Yamaha ef6300isde generator - 30 amp mode - flips to overload after about 5 to 10 seconds. Generator runs well and all other plugs work when switched to 120/240. Any ideas?

If you are referring to the crankcase ventilation, it could be that either the engine is overfilled with oil, or the cylinder could be glazed and the engine requires a moderate to heavy load every so often to prevent this from occurring.

I would recommend that you stick with mineral oil with a grade of 10w/ 30, even better just use the OEM stuff, or Honda 10w/30 is easily available.

Some of these small engines have a chrome bore and do not like synthetic oils, it will cause cylinder glazing and excessive blow by.

Change the oil when it is starting to become contaminated, ie. getting carbon in it, rather than guessing at hours of operation.

If it's not the CCV your referring to, it must be leaking oil from the engine somewhere and blowing back via the cooling fan, this will require a thorough clean and further investigation to diagnose correctly.

Most common areas of oil leaks are the crankshaft seals and valve cover gasket.

I personally would start with an oil change to mineral, and place generator on a loaded circuit for a while, don't kill it just load it, and see if you have any improvements.

Hope you find this helpful.

one side is hot 120v other side is neutral

No idea but somebody else will probably come along with a better idea then mine, seems a lot of these generators have this thing installed on them (Has $25 hard start kit). Not sure what it does or how it works. Strangely enough you said you use it for 240 volt. Looked at the picture and didn't see a 240 volt connection.
If you are using the what look like the 120 volt circuits you can't over load the unit. Maximum current draw will cause it to go into protection mode and shut down the power load. The following is an exert from the owners manual which I got from Yamaha's site. Link at the end of this post.

Hope this helps


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16
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q
760-029
AE00788
Overload indicator light
The overload indicator light
1
comes on when an over-
load of a connected electrical device is detected, the
inverter control unit overheats, or the AC output voltage
rises. The electronic breaker will then activate, stopping
power generation in order to protect the generator and
any connected electric devices. The AC pilot light
(green) will go off and the overload indicator light (red)
will stay on, but the engine will not stop running.
When the overload indicator light comes on and power
generation stops, proceed as follows:
1. Turn off any connected electric devices and stop
the engine.
2. Reduce the total wattage of connected electric
devices within the application range.
3. Check for blockages in the cooling air inlet and
around the control unit. If any blockages are found,
remove.
4. After checking, restart the engine.
http://www.yamahamotorsports.com/assets/service/manuals/0/LIT-19626-01-23_1423.pdf

Make sure the generator breaker switch is flipped on to allow voltage and amps to flow to the recepticals. Otherwise, if the switch is on, then you have overloaded the generator and blown a capacitor, resistor or similar item and the gen needs to be serviced.

The toggle switch automatically resets all faults when it is turned to the off position. I would turn the toggle switch off, turn off the breaker on the generator and then turn off all the loads in the house except a few lights. Turn the generator breaker back on, then turn the toggle switch back to automatic. If it starts and stays running, you were overloading the generator. Turn on other loads slowly and keep track of what is on so you don't overload it again. If it still does not stay on, you may have a problem with the panel. Let me know what happens.

it may be a thermal coupler that cuts out when it gets to hot i would let it cool off for a bit then try it with a lighter load and go from there

Your generator does not have enough wattage to run an AC.

Well 20 amps at 120V is only 2400 Watts. So yes each recepticle can handle 20 Amps. For a total of 4800W Continuous. The head room Between that and 5500W is generally for starting motors and inrush currents.

Check a see if it is when the unit is starting up when the over load happens if so you need a hard start kit