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20Rz Kohler LP to NG

First off I rarely post im a lurker at best. I have hit an issue I cant figure it out. I have a 20Rz Kohler. Its set up for LP. I have hooked it up to NG currently. The unit runs but not well. I'm wonder if I need to switch things to make it run properly on NG? I have searched all over with not such luck on what I need to do. I have noticed on other units when they are set up for LP the regulator is upside down and on NG its right side up. Mine is aiming down currently.

As the unit sits now its runs. It will start up bounces RPM's around a bit then steady out around 62 and fluctuate up and down .5 hertz. The electric speed controller goes back and forth like crazy to maintain the speed which it does. Small loads of 5amps at a time see to make the hertz drop deep and then recover. A load of 20 amps drop the hertz almost to 50 then it will recover bouncing around all over the place. Max load is 40amps then it starts to run out of fuel. My meter is way to small but thats a whole other issue...

I would appreciate any help..

Mac Sine

Assuming from your description of the demand regulator that your engine has an Impco carburetor. An Impco carburetor handling propane gas fuel required a negative (sub-atmospheric) fuel pressure at the carburetor inlet. Turning the "IMP" (Maxitrol) regulator upside down and removing the spring from the tower yields a nominal negative 1-inch water column outlet pressure.

An Impco carburetor handling natural gas fuel requires a nominal 5-inch positive pressure at the carburetor inlet. You will need to install a correct spring in the IMP regulator and adjust the gas pressure to nominal 5-inch positive water column. If you cannot locate a service-part spring, you may need to install a new IMP regulator. These can be purchased from Impco carburetion suppliers. Carburetion and Turbo Systems, Inc. is one supplier. (952) 445-3910.

Andrew Mackey

Last Subscription Date
As Crazydaveracing noted, if indeed that is your set up, you need to make the changes. NG has less BTUs than Propane (LPG), and thus you need more gas in order to allow the engine to operate correctly. Running as it is now on NG, it is too lean and may burn the exhaust valves if you continue to try and run it. DO NOT continue to run on NG until you richen the mixture!


I agree it sounds like it’s leaning out. There might also be a problem with your gas supply pressure. You really need somewhere in the range of 7-11 inches (for NG) at the inlet to the regulator during operation. You’ll need a manometer to check. I’ve see installations before where the pressure drops a bunch when the unit is running and then starves the unit for fuel.

You might also have your gain too high. The other thing to check is the mag pickup. I’ve seen mag pickups go bad or have loose connections that result in erratic operation of the speed control system.

It’s not hard to get the 20RZ sets running reliably. I have two that I maintain routinely and I like them a lot. They’re very reliable and easy to work on.

Thank you and everyone else for the help. The regulator is currently a maxitrol mounted up side down but it does have a spring in it? I found that odd... could it be as simple as putting it right side up? I guess I need to see what my water column is on my incoming gas as well

Mac Sine

Make sure the spring in the Maxitrol regulator is not holding the valve closed, with the unit at rest, because this would contribute to a negative outlet pressure. If this is the case, the spring will be pulling the diaphragm toward the spring tower. I have not seen a Maxitrol configured this way, but there are other, larger, gas regulators that can be configured this way.

The Impco carburetor needs natural gas at 5-inches positive water column at the carburetor inlet, so as long as you can achieve this positive pressure with the spring (a compression spring pushing the diaphragm away from the spring tower) in the Maxitrol regulator, you do not have to turn the body "tower-side-up".

Also make sure that the atmospheric vent port on the body is un-restricted.