it to the nozzles through my access port.
This spring I’m going to try propane ignition. It should be a lot faster start up. I’m doing this with my Ranger now and I’m supprised how fast it gets up to temp. Who would have thought that a blowtorch would get things hotter than some paper ashes??LOL

Hey Terry G.
I would like to use that setup on the next small engine build… A live timing monitor would be helpful. Maybe even use an O2 sensor, I’m not much for a bunch of instruments :slight_smile: but I’m thinking if ya only have 1 cylinder, ya probably wanna get all ya can from it. Being able to glance at meter… rather than turning knobs to see what happens would make things easier?
Timing did make a “seat of the pants” change in power and in starting.
I forgot to mention… points out some old Onan generators had adjustment built in… Couldn’t them in the Great White North.
Alotta thing I want to change on the Tractor, but they are gonna have to wait til the truck is running on Woodgas! :slight_smile:
Yuppers this Kohler is a low compression model that was rigged to burn kerosene and gasoline… I can expect a serious gain in power when I get around to upping the CR.
That pic of the shredded hose on you’re Tractor was an eye opener!
Sure would to see some video of the Ranger.

Hi Don,
There is a Squirrel cage fan mounted under the hood. (pic below)
Not much good for cold starting, not enough vacuum. It’s ok after the gasser has been stoked up, good for restarting after a 1 hour shut down. In an emergency I will start the engine on propane and supplement the fan with the engine to get it back up to temp. (not good)
The propane makes a good back up and convenient way to run the tractor for a short time.
First start of the day I use an Electrolux Vacuum motor blower through an ejector… It makes about 10 inches water column.
Starts fine on Woodgas then.
Link to a vid describing it.

All the best


Terry L, I am so glad I put an O2 gauge on the Ranger. I don’t feel it necessary on the mower. It is a different beast.

When that tube detonated it freaked out the wife inside the house. Also gave me a bruise on the leg. I’m lucky, the edge could have given me a nasty slice.

Oh ya, the ranger video. Got to psych myself up for that, start a youtube channel, yadda, yadda. I need to stop the excuses and do it. That video of me that Mike A took, well no one knew that was a video recorder. We thought he was just taking pics and asking questions. It really suprised me when he posted it. So glad he did though!

Hi guys
Great deal of information about small engine ignition timing possibilities you have all thrown out there.
For any non-engine folk reading this I’ll try and translate. Magneto ignition means needs no battery to produce the initial electrical energy to charge up load the ignition coil. Ignition coil charging is like setting the spring of a mouse trap. This initial generated energy is produced by you hand cranking or an electric starter cranking over the engine generally spinning a permanent magnet on the flywheel past a fixed in place laminated iron stack wound with copper wire. A magneto can also be a bolt on unit with its own internally spun magnets and wire core. These are common on industrial, aircraft and marine. No battery needed. But magneto spark energy determined by how fast you can crank it over.
Battery ignition means this initial electrical energy to load up charge the ignition coil is supplied by a a storage battery. Good cranking spark as long as the battery is charged and in good condition. Many of the original 1800’s early 1900’s small engines used old single cell dry cell batteries wired in series to do this. Spark would get weaker and weaker like a flashlight until not enough energy and you fell out of the sky or were then rowing back to shore. Not cool.
The engine itself does not care what the initial electrical source is, how it is triggered, only that the spark has enough final energy, with a long enough burn duration, AND occurs at the right time to ignite the compressed fuel/air charge in the combustion chamber.
Back to the charged Ignition coil as a set mouse trap. Ignition points or an electronic trigger at the proper time Interrupts the initial coil charging circuit. That flowing initial electrical current had created magnetic lines of power around the iron core/primary copper windings. These no longer being electrically flow supported suddenly collapse. The energy MUST go some where! Mouse trap trigger sprang Snap! Static electricity jump Snap! Only stored energy release pathway then available is through the secondary copper ignition coil windings and accross the spark plug tip gap. This should help you read TerryL’s excellent link with some understanding.

WayneK I figure then your flexishaft driven distributor was to give you the built in centrifugal low degree crank timing with speed variable advanced running timing? You then would spark plug wire change from magneto gasoline fuel spark use to woodgas battery distributor supplied spark?

I like ignition point triggering just fine. Yep just as you say TerryL narrow the gap to advance the fixed spark occurrence timing - widen the point gap to retard up to a no spark failure point. I like just fine as long as I do not ever have to again PITA every Spring be pulling flywheels to clean and reset point every year on mine and every else’s small engines.

No, TerryG I did NOT know that many of the late model electronically triggered mag/coils had built in RPM changing timing capability. Hah! Helps explain why all of my higher line engines run so much better . . . and explains their higher coil pac replacement cost. I will timing light check where I can as each is Spring firing up.

I agree DJ. No one thing is ever the Holy Grail. But 2-5% here, and then another 3-5% there starts to add up.
Higher compression ratios factory built into overhead valve small engines is another reason I recommend them over valve in block/flat heads when you are looking to acquire/buy. Flat heads types when you squeeze down the already tortuous gases flow in and out only gets worse with head shaving. OK for dense liquid gasoline droplets going in. Bulky woodgasses in addition to air we need all the flow ability we can get.

Of course use what you already have first. Soon enough you will want to improve. Newer stuff coming on the used market all of the time now. Ha! Ha! Oh how I have learned to kick my old iron love for my nice 121 pound electric starting 20 hp Kohler V-Twin!

Steve Unruh

On the timing and lower distributor, I sent Wayne this old link the other day but he must be busy.
Somehow I have managed not to blow up any of that aluminum pipe like Terry Grzyb did. It must have had an air leak at the gasifier end. I have had some seriously loud bangs but nothing has ever blown up yet … Fingers crossed, Mike

Hey Mike

I wasn’t able to open the video but thanks for pulling the link up.

If one has access to either end of the crank shaft on the small motors he can attach a small distributor, it is real easy to switch from the magneto to the distributor
I knew that you had described the set up very well before.

Chris and I have been working about 16 hours a day and we are beat.


Mike L, I am still firm that the spark came from the engine. There is no way ignition can come from my condensation soaked filters. Now that I’ve gotten rid of that flex I haven’t had any more “pops”.

thanks Steve for the “interpretation”. i have two sons who are deeply in love with mechanical stuff, but it skipped my generation of the family. i need all the help i can get to get up to speed.
my question: how does one size the burn tube for the size/type of engine that is going to use the woodgas?

i realize you all are talking about small engines here, but is there some principle that applies across the entire spectrum?