Fuel leakage through petcock

[Kijmpe]

I have a leakage from, I suspect, the little O-ring that sits on the plunger of my vacuum petcock.
It is from a J-model.
Overhauled the whole thing, first had the body in the US cleaner for about an hour, renewed the membranes and plunger but it keeps seeping through.
Overhauled the carbs too with brand new needeles and seats, also had them US cleaned but they also seem to seep through.
There is always some drop of petrol hanging on the carbs when the bike is parked for a while and there is a permanent smell of petrol in my workshop.
Getting a bit desperate now with petrolprices going through the ceiling.
I was thinking maybe the spring that holds the plunger in place is old and has lost a bit of strength.
Is it a stupid idea to stretch it just a little to give it some extra pressure?
Any thoughts her?

[barney01]

Yes to the spring stretch but its likely the O ring on the plunger is worn. Have a look here
https://youtu.be/qWNyvjaWfz8
This is how i solved mine.
If the tap is not switching off it will overfill floatbowls .
You can also convert the tap to bypass the vacuum circuit by blocking the holes inside so you have an on and an off. But you lose the reserve facility.

[Kijmpe]

Hi Barney, thnaks for your reply.
I have renewed the whole plunger including the O-ring and still it seeps through.
Will try to stretch the spring a little to get a bit more pressure on the plunger.
If that doesn't work I think I will go for the option to make it a "on-and-off" only.

[Kijmpe]

In the end I have polished the seat of the plunger with a small tapered polishing head made of felt.
The petcock now shuts off again.