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Kohler 20RESA 20RESAL Rough Idle Fix


New member
I have some thoughts on this journey to discover the fix
but I will make that in a subsequent post about how Kohler
treats its "direct" customers.

My 20RESA would idle rough and I found a few other folks who
posted about this issue. This was real bad in WINDY days.

I looked and looked for a Service Bulletin and asked Kohler to no avail.

A friend suggested I look into the natural gas fuel vents on the regulator.

It appears to me that the intake air of the genset disturbs zero pressure
reference of the regulator at idle. Wide open (loaded or unloaded) gen ran good and did not matter because the diaphragm was full open.

The fix, 5 minutes and $5... I used two pvc 90 fittings. One on each regulator vent at the 7 & 5 o'clock postion. Screwed one end into regulator and then
slipped 1/4 inch tubing (about 2 feet in length) on each fitting.

Route tubing to an area of un-disturbed air, like against the back wall of genset, or open into PVC piping into gen set.

Take the name of the regulator off your set if you wish to research.

Anyone have more info on this or perhaps a location to locate the
service bulletins or recalls from Kohler? I asked them by phone and
email and have not had a reply.


eMail NOT Working
I don't believe this would be categorized as an engine recall situation.

What's happening here, is that the Fuel Controller (Zero Governor... Negative Regulator, etc) is simply responding to what it's seeing.

The fuel controller monitors fuel demand by comparing ambient air pressure to air pressure within the venturi of the mixer. The controller interprets this pressure differential as a change in engine load, which is compensated by additional fuel flow into the engine.

It's simply misunderstanding the situation, because the air inlet's pressure is being adversly affected by wind.

The 'bad' thing about connecting ANYTHING to a regulator vent, is that it invites the opportunity for the vent to become restricted or plugged, which can result in some Very Bad Stuff... like... total loss of fuel control... fuel leaks... and other 'bad' stuff.

What many don't realize about a fuel controller, is that it needs to be adjusted with a THOROUGH understanding of how it does what it does. The incoming fuel does NOT flow, until the control diaphram is deflected by a differential pressure above say... 4" of mercury (engine vacuum). The fuel controller is operating with an input fuel pressure of like... 11" water column... and the fuel controller needs to be set SENSITIVE enough to allow engine vacuum when CRANKING COLD... to lift the diaphram and feed fuel... yet it needs to be set stout enough to shut off fuel when the engine is NOT running. Tough balance.

Most guys solve the problem by not trying to ultra-low-idle a fuel-gas engine...

Kevin K

You may want to consider putting some sort of screening or air filter on the ends of your 1/4" tubing. Mud daubber wasps and spiders love to build nests in small openings, and you don't want these atmospheric sensing ports to become plugged.


Active member
Anyone have more info on this or perhaps a location to locate the
service bulletins or recalls from Kohler? I asked them by phone and
email and have not had a reply.
As a former employee of Kohler Power Systems responsible for service training and customer support, I can tell you that the likelihood of you receiving a response from Kohler is slim to none, unless your nit is affected by a recall.

Understand that Kohler's business model, which is similar to many manufacturers, does not have them selling or directly supporting the end users of their products. They sell directly to a distributor organization, who sells and supports the product directly to the end user. They simply don't have the resources to deal with the end users, and will direct most, if not all, inquiries to the local distributor.

So if you attempt to contact them directly, it is likely that you will get a marketing service that they employ to handle customer calls. If by chance you call the factory directly, you will be politely pointed to your local distributor.

I'm not judging or being harsh, it's just the nature of the business model.

If someone really wants to rattle cages, they can write to Herbert V. Kohler Jr. Directly, and I can assure you, there will be a response. That being said, you better be concise and detailed, and state your expectations clearly. If you go this route you may very well burn some bridges and affect the relationship with your local distributor, so I would not suggest going this route short of a last resort.

Best thing to do is to establish a good relationship with your distributor or dealer. They are the ones who are ultimately responsible for your support.



eMail NOT Working
I'll second what Kevin said...

The universal rule of fuel gas regulators, is that anyone who puts any kind of extension pipe on a regulator's vent, is giving up any benefit of every insurance policy they carry. Not only will they plug up with mud daubers, they can also load up with condensation, which freezes, hence, rendering the regulator incapable of operation.

The fuel regulation and delivery system works on the laws of physics, not the laws of man. As LWB noted, pick your battles with extreme caution- the issue you described, is not a fault of engineering, it's a fact of nature.

Ed Sparks

In Memory Of
The gas code here requires venting the regulator away from the generator. We usually use 3/4 " conduit and run it back to the tank alongside the feed line conduit. they sell a little hooded cap fitting with a screen in it that works just fine to keep the critters out.


New member
Odd that the regulator was placed in the direct flow of intake air.

I would also note that the vents on the regulator do not have screens.

Yes, I have wrapped the ends of the tubes with screen,thanks.

Thanks to all for you thoughts and special thanks to Dan for his insight, on target.

I guess I must accept that it appears I am a grey market owner of a Kohler Generator.
More on that later. Glad we have places like smokstack.


eMail NOT Working
Two things perplex me here Wayne...

First... what's the concern with how it 'idles'? I don't know the RESL, so perhaps it has some idle-down function (like my Miller Bluestar welder's auto-idle?)...

Next... you say the the demand regulator is 'in' the airflow... can you post a photo of what you mean?

The demand regulator is between the 11" W.C. side of the gas supply, and the venturi of the mixer... it's supposed to be that way, and the vent for the demand regulator isn't typically in ANY airflow area.

Is it inside some sort of a sealed enclosure? If it was intended to be in an airflow-sealed cabinet, then the demand regulator needs to be in the induction airflow path, rather than the enclosure... because the demand regulator is attempting to compare the difference between venturi pressure, and atmospheric pressure.

Was the gaseous fuel installation done at the factory, or at some other point?

Joe Batts

New member
Have your dealer / distributor adjust the advanced speed control settings in the RDC2 with Site Tech after you or them install the regulator vent tubing.

Scott Scherbon

New member
Kohler says to drill hole in base and vent regulator there. Trim carb gasket, check throttle arm bushings for excessive wear, engine speed gain adjustment (need Sitetech), have updated firmware also Sitetech needed.

While running disconnect wires to actuator, if hunting continues more then likely program problem.

Kohler Guru

New member
Your controller software needs to be updated with the newest version from Kohler. Updates are coming out fast for this controller due to problems. The update would be covered under warranty.


New member
I know that this is an old post, but I have some new relevant information and a question for any Kohler service folks.

Background is that I have a Kohler RES20A that was having starting difficulty and would regularly shut down with a Low Speed Shutdown error. Once started, it ran fine. (New plugs, Air filter, battery) After doing some research, it sounded like something related to the fuel controller and I discovered that the Kohler authorized installer squeezed the regulator vent hose out the gas pipe hole (which is about 2” above the ground) and the constricted vent hose had dirt and a leaf debris in it. I cleaned the hose and drilled a new hole for it and it seems to be running fine. I hope!

Question: In my searching, I find that Kohler now has a regulator vent hose service kit GM87489 which has 2 short hoses and 2 90 degree fittings for about $12, so of course I ordered it. Does anyone here know where these hoses are supposed to be run?

Birken Vogt

Email NOT Working
I have never used that kit but the tubes go right to the outside in the same panel where the gas and electric come in.


New member
Ok, one of my tubes goes toward the panel and then turns and goes up inside the generator housing. The other one was run outside (poorly) and now goes through a hole in the panel. 2 questions: Should I drill another hole and run them both outside? And is it a problem that these vent tubes are now outside and only 8” above ground? It seems like snow and ice could be a problem.

Birken Vogt

Email NOT Working
I don't know.

Ideally the regulator vent port would be the same place the engine gets its air, and on some larger sets they get it from after the air filter.

Inside the engine compartment for both of them or one to the engine compt and one outside sounds like a good compromise. Many only have one vent at all.

I would say just try until it works for you.
Do not route the hoses to the outside either by the gas line or through a drilled hole. Kohler went back to installing the vent tubes after starting the slow speed quiet test exercise. At full speed it is not a problem with no tubes. At slow speed the engine starts hunting badly. Like wot to closed and back repeatedly. You have two options. Don't use the quiet test exercise or install vent tubes. I route the tubes to the rear of the enclosure and terminate them in the corner behind the gas solenoid underneath the electrical connection box as Kohler does on the current models.


New member
My unit came with two hoses, one routed inside behind the electrical panel and one to the outside. The outside one appears to cause problems as I described. I like the idea of keeping both of them inside behind the electrical cover to avoid them getting debris (or snow) in them. I’m also set up to run test at full speed, but even so the fuel controller had trouble getting the engine started before the low speed error kicked in. I will run it a few days with the clean hose and new hole outside and then try inside.


Active member
Bugs love to build their nests in that tube though. That's always one of the first things to look for when working on any of these gaseous fueled gensets.