Intro: Converting a Lawn Mower or Edger From Gasoline to Run on Propane
I have a diesel VW TDI and am in the process of installing a Cummins 24 valve diesel engine in my 1964 GMC pickup so I wanted to rid myself of needing to have gasoline sitting around. The gas in my state and I am sure in most others is mixed with alcohol which attracts water and will go bad pretty quickly. This means whenever I wanted to mow my lawn, I had to either run the old gas that I put stabilizer in or go buy a gallon or so of fresh gas. I have a smoker, a coffee roaster and pressure washer that all run on propane already and have many 40lb tanks laying around so that was the logical choice.
I looked around on the interwebs and saw quite a few articles and videos of people doing this same thing but they all seemed temporary and kinda sketchy at best. I don't mind spending money if I just have to do it once and it works. This is why I used steel braided lines made for nitrous oxide systems on car engines and AN fittings for no leaks. Yes it costs more than a piece of vacuum line and a hose clamp or two but I don't have a garage or shed and the equipment basically sits out in my driveway under a carport and it will outlast me and the critters won't be able to chew through it. I chose to use the disposable 1 lb tanks commonly used for torches, grills and lanterns as you can find adapter fittings and instructions online on refilling them as this is the absolute most expensive propane available. I used -3 AN fittings and hose and that is more than adequate to run this engine, larger horse power and twin cylinder engines may require larger -4 AN size stuff
The first thing you need is a way to attach the propane tank to the system so I bought a cheap propane torch, You want one that has just a valve and no spark striker or push button that you need to hold down to keep the gas flowing. I found these on Ebay and they fit the bill. I used a tubing cutter and cut off the torch part which left me with a 1/4" OD (outer Diameter) tube with 1/8" ID (Inner Diameter). This is where it gets weird, the HVAC people use similar sized copper tubing and call it 1/8" as they use the (ID) and plumbers use the OD and call it 1/4". it is the same size as the ice maker or swamp cooler tubing commonly found at home centers in the USA. I looked and found some 1/8" copper to 1/4" NPT (national pipe thread) fittings. Then I found some 1/4" NPT to 1/8" NPT to reduce it down for the AN fitting. I should have looked for 1/8" copper to 1/8" NPT but I consider myself lucky just to find these. The copper to NPT fittings fit perfectly and I sweated them on. The torch tubing is brass so it needs more heat than copper so I used MAP gas on my torch that I used for soldering. I have since found 1/8" copper to 1/8" NPT fittings from the same supplier as the ones I used which would eliminate the 1/4" female to 1/8" male adapter fittings for a cleaner look and less expense.
Step 2: The Engine Side Plumbing
I drilled a small diameter hole in the air box on my engine through the plastic. It was just big enough for the -3AN bulk head fitting I used. this is going to differ on most every engine on how they are made, this is a Honda home gamer engine that is almost all plastic which made it easier. the fittings need 2 nuts to secure them into the plastic housing, one on the inside and one on the outside. Just use a couple of wrenches or pliers to tighten them down, you don't want any leaks that may let dirt get into the engine. They don't need any type of sealant or teflon tape.
Step 3: Holding the Tank
I did some googling and found out these propane tanks fit perfectly in 4" PVC pipe so that is what I used. I didn't want to buy a whole 20' stick of the stuff as it is very expensive and not commonly used except for commercial construction. So I found a 2' piece on Lowes.com that was shipped reasonably. I cot it off to 7" which holds the tank securely. This stuff should be able to be found on large job sites as scrap when the plumbers are cleaning up. The stuff I got is a drain pipe and not for pressure so that makes it cheaper. I also got a no pressure cap which is way cheaper than the standard cap which I glued in the bottom. I drilled a 1/4" hole through the pipe way down near the bottom and the frame of the edger and used 1 1/4" bolt to secure it, it also is wedged between the gasoline tank and a frame support which holds it secure, your mounting method will be different based on your device.
Step 4: Plumbing It All Up
I used a cheap adjustable regulator found on Ebay with 1/4" female NPT ports and installed 1/4" NPT to -3AN fittings on each end using teflon tape. I got some pre made -3AN hose assemblies from Summit Racing and they fit with flared fittings which do not need any type of sealant. The regulator I just zip tied to the control area of the edger. This regulator has no mounting holes so this may have to stay like this.
Step 5: Starting It Up
First you need to run it empty of the gasoline so it can run on propane. Once empty, turn the kill switch off if equipped and crack the throttle about half ways, propane doesn't need to be choked then just crack the adjustable regulator so you can barely hear any propane running into the carburetor then start pulling on the starter rope, you will need to find the happy place the engine likes and what I do is give it a little too much gas then back it off. You may find it easier to have someone pull the rope while you run the regulator. Once it fires and runs, you can adjust the idle with the throttle and kinda tune it with the regulator to achieve the rpm you desire.
Step 6: Refilling 1 Lb Tanks
This is the style of adapter I got to refill the propane tanks, this is not absolutely necessary if you don't mind purchasing the tanks every time they run empty but I am a cheeparoo so this is the way I roll.
Step 7: Final Thoughts
I didn't change the spark plug or even change the gap as I read somewhere you need to tighten it up a bit. I think mine is at .035 and they say to use .025 or .030. I am sure I forgot something but this is the parts I used.
Parts used: This stuff is standard type stuff, any brands that use the same size stuff will work, -3 AN is a standard size so mixing brands is fine, you don't need to use these sources, except for maybe the sweat on stuff, they were hard to find.
Propane tank: found anywhere camping or home center supplies are sold.
Torch: just one with a valve only to turn the gas on and off. Ebay http://www.ebay.com/itm/Magna-Industries-MT-200-C-...
Regulator: Ebay. any adjustable propane regulator will work, I used this one with no hoses included http://www.ebay.com/itm/Adjustable-0-to-20psi-Prop...
Copper to NPT Fittings: sweat on fitting http://coppertubingsales.com/copper-fittings/stand...
-3 AN Bulkhead fittings: https://www.summitracing.com/parts/ear-963303erl
-3 AN bulkhead nuts: https://www.summitracing.com/parts/ear-592403erl
-3 AN to 1/4" male NPT: https://www.summitracing.com/parts/ear-981643erl
-3 AN to 1/8" female NPT: https://www.summitracing.com/parts/ear-968703erl
-3 AN Hose assemblies: your lengths may vary. MAKE SURE YOU GET THE CORRECT SIZE FITTINGS: https://www.summitracing.com/search/part-type/an-h...