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Kohler 20RZ surge/hunts at startup

Zephyr7

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I’m thinking this might be too high gain on the speed controller, but since it’s a bit of a PITA to get to that thing I thought I’d seek the wisdom of the forums first.

Here’s the deal: one of my two 20RZ gensets just showed a screwy issue for today’s exercise run: it would hunt a LOT right after startup. Then settle down, then hunt a LOT. It kept doing this for maybe 5-10 minutes and settled down when it got up to operating temperature. Voltage was pretty stable the entire time, but frequency was in the 55-65 range during the hunting. You could see the actuator on the throttle crank it open and then swing back a forth a fair bit (way more than the normal small jitter) while it was doing the hunting/surging.

I’m thinking the gain needs to come down a bit on the speed controller but it seems odd to me that it got more stable and settled down completely when it warmed up all the way. This is an NG unit and the block heater is failing so it’s starting cold (I’m guessing outdoor ambient temp so around 50* today).

Any ideas of things to check besides fiddling with the gain? I don’t see any loose connections or chewed wiring. This unit has been solid for about two years since I found the squished plugs that were causing misfires before.

Bill
 

LWB250

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I would check the regulator vent to see if it's obstructed. Governor gain settings don't change or drift significantly over time, it's most likely a fuel system related issue.

Dan
 

Zephyr7

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Regulator vent is clear. Engine sounds ok when running. I’m thinking about checking the mag pickup since I’ve seen them get weird before they fail in the past. The only thing strange to me this time is that it gets ok once it warms up which makes me think mechanical.

It has been pretty wet and rainy the past several days. Maybe just something was damp? I did check the air filter though and that was fine, and dry.

Bill
 

Zephyr7

Registered
I ran the unit again today and it did the same thing several times. I can’t find any mud dauber gunk in the regulator vent (although they did fill up some unusued bolt holes on the engine castings), and nothing seems chewed, damaged, or clogged. I popped off all the spark plug wires to see if I had any bad connections and they all look clean without carbon trails. Hmm.

I opened up the control cabinet and backed off the gain a bit, maybe one position worth on the pot so it’s maybe 1/3 from the car counterclockwise position. That seems to have stabilized things. I’m going to have to check things with my manometer when the weather is better. Today is rainy and quite windy so I just wanted to get things working quick.

The strange thing is it did stabilize when it came up to operating temperature (maybe 7-10 minutes or so), which doesn’t sound like a regulator issue. I was thinking maybe some moisture condensed somewhere due to the weather, but the early runs should have dried things out so that I wouldn’t see the issue on later runs but it made no difference.

Throttle linkage all seems to be solid.

Bill
 

I like oldstuff

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Last Subscription Date
11/09/2015
Are you sure it's not too lean? Can you fatten it up a bit to see if that helps?
*Dry fuel engines also can surge if too rich. Just mess with the mixture and see if it improves.
 

Zephyr7

Registered
Are you sure it's not too lean? Can you fatten it up a bit to see if that helps?
*Dry fuel engines also can surge if too rich. Just mess with the mixture and see if it improves.
I have to check the procedure to adjust the mixture on this unit. I think it’s the big spring loaded screw on the right of the throttle assembly but I’m not 100% sure. I tried moving that screw about 1/4 turn either direction while the unit was running poorly and it made no change. I also need to check supply side gas pressure with my manometer.

The only thing I know changed is that the block heater no longer keeps it reliably hot. The block heater seems to work when it gets really cold out (below freezing), but not at all when it’s warmer than that. It used to keep the engine around 80-100 all the time. And I can say that the unit has run reliably without the block heater since the block heater quit early this year and we’ve run on generator a few times since.

Bill
 

Zephyr7

Registered
Check the timing also.
Do you think the timing being of could make a problem that would be pretty bad cold and gone when warmed up?

The unit doesn’t even have 500 hours on it so I never thought to check the timing belt. I suppose someone before me could have messed with it though. I bought it used.

Bill
 

Birken Vogt

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These units did like to jump timing belts but I never heard of one that did and still ran at all.

What I meant was ignition timing. I have found it advanced or unstable leading to speed regulation problems more than once. Open up the distributor and see if the head of the shaft is stable inside the bushing and all that.
 

Zephyr7

Registered
What I meant was ignition timing. I have found it advanced or unstable leading to speed regulation problems more than once. Open up the distributor and see if the head of the shaft is stable inside the bushing and all that.
This is one of the newer units with the electronic ignition module. As far as I know, it has no adjustments at all. There must be a crankshaft position sensor somewhere, I could check that. I’m thinking it’s up in front somewhere hard to get at. Whomever designed the belt guard on this thing didn’t think too much about accessibility. I was really glad I had my extra long 1/4” extension bars when I replaced the thermostat. Some of the fasteners on the guard are pretty hard to reach.

Bill
 

Zephyr7

Registered
I checked gas pressure at the genset with my manometer today and it’s about where it’s always been, about 5” WC while running. Lower than I’d like, but steady and within range according the the 20RZ datasheet.

The lower gain on the speed control helps to prevent the surging and hunting, but there are still occasional speed dips that I can hear (and see) while the unit is running — it’s just more stable recovering from those now.

Something else must have changed somewhere. I’m planning to check the mag pickup, but doubt that’s the problem. I’m thinking the fuel suggesstions might be right, does anyone know the procedure for setting the mixture correctly on this unit?

Bill
 

Zephyr7

Registered
Looks like the problem might be running a bit lean. I put my manometer on the gas supply this morning and a little over 4.5” WC running. I know it has always been low, around 5ish. I was able to adjust the serving gas regulator up about 1”, so now it’s a little over 5.5” while running. I can only adjust up to a little over 6” which is still pretty low.

I have to play with the unit some more to be sure, but I’m starting to think it was not happy with the low gas pressure even though it’s always worked in the past. Perhaps the lower temps without the block heater running reliably pushed it over the edge. I’ll have to have the gas co swap out the meter and regulator and go up to 11” WC.

Hopefully I can get a new block heater on before winter sets in. Local dealer service manager is a friend of mine and recommends the 80-100 temp range.

Bill
 
Having a similar issue with mine how are you making out with yours? how do you adjust the on board fuel reg? Where you able to fatten the mixture?
 

pegasuspinto

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After several years, it's not unusual to need to set the gain.

As for the block heater, I always try to eliminate that silly external thermostat on Kohler, it's a weak point. You can buy that thermostat harness separate, if you really have to have it. Or use the following heater, which is what every other manufacturer uses.
https://www.amazon.com/HOTSTART-ENGINE-HEATER-TPS101GT8-000-PRE-HEATER/dp/B017I5HRR8/ref=sr_1_fkmr0_3?ie=UTF8&qid=1548223408&sr=8-3-fkmr0&keywords=kim+hotstart+1500w+120v
 

Zephyr7

Registered
The issue seems to be related to the engine being cold. It never showed the problem when the block heater was working reliably. I think what is happening is oil is circulating well for the lifters (it has hydraulic lifters) when it’s cold, so they don’t self adjust. This results in the valves being slightly off until the engine warms up a bit, which usually takes maybe 4-5 minutes. Once it’s up at operating temperature it runs fine.

I haven’t replaced the block heater yet so I can’t say for certain that fixes it, but I’m oretty comfident it will. A friend of mine who is the service manager at a Kohler dealer said the 80*F block heater will be fine and even a bit better than the 100*F one, so I’ll be using the lower temp unit to save a bit of money in the winter.

Bill
 

pegasuspinto

Registered
I wouldn't say better, so much as cheaper. "best" would be oil and temp kept as close to operational temp as possible.

IMHO, for home use, I would put the block heater on a switch. Turn it on when the temp maybe is unusually cold, or there are storms brewing and a power outage is likely. In really cold weather you might be spending $50-$150 a month just to keep the generator warm! You're always fighting a semi-loosing battle trying to heat an engine that's open to the cold air with the same coolant that is trickling through the radiator.
 
I wouldn't say better, so much as cheaper. "best" would be oil and temp kept as close to operational temp as possible.

IMHO, for home use, I would put the block heater on a switch. Turn it on when the temp maybe is unusually cold, or there are storms brewing and a power outage is likely. In really cold weather you might be spending $50-$150 a month just to keep the generator warm! You're always fighting a semi-loosing battle trying to heat an engine that's open to the cold air with the same coolant that is trickling through the radiator.
When your block heater is off doesn't your alarm go off?
 

pegasuspinto

Registered
There is a low temp alarm on most Kohlers, to let you know if the block heater fails. It's always on but it's not a latching alarm or a shutdown alarm. In other words, this alarm works even when the set is off, but it won't stop the unit from starting (or trying to start at least). As soon as the temp is above the threshold, the alarm quits. The alarm on older Kohlers was just another sender, and it could be disabled by removing the wire.
 
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