I have completely rebuilt the petcock but I still have a serious gas leak. Can you help?

Either the gasket/o-ring that seals the petcock where it screws into the tank is bad, or the petcock needs new seals/rebuilt (there are kits for this), or you could just replace the petcock.
You need to get down there and see where the leak is actually happening.

Considering the age of your bike the vacuum valve on the fuel petcock may have failed. The vacuum valve uses vacuum from one of the air intake manifolds to allow fuel to flow only when the engine is running. But if the valve develops a leak, it fails to open when the engine is running. Some valves can be rebuilt, others require changing out the entire petcock.

MGM

recheck and clean /adjust floats pet **** doesnt stop fuel in bowl if floats out of adjustment or valve sticking/debris will allow fuel to constant flow

Not sure if this will fix your problem but.... we had a 454 LTD with a leaking petcock. we had to replace all the seals and rings in it. stopped the leak. not sure if honda still makes parts for that old of a bike, but kawasaki does not and getting a new petcock was not an option.

How about the flexible rubber lines? Are they leaking by any chance at the points where they join at the ends?

Thank you for contacting FixYa with your KTM inquiry.
This happens sometimes. Usually it's one of two things:

• You forgot to turn the gas lever off under the tank (Petcock).
• The float valve stuck in the open position and allowed gas to drain out of the open petcock.

Bikes bounce around quite a bit sometimes mounted on the trailer on the trip home and if the petcock is open this happens. Sometimes the float valve sticks open. Noting serious just smelly and annoying and gets you in trouble with the wife. Tap on the float bowl with the handle of a screwdriver and it usually will shut off.
Hope this helps.
Kind regards,
TF

it sounds like you petcock vavle ( your fuel shut off valve) is the problem its easy to change i would really keep a i on it no fuel leak is a safe thing to have.

Hello check your engine oil level to see if it is over filled.
Also if it is smell it to see if there is gas in the oil.
what some times happens with older motorcycles the fuel petcock o-ring or diaphram goes bad and fuel will weap into the cylinders and into the crankcase. raising the level and pushing into the air box via the crankcase breather hose.
Also check the vacuum line from the petcock if it has gas in it the diaphragm is leaking.

the only thing i can think of is that you might want to take the carb off and really clean it good where it bolts down and around the entire area if thats where its leaking from. Hope i was of some help to you.