I have a 20hp honda GX620, V-Twin. It powers a boat. I started it the other day and it ran perfect. I tried starting it today and it wouldnt start. I took the air filter off and put my hand over the intake. It started up and would only run if I would periodically cover the intake. I could keep it running as long as I did this.I checked the gas filter and it appeared to be letting gas through. I checked the plugs and they were firing fine.The choke appears to be working properly. It will not stay running for more than 10 sec without me having to cover the intake and then taking my hand off. :confused:
Is it starved for gas or what?
Thanks ahead of time for your diagnoses!

I have a 20hp honda GX620, V-Twin. Is it starved for gas or what?

Yes, it is being starved of fuel. Since it is a 4 cycle engine, I would say that you have one of two problems....either you have a clogged spark arrestor (which I seriously doubt), or you have something clogging the carb. If I had to bet money on it, I would say that the carb is the problem. More than likely you have a little piece of dirt or a little bit of water in the bowl of the carb that is keeping it from running right.

What you need to do is pinch off the fuel line or relieve pressure on the fuel pump and take the fuel bowl off the carb. Clean the bowl out well with carb cleaner and spray some carb cleaner up through the pickup tube and jet. Try not to spray the rubber gaskets or seals too much because carb cleaner will make them swell up. After you get everything nice and clean, put the bowl back on, reconnect the fuel lines or fuel pump (whatever you did to keep fuel from flowing in the carb while you had it apart), and see how it runs.

Thanks a million. I'll break it down and clean it.

most likely since its a boat the carb bowl has water in it. i had one idiot left his mower out in the rain all the time wouldn't start or run very long. had a half a bowl full of water in it. and it stopped the float from floating and left it in a upwards position.