Wednesday, March 27, 2019

A Princess Auto Power Fist 3,000 Continuous Watts Inverter Generator


[Last updated: Saturday, March 30, 2019.]

A really cheap buy. It won't start -- not so much as a burp.


Here's the User Manual.

Compression feels almost non-existent, but I'm told that that's about normal for these things. 'Next step is to see if it has spark.

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Spark Plug -- THURSDAY, MARCH 28, 2019

Removing a small cover at the machine's upper right gives access to the spark plug.


The cover is fastened by a single M6 x 12mm pan head screw, No. 3 Phillips recess.

The spark plug is way down in there. A 5/8" spark plug socket gets it out. The spark plug wire features the most peculiar looking connection boot that I've ever seen. Here's the plug out of the engine, connected for a spark test.


And I've got spark. Here's a view of the spark plug.


It's a 'TORCH A7RTC' -- 10mm thread; 5/8" hex. Gap is 0.024" to 0.028" (Call it 0.025".) It's a resistance-type spark plug. Following are the spark plug makes and numbers that are approved:
  • Bosch U24BC.
  • Champion RZ10YC.
  • Meiya (JS) A7RTC.
  • NGK CR7HS.
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Carburetor Access

At the left rear of the machine is the main service access panel.


It's fastened by a single M6 x 12mm pan head screw, No. 3 Phillips recess. Removing the panel confronts you with a rather large air cleaner.


To remove the air cleaner, proceed as follows:
  • One M5 x 20mm hex washerhead screw, 8mm A/F at the lower right. Note that there's a 10mm long sleeve associated with this screw.
  • One spring-type hose clamp at the upper left.
  • Two M6 washer-faced hex nuts, 10mm A/F up high.
And that gets us to here.


(Note that two 10mm long sleeves are likely to remain on the carburetor's mounting studs when the air cleaner is taken away.)

I could see no evidence of fuel in the carburetor's venturi, even though I'd given the starter many pulls a little earlier. Also, the spark plug appeared to be bone dry when I had it out. I clamped the carburetor in place with its hex nuts, dribbled some gasoline into the venturi and tried the starter. On the second pull, the engine caught and ran for a few cycles. So, we appear to have a carburetor that won't pass fuel to its jet. It's time to dismount the carburetor entirely, and dismantle and examine it. To dismount the carburetor, proceed as follows:
  • Two sleeves from off the studs.
  • Air cleaner to carburetor gasket.
  • Fuel delivery tube. (One spring-type hose clamp.)
  • Throttle stepper motor -- two M3 screws (No. 2 Phillips recess) with captive washers. Note that the longer one of the two screws is at the rear, where there's a brass threaded insert.
And here's a view of the carburetor off the engine.


It's a conventional float-bowl carburetor, but with a tiny stepper motor controlling its throttle butterfly. That's how the microprocessor controls engine output as required for the load that's on the inverter/generator.

Anyway, it's on to removing the float bowl to see what there is to see. I sure hope I find an evident cause for the carburetor's trouble.

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Got It Started, At Least

It appeared that the orifice between the main well and the main jet was clogged with some sort of crud. Poking a wire through it cleared that up, and after some fiddling to get fuel flowing into the carb, I got the engine to start.

It starts and gives a green "OUTPUT" LED indication briefly, then that goes out and the red "OVERLOAD" LED begins to flash. The engine then throttles down and quits. The engine can be restarted, then the same thing happens. There never is any electrical output, even when the green LED is briefly on. I'll see if I can pull off the front panel and have a look-see for any obvious fault.

Front Panel Released

Four M6 x 12mm pan head screws, No. 3 Phillips recess, fasten the front panel to the main cover set. Here we are with the front panel released.


I found and repaired two failed bullet terminal crimp connections, but neither of those was the problem. I'll completely disconnect the front panel, and get the bezel removed so I can get a good look at all the front panel's components and wiring.

- - -

And here we are with the front panel free of its bezel.


Getting to that point involved the following:
  • Disconnect all connectors. It's wise to label the connectors with a Sharpie marker, so nothing can be mis-mated at reassembly. The wiring diagram in the User Manual is quite worthless and unhelpful.
  • Disconnect one ground lead from the machine's frame. (5mm screw with captive washers, No. 2 Phillips recess.)
  • Four M4 x 8mm black truss head threading screws.
There's an encapsulated circuitry assembly that defies analysis or repair. Unit replacement is the only possible service approach.

- - -

Going Further

What the hey, I may as well tear the thing down to where I can at least get a look at the big module that's in behind the front panel. Here goes.

a) Muffler cover off. Four M6 x 12mm pan head screws, No. 3 Phillips recess.

b) Feet off. Four M6 x 16mm hex washerhead screws, 10mm A/F.

c) Two M5 x 16mm pan head screws with nuts at the underside. The screws are No. 2 Phillips recess. The nuts are 8mm A/F and are captive in recesses.

d) Two M6 x 20mm pan head screws, No. 3 Phillips recess at the front and rear of the handle.

e) One M4+ x 12mm pan head threading screw at the upper front. You have to peel back the fuel filler neck's surround in order to see it.

The right side cover is free to come away.

f) Big electronics module. Two M6 x 12mm hex washerhead screws.

And here we are.


I'll disconnect, inspect and reconnect some connectors that are now accessible. Like the small circuitry package on the front panel, the big module is encapsulated and quite unserviceable.

- - -

I found nothing amiss. I buttoned the machine back up with considerable difficulty -- it's not a pleasant chore to get the covers back on with the fuel tank correctly situated. The engine starts easily and idles nicely. There's been a slight change in my symptom. The machine now keeps running with both the green "OUTPUT" LED and the red "OVERLOAD" LED on constantly, with still no electrical output. Whatever the trouble actually is, it's beyond me to solve it.

Princess Auto has a pretty decent return policy on gear like this. We should be able to get store credit for well over what was paid for the unit, so it's not a dead loss. Anyway, I now know a little more about inverter generators than I did before I started on this.

- - -

Another Symptom -- SATURDAY, MARCH 30, 2019

By the way, I returned to the machine briefly and discovered another symptom -- the engine won't idle off choke. It just dies when the choke is opened. On the face of it, that would be a clogged idle jet, the tiny jet that's right by the throttle butterfly. I removed and dismantled the carburetor again and inspected the idle jet as best I could. The jet appears to be clear. There's a welch plug covering the idle fuel chamber. If I had a replacement welch plug I could open up and examine that chamber. That would be the final thing that I could do to try to fix the off-choke idle problem, but that's not on. So there's an unsatisfying end to the project. It's off to Princess Auto with it.

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