Perhaps I'm just nuts. Perhaps I've got too much free time. Perhaps my inner greenie is starting to show through. Whatever the reason, I decided to convert my Z725 to run on propane.
I initially ordered a kit from motorsnorkel.com that included a vapor-only regulator and a rather poorly made adapter plate that goes between the air cleaner and the carburetor. Having previously changed my portable sawmill to run on propane, I already knew that the vapor-only regulator was going to cause problems with tank icing so the poorly made adapter sealed the fate on that kit and it went back. Next up was a kit from Nash Fuel in Kentucky that uses a high pressure liquid heated regulator that vaporizes liquid propane and regulates the flow all in one compact unit. This allowed me to utilize forklift style propane tanks that don't ice up because they provide liquid to the regulator rather than vapor. The actual process of installing the conversion probably took 8 hours including fabricating a few brackets and planning out where to mount everything. I wanted to make the whole project 100% reversible with no new holes or other permanent mods so there were a few challenges with mounting and routing. I ended up violating the "no holes" rule just once in order to add a toggle switch to the stock control panel. The switch allows changing between propane and gasoline by simply flipping the switch. I also ended up cutting into the factory wiring harness to interupt the fuel shutoff solenoid power. This signal is simply routed through the toggle switch and then either to the gasoline solenoid or the propane solenoid. Whichever solenoid gets power is the one that supplies fuel. That connection can be unplugged and re-configured back to factory function without the toggle switch easily if I decide to remove the propane system. The regulator is mounted right beside the oil filter so it was very easy to route the oil cooler lines through the regulator to provide the needed heat source to vaporize the liquid propane.
Once that was all handled, I got to fire it up and give it a test run to prove that it still runs normally on gasoline. The venturi adapter they provided was their first prototype using 3D printing. They claim to have sold many similar kits with a much more expensive aluminum adapter that's quite a bit bigger, but mine was the first thin plastic adapter. Unfortunately, the restriction added by that adapter plate was roughly equivalent to running with 2/3 choke applied. The engine would start and run normally at a dead idle, but any request for high speed would cause black smoke, stumbling, and overall unhealthy operation. Engaging the PTO immediately killed the engine.
Switching to propane, the engine started and ran normally to include high speed operation at no load, but engaging the PTO caused a bit of stumble and mowing grass had a noticeable reduction in power. After several days of e-mails with Nash Fuel over why their system wasn't performing well, I determined that there was simply too much restriction and the best way to reduce that is to open up the holes. I opened them up from 19mm to 25mm and tried again. This time, the engine roared to life and ran good on both gasoline and propane. I provided this feedback to Nash Fuel so hopefully they will incorporate this improvement in future kits.
So, the end result is that my thirsty little motor no longer drinks 4 GPH of $3/gal premium unleaded and now happily runs on $1.09/gal bulk propane. Propane has an octane of about 108 so there's no worry about fuel quality. I no longer have to take 3 or 4 plastic cans to the gas station every time I mow and refueling is a very clean process done behind my shop in about 5 minutes or I can swap tanks in about 2 minutes. If I run out of propane at the far end of the field, I just flip the switch back to gasoline and finish my pass. Stale gasoline becomes a real concern now so I'll be sure to put some stabilizer in every time I add gasoline and intentionally run out of gasoline at least once per year.
I didn't keep close records on the overall cost, but including the liquid tap for my bulk tank, several quick couplers, hoses, fittings, 2 forklift tanks, an adapter to refill BBQ bottles too, and a small pile of misc stuff, I'm probably sitting around $600 to $700 for the whole project. I suppose I'll eventually save enough money on fuel to pay for the conversion, but the convenience of refueling makes it a win regardless of payback calculations.
I initially ordered a kit from motorsnorkel.com that included a vapor-only regulator and a rather poorly made adapter plate that goes between the air cleaner and the carburetor. Having previously changed my portable sawmill to run on propane, I already knew that the vapor-only regulator was going to cause problems with tank icing so the poorly made adapter sealed the fate on that kit and it went back. Next up was a kit from Nash Fuel in Kentucky that uses a high pressure liquid heated regulator that vaporizes liquid propane and regulates the flow all in one compact unit. This allowed me to utilize forklift style propane tanks that don't ice up because they provide liquid to the regulator rather than vapor. The actual process of installing the conversion probably took 8 hours including fabricating a few brackets and planning out where to mount everything. I wanted to make the whole project 100% reversible with no new holes or other permanent mods so there were a few challenges with mounting and routing. I ended up violating the "no holes" rule just once in order to add a toggle switch to the stock control panel. The switch allows changing between propane and gasoline by simply flipping the switch. I also ended up cutting into the factory wiring harness to interupt the fuel shutoff solenoid power. This signal is simply routed through the toggle switch and then either to the gasoline solenoid or the propane solenoid. Whichever solenoid gets power is the one that supplies fuel. That connection can be unplugged and re-configured back to factory function without the toggle switch easily if I decide to remove the propane system. The regulator is mounted right beside the oil filter so it was very easy to route the oil cooler lines through the regulator to provide the needed heat source to vaporize the liquid propane.
Once that was all handled, I got to fire it up and give it a test run to prove that it still runs normally on gasoline. The venturi adapter they provided was their first prototype using 3D printing. They claim to have sold many similar kits with a much more expensive aluminum adapter that's quite a bit bigger, but mine was the first thin plastic adapter. Unfortunately, the restriction added by that adapter plate was roughly equivalent to running with 2/3 choke applied. The engine would start and run normally at a dead idle, but any request for high speed would cause black smoke, stumbling, and overall unhealthy operation. Engaging the PTO immediately killed the engine.
Switching to propane, the engine started and ran normally to include high speed operation at no load, but engaging the PTO caused a bit of stumble and mowing grass had a noticeable reduction in power. After several days of e-mails with Nash Fuel over why their system wasn't performing well, I determined that there was simply too much restriction and the best way to reduce that is to open up the holes. I opened them up from 19mm to 25mm and tried again. This time, the engine roared to life and ran good on both gasoline and propane. I provided this feedback to Nash Fuel so hopefully they will incorporate this improvement in future kits.
So, the end result is that my thirsty little motor no longer drinks 4 GPH of $3/gal premium unleaded and now happily runs on $1.09/gal bulk propane. Propane has an octane of about 108 so there's no worry about fuel quality. I no longer have to take 3 or 4 plastic cans to the gas station every time I mow and refueling is a very clean process done behind my shop in about 5 minutes or I can swap tanks in about 2 minutes. If I run out of propane at the far end of the field, I just flip the switch back to gasoline and finish my pass. Stale gasoline becomes a real concern now so I'll be sure to put some stabilizer in every time I add gasoline and intentionally run out of gasoline at least once per year.
I didn't keep close records on the overall cost, but including the liquid tap for my bulk tank, several quick couplers, hoses, fittings, 2 forklift tanks, an adapter to refill BBQ bottles too, and a small pile of misc stuff, I'm probably sitting around $600 to $700 for the whole project. I suppose I'll eventually save enough money on fuel to pay for the conversion, but the convenience of refueling makes it a win regardless of payback calculations.
