I have a Honda EU6500IS Generator, Only one of the 2 plugs works. Would be very helpful if I could get both plugs working properly. Any advice or suggestions?

GCU internal failure or inverterunit internal failure.

https://www.manualslib.com/manual/2167496/Honda-Eu65is.html?page=58#manual

The two alarms simultaneous is questionable. My first thought is faulty control board but requires further troubleshooting. Check for loose cable connections and grounds.

As a test; check oil level. If oil level is safe, disconnect oil level sensor and see if problem goes away. If problem reoccurs, troubleshoot oil warning circuit.

I don't know.
The air gap isn't usually critical. It needs to be a small gap for best efficiency but must not be so close it will touch if expansion brings it closer at operating temperature.

The last air gap I adjusted was on a Briggs engine and that was 0.008", 8 thou which I believe is fairly typical for that type of application.

Alfred,

Try checking the float 1st. Much like it is done in this video (different generator but same princible.):

:)

The inverter signals the throttle motor, which is really just a small servo motor on the top of the carb. When the inverter senses more load, it increases the throttle to compensate.

I can't find a free download on the internet, most are Owner's manuals or are not for the exact model you want - I don't know how similar similar models are. You might try the following:

http://cdn.powerequipment.honda.com/pe/pdf/manuals/00X31Z376011.pdf (from Honda, EU7000is owner's)
Honda EU7000i Model Info Super Quiet 7000 Watt Inverter Generator Honda...

This is the shop manual for the EU6500is model ($44)
Honda EU6500is Generator Shop Manual
owner's for the EU6500is
http://www.freeproductmanual.com/honda-eu6500is-manual

Finally a link to the search results most of the were taken from
https://uk.search.yahoo.com/search;_ylt=A9mSs2tVBShVngQA_xZLBQx.;_ylc=X1MDMjExNDcxNzAwMwRfcgMyBGZyA2FsdGF2aXN0YQRncHJpZANyOTBfV1hQeVNvT0twcW5oS3NxWlFBBG5fcnNsdAMwBG5fc3VnZwM0BG9yaWdpbgN1ay5zZWFyY2gueWFob28uY29tBHBvcwMwBHBxc3RyAwRwcXN0cmwDBHFzdHJsAzMwBHF1ZXJ5A0hvbmRhIEVVNjUwMGlzQSBzZXJ2aWNlIG1hbnVhbAR0X3N0bXADMTQyODY4NjQ3NQ--?p=Honda+EU6500isA+service+manual&fr2=sb-top-uk.search&fr=altavista

You could try contacting Honda (relevant division) also; if they will provide the manual you want, it might be free

10.April.2015

The manufacturer would be an excellent place to start... and they have superb paper manuals.

Yuasa YTZ14S is what mine takes

i have the same problem with a new one ,take a peace of paper and cover the battery cover air inlet when it's running ,if your problem stops-it's the seal around the cover,a honda rep let the cat out of the bag,---jk