Small engine diagnostic help - Yamaha generator

It's not my department, but won't the PF of a transformer driving a resisitive load be close to unity, once the xformer's start-up surge has passed? My load is a space heater of wattage close to the generator's rating.

No, I thought of that, but haven't been ambitious enough yet to gather all the lamps in the house that still have tungsten lamps in one place. The "relatively small" load I spoke of that kills the generator is a large 310W soldering iron (not a gun). I understand the iron will draw more current cold than hot, but haven't checked how much more. I'm pretty confident the motor is not performing up to spec, but you're probably right in that I don't have a real good fix on just how off it is.

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Your variac is gonna be really reactive, power factor wise. The inverter may be getting confused about the phase shift between the voltage its supplying and the current demand that follows.

Have you tried it on a purely resistive load like increasing numbers of incandescent lights?

--Winston

Can you see the throttle control? By that I mean whatever opens the throttle in response to load. It's an solonoid, I suspect....

Is it slamming shut, or opening further to no avail?

No. The current peak through a purely inductively reactive load will continue to arrive 90° later than the voltage peak as long as the load is connected.

As you say below, incandescent loads draw much more current when cold than when they are hot. Your clamp-on ammeter will tell you if the relatively cold space heater is causing the inverter to current - limit.

You might have the 'Perfect Storm' test there! (Reactive load at maximum current).

If you can get a Hall effect current probe and plug it into your digital storage scope, you could get a good idea of how much power that soldering iron draws in the first few cycles. You would find that interesting and a little depressing.

I'm beginning to understand why generator demonstrations often include a load panel of dozens of incandescent lamps. The inrush of each additional lamp is not all that high and power factor ~1.0.

It can be impressive but it's almost like cheating.

--Winston

That's encouraging. It does act as though it could be starving for fuel. The high speed jet is what's called the "main jet" (#22) in this page from the parts manual, right?

I looked at it and #19 under magnification before blowing them out and they looked clear, but the orifice in that jet is mighty small. If that's the right jet, I'll try it again.

It's a tiny stepper motor.

It's hard to see working alone the way I had things set up, but I'm pretty sure the throttle is opening and the engine fails to respond. To be 100% sure I'll have to get someone to apply the load while I watch the throttle. The symptoms would be consistent with the throttle actuator responding too slowly to increasing load.

Sounds like it may be to lean to accept the load. As others have noted, see what the throttle is doing when it won't accept the load. It's probably opening up to no avail. If the jets are clean and you have good fuel flow, make sure the float level is correct if this is a float type carb., otherwise check for any air leaks that might be leaning it out. It does not take much of an air leak on an engine this small to give a lean condition. As these carbs don't usually have an accelerator pump, the carb needs to be a tiny bit net rich to accept a load increase when the governer pops the throttle open. Weak ignition can also behave somewhat like a lean condition, as a lean mixture takes more voltage to fire as does increased cylinder pressure which occurs when the load is increased. Make sure you have a healthy spark, ie it can jump at least 3/8".

Are your jets adjustable?

Wes

It's been a long time since EE 412, Transformers and Machines. But surely the transformer input should reflect the output, +/- 3dB [as the joke goes...]

Otherwise, EVERY load on the grid would appear to be fully reactive to the grid; as there's not a consumer out that who isn't fed via multiple transformers. [132KV->13.2KV; then 13.2 to 240/120, etc]

I'd sooner blame the high speed jet...

If I didn't miss something, this is a resistive soldering iron. Ohming it and doing the calcs would give worst case load.

Wes

With the obvious safety precautions, try emptying the gas tank, cleaning or replacing the filter/strainer and using fresh gasoline. It could be the fuel is flowing insufficiently from the tank and starving the pump and the floatbowl under high loads.

Dismantle the carb, run in an ultrasonic cleaner with a good solvent, blow all the ports clear and dry with compressed air, reassemble.

Can you try waving an unlit propane torch around the carb/ air intake? If it is an air leak, the torch will find it. And if it's just lean, it may help...

I learned that regardless of cleaning or appearance, a new spark plug will sometimes clear up mysterious engine troubles, including failure to accelerate or develop adequate power. Your symptoms are classic for fuel starvation, but even things like stale fuel, weak ignition, or restricted exhaust can have very similar symptoms.

Don Young

It also needs to be a tiny bit net rich to make sure that the piston crown remains in one piece. Air cooled engines and lean running, not a good combination.

Change the plug - it's a cheap problem point to eliminate.

Might need to run a video camera watching the throttle as you load it up - Paint the linkage for good contrast. It could open fully as suspected, but once the computer sees that the engine isn't responding to the throtle call and working harder after a second or two, it slams to Off and does a load dump. You would need to review the video to see it.

Rig your own variable load bank - get a Contractors Work Light string with ten lamps, and then you can screw in the lamps one at a time (with gloves on!) to vary the load.

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Ned Simmons used his keyboard to write :

If it is similiar to the Honda inverter models, on an overload condition the inverter stops outputting, but the engine keeps running. An engine restart is required for the output to resume.

Since the consensus is that the problem is in the carb, I'll do that once I've had a closer look at how the throttle actuator is behaving.