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Hello folks,
so I have gotten a Yamaha EF600.
At first, it didn't run at all as fuel leaked from the fuel pump/cock located under the gas tank that pushes gas up to the carb, and cycles back to the tank. I cleaned the pump, as it was totally blocked, afterwards no leaks were to be seen and it cycled gas just fine.

But when it runs, at moments, every few sesconds the RPM (voltage with it) drops and I lose about 20-30V and it doesn't if under load or not. This can be noticed even when connecting a simple light to it as it flickers noticably. Also happens without load, but this time the voltage rises up to 240VAC but still drops down,

As I got it with really old fuel that stood a long time, I took our the carb, cleaned the bowl, the big screw with the hole holding the bowl, the main jet in the middle (one that looks like a flute). Overall it was very bad as most of the hols were stuck shut. Closed the carb, put it back on and the issue still isn't resolved and I'm out of ideas. The gaskets at the garb do seem a little thin to me, but definetly not broken. Sparkplug is like brand new. It's a bit more noticable when engine is hot.

Also put in fresh oil. Does it matter if my air filter is oiled or not? As I read somewhere that it actually has a meaning to it.

Thanks anyone in advance! (see video)

If you are mechanically inclined I would purchase Service Repair Manual & make repairs. Otherwise I would call a Yamaha Dealer in your area & ask if they can service & repair generator. Have Model & Serial numbers handy.

mechanic mark said:

https://www.google.com/search?q=MANUAL+FOR+EF600+YAMAHA+GENERATOR&oq=MANUAL+FOR+EF600+YAMAHA+GENERATOR&aqs=chrome..69i57j33i22i29i30l9.41070j0j4&sourceid=chrome&ie=UTF-8

If you are mechanically inclined I would purchase Service Repair Manual & make repairs. Otherwise I would call a Yamaha Dealer in your area & ask if they can service & repair generator. Have Model & Serial numbers handy.

Click to expand...

Thanks for the answer, but sadly not possible.
Literally no Yamaha dealers in my area, or even remotely close. Also, if there was one, I hardly believe they would repair a generator from the 90's. Buying the manual is more than what the repair is worth. Thanks anyways!

Have you tried running it with the gas cap loose? air needs to get in for fuel to get out.
also will it do it if you choke it a little bit?

More questions than answers. Do you have a tachometer and VOM? Is this generator just 220-240 or do you have 120VAC outlets? Is this a constant throttle unit or one that idles down when no load is applied? Working on generators requires a knowledge of both how the engine works and how electrical components works, along with how they work together. You must get the engine to run properly, then adjust the governor to obtain proper voltage output. Your VOM should also have a hertz setting for adjusting the governor.

Cheap enough to purchase a meter meant to monitor cycles and voltage off Ebay or Amazon. I purchased one, mounted in a box on my Onan 30kw, just requires a 18 ga wire from the AC out to gauge.

Order you a cheap chinese carb off Amazon or Ebay. Get the number off your carb and also compare the pictures closely, make sure the air cleaner mount and linkage are the same.

Hey and thanks anyone for the given help

At the end, it was the air filter I put in. It isn't the original one, so issues were expected. As it was too thin, the air/fuel mixture was wrong and governor went nuts all the time. I added more filter material, dipped it into oil and adjusted the idle and governor, and now it runs really nice. Sure, not perfect, but it handles the load pretty well and the light doesn't flicker as much as it used to. Throttle is also calm. Sorry for the late reply, I was busy.

I hope you measured output voltage under load when you adjusted the carb. If not please go back and do so. If the voltage and hertz are not close to specs, you could definitely burn up equipment by not having it close to specs. Just because the engine sounds good, doesn’t mean the generator is set properly. I’ve had more than one contractor burn up expensive power tools because the small engine mechanic didn’t know that this should be done.