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Natural Gas to Propane conversion for genset?

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Posted by Carla Fong on January 16, 2005, 4:42 pm

Hello all -

we've acquired an Onan JS series genset that was plumbed for Natural Gas....

It has a Garretson KS regulator (Zero Governor) feeding to the carburetor

Can I use the same regulator and just supply it with propane at appropriate

Thanks in advance...


Posted by beertender on January 16, 2005, 8:12 pm

Yes you can. You probably have a "KN" regulator, not "KS". (typo?)

You can feed it low pressure propane, not to exceed 11" WC pressure.
You will need to adjust the load block a bit leaner.  This will usually be a
needle valve either in the hose from regulator to carb, or mounted directly
to the regulator or carb.


Posted by Carla Fong on January 16, 2005, 11:02 pm




Thanks - and yes, you are correct, it is a KN regulator...


Posted by Vaughn on January 17, 2005, 1:05 pm

     You seem to know a bit about these things!  I have an old Onan CCK that
runs on propane, and was shocked at the fuel consumption during Florida's recent
famous hurricane season.  It would probably cost me $0.00 or more per day to
run that thing at half load and I would be hauling those 100# tanks to the
dealer for filling two or three times a week.  I find myself thinking about the
seals etc. in that 30+ year-old regulator and wondering if that is my problem.
Is there any way to test it?  Should I replace the regulator just because of its

    Perhaps I just need to adjust my expectations and leave "well enough" alone?


Posted by beertender on January 17, 2005, 5:04 pm

Oof. That sure seems like a lot of propane.  I generally figure on 12 hours run
time for a 5kw gen per 30lb bbq tank. Varying loads, probably 1/2 load avg.
(I rarely actually use bbq tanks, mostly natural gas or 500 lb tanks)

Are you seeing flames shooting out of the muffler? Black soot in tailpipe?

But then, I have worked on the gen end of a CCK (gasoline) and noticed
that it has a monster of an engine.  And it only runs at 1800 rpm.  Maybe
that reduces its fuel efficiency?

As far as testing your current regulator, I can't offer much info without
knowing the exact type you have. Beam? Impco? specific model#?

If it's a simple demand regulator like a Garretson KN or SD, any problems
with seals or the diaphram would show up as gas smell or it wouldn't run.

First, make sure fuel supply pressure is correct going into whatever
regulator you have, and that the vent holes on the regulator are clear.

Next thing to check is the load block setting. Hold the governor/throttle
at a fixed position, and screw the adjustment in a half turn. If Rpm's go
up, the mixture is probably set too rich.

Things get more complicated if your system includes either a vacuum
lockoff or a fuel supply solenoid before the regulator.  The valve seat
might not be sealing against the orfice in the regulator properly, but
you don't notice any gas venting out the carb when the engine is
stopped because the lockoff is doing its job.

A related possibility is that the conversion was originally meant for
natural gas, and your propane pressure is high enough to lift the
valve by pressure only, instead of by engine vacuum.

Much can be learned by taking manometer readings before the
regulator, and between the regulator and the load block.  But if
you try this be carefull. A couple of times I've managed to suck
all the water out of my manometer and into the carb. (hint.. don't
touch the choke with the engine running.

Before I start rambling about all the different failures I've seen
with gaseous fuel systems, maybe you could give more info about
your fuel plumbing?

Regulator? Lockoff? Type of carb/conversion? How many hoses
connected to carb/manifold?


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