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Kohler 2.5R21- A few general questions


Good afternoon everyone,

My Kohler 2.5R21 electric plant is currently equipped with a Carter model N carburetor for use with plain gasoline. However, on the bottom of the bowl, there is a small 'button' with a rubber washer on it. It is held in place by the main bowl screw via a flat strip of metal which provides some force to hold the rubber bit against the hole which the button pokes through. Does anyone have an idea as to what its function is? I have not seen it on any other model N carbs.

On a different note, I mentioned in the first thread I created about this generator that I had an interest in adapting it to run on propane. I did take a look at the kits offered by US Carburetion and started to wonder if a $230 dollar kit for a $75 dollar generator would really be worth it...
So I was wondering, would the propane 'venturi' from a k181-based generator work with my k161-based one, provided I use a proper regulator and load block? My reasons are as follows:
  • I realize that I'll have to remove the existing carburetor and lose the ability to run the engine on gasoline, but this isn't an issue for me.
  • I intend to use this generator for backup with its remote start functionality, but I'm not sure what to do for a stationary gas tank, not to mention the issues with storing gasoline for extended periods of time.
  • It appears as though the k181 and my k161 have the same intake flange, so the venturi should fit.
  • Finding an original gaseous fuel adapter with the oil bath air cleaner seems very unlikely.
So what do you guys think?


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I think you just need an add-on venturi with a load-valve, some hose, a demand regulator and a pair of pressure regulators... but y'know, if the kit is $230, and it's all complete, it'd be a worthwhile investment. Here's why...

If you kill the generator, the fuel system will STILL be very useful on another engine, it'll be just fine up to a K341 with no issues. It'd even fuel one of the L600/L654 four cylinder liquid-cooled 1800rpm units, or a Hercules ZXB, or similar...


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Oh, and yes, the K181 will be close enough to work with the K161 application, as long as the mechanical fitment is same.

On a gaseous fuel application, the metering is all done by the 'demand regulator'... aka 'zero governor'... aka 'fuel controller', and the mixture is all pre-set and basically error-free by virtue of very simple physics. The concept is VERY simple:

Gaseous fuel comes to the valve at some pressure... for say... a Garretson KN, that incoming pressure is 11" water column... which is same as what you'd get from the 2nd stage regulator coming into a farmhouse like mine. There's a first-stage gaseous regulator (usually red color) on the tank, which has tank pressure (from almost zero, up to about 220psi or so, depending on ambient temp), and limits it to either 10psi (most frequent) , or 2psi (not as frequent). From there, gaseous fuel travels anywhere from a dozen feet or so, up to several hundred, usually underground in either plastic or copper pipe around 1/4" to 3/8" ID or so) to a second stage regulator (often brown color) where that pressure level is reduced to 11" w.c.

The demand regulator has 11" w.c. pressure at it's inlet, and it allows flow at a regulated output.

The Demand Regulator works just like an air regulator on your compressor, with just one basic difference. follow along here:
- Let's say your shop air compressor is set to 130psi.... but your automobile air hose regulator is set to 25psi. the incoming pressure to that regulator is pushing against a diaphram that's holding a valve OPEN... but the output air from that valve flows around and acts on the OTHER side of the diaphram. There's an adjustable control spring working in the OPEN position. That incoming pressure will flow air to the outlet side UNTIL such time as the airflow around starts pushing on the diaphram. as the outlet side pressure rises, it pushes against the diaphram's SPRING, and when it overcomes it, the airflow stops. The pressure that the spring exerts on the diaphram, in conjuction with the surface area applying open vs. closed pressure, identifies what REGULATING pressure the valve will charge to.

As you lower the spring pressure, outlet cutoff pressure falls. Lower it to 15psi... then 7psi... eventually, you get down to the point where the spring is totally released, and the valve will flow NO air, even at atmospheric pressure...

...but what if you apply a slight vacuum? That draws the diaphram in the same direction the spring WOULD have, thus, opening the valve, and allowing air to flow.

Now imagine that the inlet pressure was 11" of water column... and the vacuum was being applied by virtue of a venturi in an ordinary carbeurator. The venturi is always where a gasoline main jet would be located, and for good reason- The carbeurator's main jet is purposely IN the venturi, so that the difference in pressure between atmosphere and that venturi yields enough vacuum to pull FUEL from the bowl, OUT THE MAIN JET... and while you may say the mixture is dependant upon the bore of the main jet, that dimension only matters when the engine is drawing the max amount of fuel. The REAL mixture is done by altering the fuel float level... because this changes the amount of pressure differential required to lift fuel from bowl to venturi to be evaporated and mixed with air to burn.

The negative pressure regulator valve does exactly the same thing that a float bowl does... just does it as a mechanical operation, rather than gravity-based (float valve) .

It is not unusual for individuals to open up a gasoline carb, remove the float bowl and main jet, install a fitting in the bottom of the main jet tube (a 'spud', and connect a fuel controller of some sort to make a functioning gaseous system. Some carbs (particularly high-quality carbs, frequently older machines) come with carbeurators that have both gasoline functionality, AND a spud connection dedicated to gaseous fueling.