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  #1   IP: 12.213.224.36
Old November 28th, 2007, 07:19 PM
tlongman tlongman is offline
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Question Harbor Freight/Chicago Electric 5500W engine won't run continuously

Hi,
I have a problem I'm hoping someone can help me with. I bought a new Harbor Freight/Chicago Electric 5500 generator several months back. I use it for backup for utility power, as we live in a rural area in the Sierra Nevada foothills.

Anyway, this month when I went out to give it it's "monthly run" (just start it, warm it up, verify generator operation, charge starting batter -- 15/20 minutes), it only ran for about a minute before stopping. After restart, it ran, say, thirty seconds; next restart was, say 5 seconds. If I try to start it again, it'll only run a couple of seconds. If I let it sit for several hours, then the thirty-second thingie starts all over again.

I have verified that it is not getting fuel. As it's about to die, I can turn on the choke and it will continue to stumble along for a few more seconds.

I have eliminated any water in the gas (there wasn't any), cleaned out the float bowl to remove any foreign debris, verified that the valve and hose going to the carburetor will supply a good stream of fuel.

Being relatively engine-wise but not being familiar with the details of this engine, I'm stumped. Two things that I haven't checked might be causing the problem.

The first does not seem to be the problem, though, given the symptoms, and that's the low-oil pressure system. The low-oil sending unit (which I believe is mounted at about crankshaft-height on the side of the engine block) wire goes to a "segregating unit" (whatever that is, about .6" square, metal case) and then splices into a wire that connects the coil to the ignition switch. Consistent with other small gas engines, it appears that the coil is a magneto unit, with a hot lead going to the pressure switch and the ignition switch, whereby if either were grounded, then engine would no longer run.

The second thing, which I consider more likely, is a "thermo sw" (thermostatic switch?) and a carburetor fuel-bowl solenoid. I can't follow the wiring from this switch, as the connections into a diode trio (one wire from the "thermo sw") and the ignition switch aren't labeled (the other wire from the "thermo sw"). The actual solenoid on the carburetor float bowl bottom has two leads, one going to the same diode trio (not the same wire, though), and the other going to a fused battery + terminal. I suspect that the solenoid is shutting off gas in the carburetor, but without an adequate schematic, I don't see how this mechanism works. In fact, I haven't even yet found the "thermo sw", but that's from not having traced out the wiring but not seeing anything looking like what I think it might look like mounted on the engine. The schematic shows no direct connection between the "thermo sw" and the carburetor solenoid, except as it might occur by a connection inside the diode trio (not shown on schematic).

So I would appreciate any help that one might offer, including knowledge of how these two devices normally operate. One thing in particular I'd like to know is whether the carb solenoid turns the fuel ON or OFF when electricity is applied.

Thanks, Tom
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  #2   IP: 67.171.2.84
Old November 28th, 2007, 09:11 PM
suemarkp suemarkp is offline
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Usually, applying power to a carb solenoid allows fuel to flow. So just put a volt meter across it and make sure it always has 12V when the generator is switched to RUN.

Could you check the fuel flow with the solenoid energized? Usually these hold the bowl on, so you can't really see what is going on with it in place. Is the rubber piece on the end of the solenoid the correct shape and not swollen?

That is about all I can tell you for this problem...
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  #3   IP: 12.213.224.57
Old November 29th, 2007, 05:51 PM
tlongman tlongman is offline
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Question ... The continuing saga

Thanks, Mark.
That helps, some, I believe. I was able to start it and check the voltage across the solenoid with it running (during its 30 seconds or so) and, ASSUMING that I was able to get a good reading by pushing paper clips in the connectors, I did not get any voltage. Nor did I get any voltage when, after thirty seconds or so, it stopped running. I am suspicious, though, that I may have not had a good connection, so I'm going to rerun the test tomorrow. In the meantime, though, I'm trying to make more sense of the schematic such that I would know for certain how/when the fuel solenoid is activated. Right now, it's not clear to me at all how this whole circuit is supposed to operate or even what it's supposed to do.

I'm attaching a .gif file that shows a portion of the schematic obtained from the owner's manual. Since the actual wiring of the entity that I labeled the "diode trio" (my name .. their original schematic had no indication what this was) is obviously wrong in their schematic, I'm going to do some more research to see if I can pin down better what is happening in this "diode trio". It's also interesting that the ignition switch, when OFF, completes the circuit between the one leg of the fuel solenoid and the "diode trio", both on their schematic, as best as I can tell without anything being labeled, and my probing with an ohmmeter. The implication of this doesn't make sense, however, since the "diode trio" will not produce electricity without the unit running, so why on earth go to the trouble to complete a circuit to provide electricity to the fuel solenoid ... unless this is just a screwball way of turning off fuel. FYI, the ignition switch grounds the lead from the mag when in the OFF position, and that will stop the engine, so there's no need for any hokey fuel-shutoff arrangement. The low-oil switch also grounds the magneto circuit, stopping the engine. Bottom line, I just don't see what on earth the whole fuel-shutoff circuit is supposed to be doing.

There's also the issue of the "thermo sw". It doesn't seem to be involved in the fuel shutoff issue at all, but I can't figure out what it is. Perhaps you might know or have a guess. The physical switch is mounted on the operator's panel and is really a microswitch that doesn't seem to be physically operational, unless it's a circuit breaker of some sort, as it has a spring-loaded pushbutton, but doesn't seem to actually operate the switch. The label on the front of the operator panel says "OFF Push ON", which is of absolutely no help in determining what it's for or even how it operates. The "Owner's Guide" is of no help.

Any further help or pointers would really be appreciated.

Thanks, Tom
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  #4   IP: 24.36.91.63
Old November 29th, 2007, 06:09 PM
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From that drawing I don't see how the carb soleniod gets power when the ignition is on. The NC contact on the ignition switch would be open on run.
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Old November 29th, 2007, 09:17 PM
suemarkp suemarkp is offline
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You can disconnect the solenoid and put a voltmeter in its place to see when and if it is being commanded on. You can also direct wire it to 12V and listen to hear if its moving (or feel it while you connect/disconnect power). You could hard wire it on for a few minutes to see if it will run longer thus narrowing the problem to that circuit or solenoid.

I'm not sure of the purpose of these solenoids. I have one on my lawn tractor and it leaked. This allowed fuel to drip into the bowl and for some reason the float and needle didn't stop it. I replaced the float and needle and fuel still overpowered it (perhaps there is some alternate fuel path in the carb that will drip if not turned off at the solenoid). I replaced the solenoid and it no longer leaked fuel into the engine intake.
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Old November 30th, 2007, 11:04 AM
tlongman tlongman is offline
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Question I'm getting a little smarter

Hi Mark and Joed,
Well, I've learned a little more. After doing some research on the internet on "fuel shutoff solenoid", it appears that I really had a significant misunderstanding what it might be doing. The purpose of this solenoid, which is at the bottom of the fuel bowl, "plugs" the input to the main jet, thereby preventing "dieseling" after the engine is turned off. Surprise, surprise! It IS wired as I indicated in my abbreviated schematic. The coils provide current while the engine is running, but the ignition switch in the "run" position opens the circuit to the fuel shutoff solenoid, preventing the solenoid from being activated, thereby allowing fuel to flow to the main jet. When the ignition switch is turned off, the rectified current from the "dcw" (direct current winding?) is turned ON to the solenoid, thereby stopping the fuel flow and preventing "run on" or "dieseling". It's because this engine is equipped with CARB (California Air Resources Board) pollution controls; I don't know whether other engines of a similar genre have this feature or not.

So it seems that, at least electrically, this isn't the problem, as I did try running the engine with the solenoid wires disconnected and it still has the problem. It could still be that the solenoid's "plunger" is somehow getting stuck, though, and keeping the fuel shut off. After I let it sit for an hour or so, it will start and run for up to 20-30 seconds, so it could be that in that time some fuel leaks by the solenoid "plunger". Since the unit is nearly new, I wouldn't expect any swelling in any neoprene tip or anything, but obviously, this is the next thing to check.

BTW, I have figured out the "diode trio" by looking at the schematics of other small engines, primarily on generators. Honda has three different models that use similar arrangements. (In fact, it appears that one of Honda's models, the EB6500, is exactly the same generator, but with slightly different wiring -- for Automatic Voltage Control feature) I've enclosed a revised schematic that illustrates the use of these diodes. To sum it up, there is one single diode in there that rectifies the current for charging the battery; this accounts for two of the connections. In addition, there is a full-wave rectifier arrangement that rectifies current for use by the fuel-shutoff solenoid and this "thermo sw" arrangement. I still haven't figured out what the "thermo sw" thingie is. I had called Harbor Freight some couple of months ago about it, since the Owner's Manual does not discuss it at all, but they gave me a bull**** answer which was obviously wrong (it was so wrong, even to my limited knowledge of generators, that I can't even remember what they said!).

So, I'm going to check the mechanical operation of the fueld shutoff solenoid, to make sure it's not stuck "on". And I'm going to pursue the "thermo sw" to figure out what that is and if that might be involved in the problem, although I don't see how right now.

So any help or ideas that anyone has are more than welcome. Although I'm suspicious of the fuel-shutoff thingie, the problem could be very conventional, although I can't think of anything I haven't checked EXCEPT to make sure that the air hole in the gas tank cap is open.

Thanks, Tom
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  #7   IP: 24.36.91.63
Old November 30th, 2007, 03:46 PM
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I think you are on the right track with the mechanical stuck solenoid or perhaps some dirt has clogged it. Is there a fuel filter on the system anywhere? Change it if there is or at least check it.
The thermo switch is for the battery charger. It doesn't appear to have anything to do with the solenoid.
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Old November 30th, 2007, 07:21 PM
suemarkp suemarkp is offline
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It seemed counter intuitive that this solenoid works backwards than most. But because it is powered by a generator winding instead of a battery makes sense (DCW didn't click with me either until DC Winding came out). That is, the solenoid only gets engaged with the ingition switch off and the generator still turning. Once the genny stops turning (which indicates the engine has stopped rotating), there is no power to engage the solenoid so it goes back to its normal state (which allows fuel into the main jet).

Can you remove this solenoid without having a giant hole in the bottom of the float bowl? If not, can you remove its neoprene end? If not that, then remove it, make sure the main jet area is clear, reassemble it, but don't connect its wires. It shouldn't block or stick in the main jet if you install it and never allow it to be energized.
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Old December 3rd, 2007, 01:48 PM
tlongman tlongman is offline
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Default Good idea

Thanks, Mark.

I've been busy last couple of days and haven't piddled with the generator. Tomorrow, I'm going to do as you suggested and see if I can actually remove the "plunger" from the solenoid, so that it can't block the mainjet, and then try running the generator.

I'm becoming more and more convinced that the problem is with the solenoid, but I suppose we'll see, won't we?

Thanks again,
Tom
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  #10   IP: 12.213.224.38
Old December 4th, 2007, 03:54 PM
tlongman tlongman is offline
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Angry Problem isn't the fuel cutoff solenoid

Hi,

Well, after a thorough checking, the problem isn't the fuel cutoff solenoid. The solenoid is attached to the bottom of the float bowl with two screws and works through a hole in the bottom of the float bowl. The solenoid has a metal "plunger" in it, and there is apparently a spring holding the plunger in this "normal" position. With the solenoid removed, I can push the plunger in about 3/16" farther than its usual position, and I can pull it out about 5/16" farther than its usual position. Releasing the plunger causes it to return to its apparently "normal" position. It's not obvious to me why it isn't pushed all the way in the solenoid while in its static state -- perhaps just the way it's made.

Anyway, with the solenoid completely off the carburetor, I put my finger on the bottom of the carb to keep gas from running out and started the engine. I expected the engine to keep running, but it didn't. So, the fuel cutoff solenoid is not the problem -- about the only thing that's left, as far as I can see, is some dirt in the carb, but I did a thorough (I thought) cleaning job the other day when I removed the carb and float bowl, but apparently not good enough. I didn't remove the mainjet, though, and despite my attempts to blow air through it, it could be that there's a piece of dirt in it.

Just to recap: plenty of fuel flow through gasoline shutoff valve and hose to carb; as engine is "dying", I can turn choke all the way on and it will sort of "stumble on" for a few more revolutions.

Can anybody think of anything more than dirt in the carb/mainjet?

Thanks, Tom
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