Niwatori
Unit is on propane, 10Kw, model 5502, serial 5101852, installed Oct. 2008. Surging began about 4 years after install. It was very intermittent, maybe 3 times a year, 10 -15 seconds each. The last 12 months surging became a real problem +/- 4-6 Hz. and voltage very unstable. Unit will surge with a load or with no load. With a load on it, if the load reduces like a freezer cycling off, surging will start. Applying about a 5 amp load like a small space heater set to low will stop the surging. I cannot leave it running unattended with a load, since the freq. and voltage gets so much out of specs. Manually steadying the rod on the stepper motor will also stop the surging.
Installed a new stepper motor and the surging is still there, but now at a faster rate, maybe twice the cycle rate. Now can not stop the surging. Here is a Youtube link that I found that shows the exact original surging problem, that I have. [url]https://www.youtube.com/watch?v=AozmccnafZU[/url]
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MacL
I'd check your fuel supply. Particularly any regulators, look for kinked copper pipes, etc. Fuel supply problems often look like stepper problem.

You should have 10-12" of water column pressure not running, with no more than a 1" drop when running.

I only use an analog manometer, it tells you so much more than pressure.

Hook up the manometer and when you energize the fuel valve with a jumper, it should instantly move to 11" with no bouncing. Bouncing indicates, a long pipe run, water in the gas pipe, or regulator vent pipe, undersized piping, or a bad regulator.

The regulator vent may be restricted. Some people attach a pipe to the regulator vent, but if the regulator is outdoors this is not necessary. Remove any pipe from the regulator vent if it is outdoors.

The regulator may have water sitting on the atmosphere side of the diaphragm, check for proper orientation of the regulator vent.

Is the fuel tank level very low?


Etc. Fuel supply issues.
State your problem, not your diagnosis.
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Niwatori
Thank you, MacL

I have a Generac tech coming, since I don't have the test equip. nor a gas certification, if the regulator has to be replaced.
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Peddler
There was a bulletin on these units which added a spring to the throttle rod connected around the ball studs on each end. I see from the video yours does not have the spring. This will possible solve the problem by taking out the slight amount of play in the throttle rod. Units after yours came with this spring from the factory but we had to add them to several when they first came out. If you can stop the hunting by touching one end of the throttle rod I'm sure this will fix the problem. Good Luck.

I just realized the video is not of your unit, check to see yours has a spring running parallel to the throttle rod.
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Niwatori
Although is not the unit I own, it is however identical. No spring on mine either.. Could the spring addition be for the 8Kw unit?
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Cobranut
The spring just serves to take up any play in the rod ends. It wouldn't hurt to add it to any linkage such as this.

Many years ago when I was working on small engines, Briggs used a similar method on most of their governor linkages.
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Peddler
The spring was for the 10KW only. They came without one originally but a product information bulletin came out calling for the addition of the spring to stop the hunting. I would add this upgrade before I spent much time on other fixes.
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Niwatori
I'll pickup a couple of different tension springs tomorrow and give them a try. Thanks
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Niwatori
Installed a spring and it made no difference. Too bad, that would have been an easy fix.
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Peddler
Check the valves and then get a good gauge on the gas pressure at the unit to see what it is doing while running.
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Niwatori
Following up on my surging problem. I replaced the stepped motor and it sounded like it was still varying RPM's, but at a faster cycle and not as many RPM's. Valves and propane pressures were good. I had to wait until I lost line power, to see how it performed under load. My main breaker is in a +/-40 year old panel. I dare not turn it off. Lost power for 15 hours due to storm. Voltage was 117 to 121 depending on load. Frequency was at 60 cycles, and continually fluctuated +/- .3 Hz (decimal 3hz). If decimal 3hz is an acceptable fluctuation, please let me know, then the problem is resolved. Thanks
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Peddler
Should be steadier than that, try placing your finger on the end of the throttle rod an apply the slightest pressure see if this helps, if it does then it is a linkage problem. Otherwise try playing with the fuel pressure.
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