I have a Generac 5000 Power Plus 10HP Model 09856-0 Series 401 4891. It works fine but the gas tank petcock leaks. Where can I get a replacement and for reference I'd like to get a parts manual for future reference & needs. John [email protected]

Generac should be able to advise;
https://generac.ordertree.com/

Model not found on Generac web site using model number or serial number.

Generac contact information on their web site to request assistance:

https://www.generac.com/service-support/contact-us/online-form

I believe you mean the fuel pump. They do fail and leak, so likely you need a replacement. Make note of where the 3 lines connect (inlet, outlet, impulse air) Also check for fuel in the crankcase (oil) and drain and replace if necessary.

check to see if gas running out of carberator also check your oil make sure gas is not in there if it is or fuel running out of carb replace needle and seat in carb check for cracked seam on gas tank also make sure fuel line not leaking

FRIST O FALL CHECK TO SEE IF THERE IS A SHUT OFF VAULVE UNDER THE GAS TANK SEE IF THIS IS OPEN ALSO HOW OLD IS THE GAS , DONT LEAVE GAS IN THE GAS TANK THE GAS TODAY DOES NOT HAVE BUT A MONTH OF SHELF LIFE. YOU MAY HAVE TO PULL THE CARB DOWN AND CLEAN THE BOWL AND THE JETS IN THE CARB ALSO START BY PUTTING FRESH GAS IN THE TANK

1. remove the hose from the carb and see if the petcock is shutting off the gas and if not clean, repair or replace the petcock.
2. look in the tank and see if it has rust in the tank even a small haze of rust as rust will cause the needle and seat to stick in the carb and make the gas leak. If the gas tank has a lot of rust it may need a tank rubber liner kit added or even a new tank to stop the leaking.
3. if the bike has been sitting for a while it may have trash in the fuel system(carb/petcock/tank). Rust or any trash can cause a leak. Properly clean out the carb and fuel system and add a new filter when done.
4. Improperly adjusted or bad needle/seat or float in the carb will cause continual leaking. Replace the needle/seat/float and adjust the new one when installed. Check your service manual for float adjustments.

Repair or replace petcock then...Lol
As leaking gas becomes mixed it becomes a dangerous item as a spark will set it alight.

20:1 that's 1/4 pint to a full tank of fuel.

It is possible that your voltage regulator is shot but before purchasing the volt regulator try flashing the fields first and make sure the brushes and rings are clean.

you could try a briggs and strtton dealer as they took over generac but think with it being a tecunseh engine you will have a big problem as that side of the company went under a few years back,sorry cant be of more assistance