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paulz
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# Posted: 16 Sep 2017 22:15
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I have an old, probably Chinese generator, the ones with the copy of a Honda engine, I think it's about 4K watts. It's been a workhorse, I got it used, built my cabin with it, and it still starts first pull. Today I tried to use the same little 3 gallon pancake air compressor it used to run no problem, but the compressor started bogging down after about 30psi. I brought it home and it ran fine on grid current. The generator still runs drills and hand saws OK. Oh I also noticed the generator didn't try to rev up to increase output when the compressor started bogging down, I even reached down and revved it by hand against the governor, didn't seem to help.
So, are there some serviceable things like brushes or what have you that would help it? I measured the voltage at the plug while the compressor was running, said about 105.
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toyota_mdt_tech
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# Posted: 16 Sep 2017 23:04
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Paulz, its going to be tough to find parts. If you can get the old brushes out, you should be able to match them up and grinding on then a bit if they are bigger will work just fine too.
One issue that comes up with these lower priced offshore generators.
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paulz
Member
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# Posted: 17 Sep 2017 11:06
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Ah OK, so they do have brushes. I'll have a look, thanks!
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hamish
Member
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# Posted: 17 Sep 2017 13:35
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Brushes will have little no nothing to do with the lower voltage output of your generator. You need to measure the rpm of the motor and the hertz the generator is producing. The engine should be running at 3700rpm no load and making 60Hz @ 120V.
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ICC
Member
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# Posted: 17 Sep 2017 13:59
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Quoting: paulz Oh I also noticed the generator didn't try to rev up to increase output when the compressor started bogging down, I even reached down and revved it by hand against the governor, didn't seem to help.
So the gas engine that is driving the electric generator basically was bogging down too?? hamish is correct in that the generator output is first dependent on the proper RPM';s, which then provides the correct 120 VAC and 60 Hz. Sounds more like an engine problem to me.
Do you have a generator shop nearby?
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toyota_mdt_tech
Member
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# Posted: 17 Sep 2017 14:59 - Edited by: toyota_mdt_tech
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Quoting: hamish Brushes will have little no nothing to do with the lower voltage output of your generator.
It will if the brushes are worn out and at the end of the travel and now starting to arc. I have never worn brushes out in a generator in my life.
But it can be many things, he did mention it would load down, it most certainly can be an engine issue too or too heavy of a load
It can be too small of a extension cord going to the compressor or too long of a cord even.
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paulz
Member
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# Posted: 17 Sep 2017 15:03
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No the engine isn't bogging, just chugging along at the same rpm as with no load. Nowhere near 3700 my guess, more like half that. I could reach down and pull the rod going from the governor to the carb and rev it up, but then the governor would pull it back down. Even then didn't seem to help the output. It seems to run at one constant RPM from the moment I start it and take the choke off to whatever I pug into it. Again it runs a 1/2 drill or a Skillsaw just fine.
I may have a tack that hooks to the plug wire, how do I measure Hz?
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paulz
Member
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# Posted: 17 Sep 2017 15:04
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TMT, I did suspect the extension cord so plugged it straight into the generator plug.
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toyota_mdt_tech
Member
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# Posted: 17 Sep 2017 15:15 - Edited by: toyota_mdt_tech
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If that is a non inverter generator and a 2 pole unit, it needs to see 3600 rpm. A nice Fluke DVOM will see the 60Hz at that speed, and at 60Hz, AC voltage should be in spec range, ie 110 to 125 window. Could it be a governor issue? Does it manually throttle up? Dont try it with anything sensitive plugged into it when doing this.
With no load, running at half speed, I'd say an engine issue for sure. Not necessarily a big mechanical problem, could be a simple "control" problem, ie carb, govenor etc.
As RPM's goes up, gov will pull it down, but its strange its pulling it down with such low RPM. Throttle is pulled up with a spring, then as it reaches speeds, an internal flyweight inside the engine, driven by the crankshaft will pull it back and maintain about 3600rpm. This is a fine balance and a spring failure on the throttle could be an issue. This spring is preset and you have no manual control over it on a generator. Just check the spring that pulls throttle open. Not running, its probably going to be setting wide open, pulled by spring. Snoop in there.
Think of it as a tug of war, spring and governor, balancing at 3600 rpm, as RPM's drop, so does gov pressure, and spring pulls open throttle, as RPM'sd rise, gov pressure rises and pulls it back against the spring. This is basically the way it throttles automatically to maintain the balance.
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hamish
Member
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# Posted: 17 Sep 2017 15:26
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Quoting: paulz I may have a tack that hooks to the plug wire, how do I measure Hz?
Hz is relative to engine rpm for the most part (keeping things simple.....), 3400-3700rpm should produce 58-61hz all within range.
If you can sent a picture of your carb/governor set linkage or the model of your generator, there are lots of different set ups out there, however most are rpm regulated by an adjustable control point between the actual governor arm and the carburetor.
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paulz
Member
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# Posted: 17 Sep 2017 15:44
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OK I'l get out there next Tuesday and see what I can see, maybe take a video. Thanks guys.
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ICC
Member
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# Posted: 17 Sep 2017 17:06 - Edited by: ICC
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IIRC, a Kill-a-Watt meter reads Hz/frequency
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neckless
Member
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# Posted: 19 Sep 2017 23:39
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where the brushes contact the armature needs to be cleaned with 3 to 400 sand paper...do this to old welders...kind dangerous to do .. but best if running or a brush has no contact.. they need to move freely.... as they ware the spring has no push left....
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Steve_S
Member
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# Posted: 20 Sep 2017 06:54
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@Paul
It would be most helpful if you could provide Make, Model # and production date which should all be indicated on the machine itself. If you have an hour meter on it, let us know how many hours on it as well. If not, your best guess will still be helpful.
Depending on how accessible the bits & pieces are, have you checked all the electrical connections and linkages (may require some light disassembly) to ensure there are no loose wires or anything that has wiggled loose... the Gennies do vibrate a heck of a lot and things loosen up after a while.
Aside from feeding it gas and changing oil regularly, what other maintenance have you done to this unit... Air Filter's, lube linkages etc... not much to do BUT it all does add up.
FYI: Both my Gennies (which I depend & rely on for many things) and I have had no problems with either... Both are Chinese Made (biggy is a Champion 7200/9000, my inverter genny is a King Canada 3000w unit) I am to say the least "Anal" about that which I depend on, so maintenance is a religious thing for me... In fact after their 3rd oil change (conventional 5w30) they were switched to pure 0w40 Synthetic and that really makes a difference on small, hard working motors... I also check to make sure everything is tight, clean and functioning as intended with minor disassembly (really is minor effort) but worth it as some things (connections for electrical) have loosened and would have been problem generating.
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Kamn
Member
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# Posted: 20 Sep 2017 07:52
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I have a champion(7200/9000) and they can have the valves adjusted, carburetor cleaned, new spark plug, new air filter, and oil changed as maintenance. I went through it all when I had running issue but I ended up finding water in the fuel which caused my problem
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paulz
Member
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# Posted: 20 Sep 2017 21:19
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Today I took the cover off my crusty old generator (did I mention it's been under water, more than once). First thing I noticed, other than the filth, was the screw at the yellow arrow was gone, and the electrical gizmo it hold on was not held on by anything. The gizmo has a brass bushing in the plastic hole, maybe it's supposed to be grounded, so I took one of the cover screws and reattached it. I think the brushes are where the red arrow points, but I did not remove them. The slip rings looked fine.
Anyway it ran better today, either that screw made a difference or it got over what was bothering it the other day. I ripped long boards all morning with the Skill saw and it purred like a kitten. I did notice when you first turn on the saw the generator does bog down and coughs for a second, then resumed it usual constant RPM. I also tired the compressor again, and this time it ran until 100psi when it turns off with no issues. So for now I think I'm good. Couldn't find a tachometer, my killawatt nor a model number on the generator. Maybe it is turning 3,700 rpm, it sounds about like other generators do.
Thanks all for the replies.
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toyota_mdt_tech
Member
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# Posted: 20 Sep 2017 22:31
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well, if you threw it out today, you have gotten your moneys worth out of it years ago from the looks of it. So if its working fine now, well, puts you even further in the black. 
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darz5150
Member
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# Posted: 20 Sep 2017 22:57
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Congrats paulz on getting it going again. I have a similar one. It starts/runs fine. Doesn't need a tune up yet. But I did change the oil this year!
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toyota_mdt_tech
Member
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# Posted: 20 Sep 2017 23:23
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Quoting: Kamn I ended up finding water in the fuel which caused my problem
Stay away from alcohol fuel. To find gas free of that miserable stuff, use puregas.org or a marina or airports also alcohol free.
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toyota_mdt_tech
Member
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# Posted: 20 Sep 2017 23:24
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Quoting: darz5150 But I did change the oil this year!
LOL, funny. That thing is rough looking. 
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Steve_S
Member
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# Posted: 21 Sep 2017 07:12
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Well the old saying that a Picture is worth a 1000 words... Paul, by looking at that, it has had a Rough Life (no doubt about that eh) AND been drowned a few times too ! Hell, it still runs ! Whatever you paid for it and the use you got from it over the years I would not complain too much and certainly would NOT blame it on the "Made in China" - it still runs given it hasn't been gently treated, that has to be worth some positive points.
Now, you know what you obviously gotta do to keep it running, take it home, tear it down somewhat and clean it all up, get the dirt, filth out of the mechanisms, clean up the venting and recheck all the connections, plugs, screwed on terminals etc... You may just get a few more years of service out of it...
As for Ethanol Fuel... If you pour it in & use it up, no problem... if it sits for a week or 3 ok but not for long term storage as it can pull in water and cause issues... generally non-ethanol gas is best - even in chainsaws etc (my Husky saw only drinks Ultra-94).
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Kamn
Member
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# Posted: 21 Sep 2017 07:55
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Quoting: toyota_mdt_tech Stay away from alcohol fuel. To find gas free of that miserable stuff, use puregas.org or a marina or airports also alcohol free.
The water didn't come from the fuel itself, it somehow got in past the gas cap since there was a small pool sitting on the top of the generator from the cover keeping it there and or it could have come from the fuel can not having its cap properly tightened down when we were having heavy rainfall a while back
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NorthRick
Member
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# Posted: 21 Sep 2017 12:01
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Quoting: Kamn The water didn't come from the fuel itself, it somehow got in past the gas cap since there was a small pool sitting on the top of the generator from the cover keeping it there and or it could have come from the fuel can not having its cap properly tightened down when we were having heavy rainfall a while back
Even so, having alcohol in the fuel makes matters worse when water gets in the tank. With straight gas the water can sit at the bottom and not cause problems unless it gets sucked up. That's not true with ethanol blends. The octane of the fuel mixture can change and you'll have more issues with corrosion of fuel system parts.
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Kamn
Member
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# Posted: 21 Sep 2017 16:07
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It was true fuel
Water was separated and at the bottom of the tank
I know what ethanol fuel blends do and cause........I used to turn a wrench for a living
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hamish
Member
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# Posted: 21 Sep 2017 21:13
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Phase separation will happen with either ethanol or non ethanol fuels, just needs to sit long enough.
Any vented fuel system will absorb moisture plain and simple.
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toyota_mdt_tech
Member
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# Posted: 21 Sep 2017 22:57
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Quoting: Kamn It was true fuel Water was separated and at the bottom of the tank
True Fuel is good, spendy. I use it for my smaller stuff, ie chain saws, weedeaters, pruner pole saw. But at $100 for 5 gallons, not for my gennies. The True Fuel is race fuel. Great stuff.
If you have air space from anything other than a full tank, you can get moisture in the tank. Its in the air, separated in the tank, humidity collects on the inside of the tank...
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paulz
Member
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# Posted: 22 Sep 2017 09:01
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I've heard two schools of thought, either drain the tank and run the engine dry or leave the tank full. I do both, the stuff that mostly sits gets drained but the gennie, which may only run once a month, stays topped up.
Also heard pre-mix (two stroke) doesn't corrode tanks and carbs, dunno about that one.
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toyota_mdt_tech
Member
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# Posted: 22 Sep 2017 19:27
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Running an engine till it stalls leave the carb about half full of fuel. This will lead to corrosion, just the AL oxidation and the gunk thta collects at the bottom will create issues. You can remove the bowl and rinse it out with brake clean, then a light lube. There is an actual fogging kit, you spray it into a carb vent hose, this foams up and coats the inside and pickles it nicely.
IMHO, 12 months or more, use these. Less than 12 months, a alcohol free fuel with sta-bil will do the trick.
Otherwise, 3 options:
1) No fuel, dry inside carb
2) Carb kept full of fuel all the time (this will require turning on fuel at times as the fuel in the carb will evaporate and empty out)
3) Fogged carb
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paulz
Member
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# Posted: 22 Sep 2017 20:32
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Right, I was thinking of my chainsaw carbs that don't have float bowls. My 4 strokes (mill, pumps) have drain screws on the float bowls.
Intetesting on the fogging kit. I have some fogging oil but I think it's to keep piston rings from rusting.
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