Generator speed fluctuates at light load

[Dave Sherman]

Predator 4000, 65 hours on it. Have always run it dry before putting it away, run it once a month. Still has stock spark plug, don't know if that has something to do with it. Starts on first pull and runs great, except for on annoying quirk. If I plug in my 500 watt halogen lamp, the speed oscillates slightly. I can see the governor arm and throttle moving as it speeds up and slows down. If I plug in another 500 watt halogen, it runs steady. It also idles steady. Only at 500 watts it seems to oscillate.

I see the governor arm has a series of holes where the spring connects, could adjusting the spring to a different hole fix it?

 

[Brian123]

Does this Generator have an Oil Level Sensor on it? I unplugged mine and it ran perfect, with the Sensor on it ran like yours.

 

[wag123]

Don't mess with the governor. The engine needs to stay right at 3600 RPMs to maintain 60 hz AC output. You have a small fuel restriction in the carburetor's idle circuit causing it to run slightly lean at light loads. The governor is trying to keep it at 3600 RPMs.

 

[zeky]

Keep a 1,000 Watt load on it.

 

[Dave Sherman]

Don't mess with the governor. The engine needs to stay right at 3600 RPMs to maintain 60 hz AC output. You have a small fuel restriction in the carburetor's idle circuit causing it to run slightly lean at light loads. The governor is trying to keep it at 3600 RPMs.

Let me rephrase, would changing the spring to a different hole and readjusting the idle speed to 3600 RPM using the provided idle speed adjustment screw have any effect? I'll look at cleaning out the carb, I checked the sediment bowl at the fuel valve and it had a little bit of crud in the bottom.

Does this Generator have an Oil Level Sensor on it? I unplugged mine and it ran perfect, with the Sensor on it ran like yours.

As expected, makes no difference whatsoever. It's not like the ignition is cutting out because the level sensor is tripping. If it was, it would not run properly at any load.

 

[wag123]

Let me rephrase, would changing the spring to a different hole and readjusting the idle speed to 3600 RPM using the provided idle speed adjustment screw have any effect? I'll look at cleaning out the carb, I checked the sediment bowl at the fuel valve and it had a little bit of crud in the bottom.

All it takes is a "little bit" of crud in one of the carburetor's tiny low speed circuit passages to cause surging. As you increase the load, it uses the low speed circuit less and less, that is why it smooths out. I reiterate, leave the governor alone, it is working the way that it should be working.

 

[Dave Sherman]

Well, it turns out the carburetor was immaculately clean. The sediment bowl did what it was supposed to do. No particles, crud, varnish or gunky stuff in the carb anywhere, it was all shiny and clean inside. Cleaned out the main jet, emulsion tube, and the idle jets anyway, and it made no difference.

Moved the spring one hole out on the governor arm (increasing the spring rate), and lo and behold, it settled down with the 500 watt load. Adjusted the low idle for 62 Hz at no load, and at 3000 watts I tweaked the governor screw for 59 Hz. Rock solid at 500 watts now.

 

[Dave Sherman]

Well, it seems I wasn't quite done. Noticed that while I had it running smoothly at light loads, something was quite different when I shut the fuel valve off to run the carburetor dry. Instead of running for several seconds, starting to surge, and then surging more frequently, it sped up noticeably and ran steadily until it ran dry. Hmm... Is it running rich now? Took the carb apart again, and took a look again at the idle jet. Seems the cheap rubber o-rings that sealed it were crumbling. The lower one that was supposed to seal around the idle jet had a split in it. Ordered an assortment of o-rings, and while I was ordering, thought I might as well see about replacing the factory spark plug, presumed to be a Torch, with an NGK.

Got the o-ring replaced and the carb reinstalled, and when I got to the spark plug, got a couple surprises. First, the insulator was cracked! Now how long has it been running with a crack? Also, it was a Bosch, not a Torch. Got the NGK put in, and it started right up. Dialed in the unloaded idle, and at 500 watts it still runs steady. Now it's behaving the way it was when I shut off the fuel.

 

[Astro_Guy]

Also, it was a Bosch, not a Torch. Got the NGK put in, and it started right up. Dialed in the unloaded idle, and at 500 watts it still runs steady. Now it's behaving the way it was when I shut off the fuel.

I have a Predator 3500 Inverter generator that also came with a Bosch branded plug. The part number on the plug was Torch, not Bosch. Your plug appears to be the same. Glad to see that you had the sense to replace it with NGK. Your plug troubles are over.

 

[mk378]

That line of Bosch plugs are not good. It seems like they're rebadged Torch.

 

[Dave Sherman]

Thanks for the info. Got me curious, and I looked at the number on the plug. Manual calls out a Torch F6TC, but that "Bosch" was an F7TC. Anyone know what the effect of that would be?

 

[z71bill]

I bought an A-iPower SUA2000i INVERTER GENERATOR
1600 running watts - as a back up

I pulled the Torch plug and put in an NGK before I ever started it - Torch is trash - NGK is the best - for $2 why would anyone mess with a Torch plug?


BTW I went to RockAuto.com ordered plugs - plus extras for all 3 generators, both lawn mowers and weedeater -

Even with shipping / since I ordered so many I saved a lot VS local big box parts store - IIRC Rock Auto was $1.50 - $1.75 per plug - big box auto parts store wanted over $4 .

 

[z71bill]

Thanks for the info. Got me curious, and I looked at the number on the plug. Manual calls out a Torch F6TC, but that "Bosch" was an F7TC. Anyone know what the effect of that would be?

I have two Honda lawn mowers with the exact same engine, one came from the factory / owners manual spec is a BPR5ES the other a BPR6ES

The BPR5ES is a little hotter rating than the BPR6ES -- the hotter plug was in the newer mower and I think to improved emissions. But think you could run either plug.

I will assume the Torch F6TC runs hotter that the F7TC.