Convert Your Lawn Mower or Small Engine to Propane!

| 8/13/2010 4:17:34 PM

Tags: propane, mower, lawn mower, alternative fuels, emissions, carbon footprint, do it yourself, mechanical, Derek Sherwood,

propane mower 1My fascination with propane as a fuel for internal combustion engines began in college, with a job at a local hardware store.  We had an old Caterpillar forklift that ran on propane.  I don’t know much about that lift – it was as old as the hills – but it had begun life as a gasoline-powered model.  You could tell because they had painted over the gas gauge when they did the conversion.  I remembered noting that there were very few mechanical problems with that lift in the eight years I worked there, and also that the exhaust had a mild, throaty burble and a barbecue-grill smell when you ran it.  I was teaching myself small engine repair as a side project and I remember thinking how it might be interesting to convert a lawnmower to run on propane.

Fast-forward about twelve years.  Having successfully worked on hundreds of small engines as a side business to help pay off my student loans, as well as learned how to work on cars and other mechanical equipment, I had forgotten all about that forklift for a very long time.  One night I walked into Sears and saw something on their clearance rack in the lawn equipment section that I had never seen before – A propane-powered four-stroke weedeater.  I didn’t really have the money for it, and I had a perfectly good gasoline-powered four-stroke weedeater at home, but I talked about it enough that my fiancée went back and purchased it for me.

The Sears weedeater was made by a company called Lehr Propane, and as I researched them, I saw that they also make lawnmowers.  I didn’t have the money for a $300 brand-new propane-powered mower, but I wondered if perhaps my old idea about converting a gasoline mower to propane had gotten any more feasible.  I decided to do a little research on the internet.  I found plenty of sites talking about how it could be done; however, none of them got into detail, and none of them really seemed complete.  There was a lot of jury-rigging evident, and a lot of bad advice.  I decided to see if I could make a set of propane-powered lawnmower plans that would allow anyone to be able to do it themselves – safely and inexpensively – and make sure it was done right, the first time.

The next few blog entries will be the results of this effort.  I spent many hours reading on the internet, testing different methods shown there, tinkering and modifying the design you’ll see here to come up with an inexpensive, safe way to convert a float-bowl carburetor, gasoline-powered lawnmower to propane with simple hand tools for around $120.  The conversion takes about 1-2 hours (depending on your skill level and whether you have all of the parts available before you begin), and when you are finished you will have a lawnmower which operates exactly as your gasoline mower did before, on 1-lb cylinders of propane which are easily refillable from a 25-lb grill tank.  We’ll talk about why you would want a propane-powered mower; the benefits of propane; the precautions for working with propane; and ultimately an overview of how you can complete the project.  I hope as well that you’ll consider purchasing the plans that I have made, which comprise over 17 pages and dozens of pictures that will cover step-by-step how to do this conversion with complete material lists and vendor contact information.  I sell them on Ebay for $5 per set, or you can contact me directly,

9/19/2017 8:23:43 AM

michael_82, To the best of my knoledge on cold weather and propane, it sounds like you were using Butane, NOT Propane. Butane will stop outgassing at around freezing temps. Propane will out gass at mjuch lower temps.. Go to a Butane/Propand dealer to check me out on this.. Pa

9/19/2017 8:23:42 AM

michael_82 If you couldn't get any "Fire" at that temp. more than likely you didn't have propane, but butane. Butane will stop out gassing at around freezing temps. Check it out, common problum with butane in very cold temps...

2/9/2013 10:56:10 AM

Hi, you explained the topic very well. The contents has provided meaningful information thanks for sharing info lawn mower shops

derek sherwood
9/13/2010 10:50:33 AM

Unfortunately the Instructables guy is wrong on a few things. That was one of the pages I viewed when I went to create my plans. It resulted in me having to buy a new carburetor and start over.

kyle laser_2
9/11/2010 11:02:24 AM

This is for Dave Hammett. This should help you with converting a generator.

derek sherwood
9/9/2010 8:10:21 AM

Michael, fair enough. I have read that propane will work at 40 below, but have not tested it as such, as it rarely gets to 10 below in PA, where I am originally from. I will say that the propane forklift we used at the hardware store would perform if allowed warm-up time at very cold temps. Also, when I used to cut with a torch, we would regularly use oxy-propane cutting at 10-15 degrees below on a very cold day, and those torches pull something like a few hundred CFM at full bore. If you needed cold weather operation, a pre-heater device might be useful, or at least storing the bottles inside and then bringing them out for use.

9/8/2010 8:43:57 PM

Derek Sherwood, I have issue with your statement about the -40 degree statement. It might turn to vapor at that temp, but so slow it will not work well at any draw an engine would use. A couple of winters ago when it was only in the teens, (that would be some 55 degrees or so warmer than you stated) we had a diesel truck left out. I was too cold to start it, so we attempted to use the large propane heaters we had for the shop (full bottles of propane) set outside to blow under neath the truck. We blocked it off so the heat would stay under the hood. They would light at first when we brought them out, and they did burn for a few minutes then shortly there after died out still full of liquid, but no vapor coming out. I would not bother with any temp near freezing.

derek sherwood
9/8/2010 2:56:10 PM

You would want to wire a shut-off solenoid or other positive stop into the system so that the generator would shut off fuel when the engine stopped running. You would also want to include an automatic start. These are available from the vendors I detail in my plan set.

dave hammett_1
9/8/2010 12:12:28 PM

I've spent two days trying to get my gasoline powered generator to start. It's entirely my fault for letting it sit without a stabilizer and or starting it regularly. Is there anything different to consider with a generator?

derek sherwood
9/8/2010 10:27:25 AM

Yes, it should work on a snow blower or tractor. Propane is a vapor even down to 40 below zero, so fuel delivery would not be a problem.

tom (hubie)
9/8/2010 10:09:55 AM

Would this also work on a large snow blower? Last one I had often wouldn't start when I really needed it to. How about a lawn tractor? I could fix one up to plow with. Tom

mother earth news fair


Oct. 21-22, 2017
Topeka, KS.

More than 150 workshops, great deals from more than 200 exhibitors, off-stage demos, inspirational keynotes, and great food!