Yes PTFE tape should be ok with petrol, be sure to wind it on in a clocwise direction when holding the thread with the left hand. Why not buy a new item and regard this as a temporary fix.
If it is an air mixture screw, ie on the filter side of the throttle slide, then screwing it in will make it richer
However, if it is a fuel mixture screw, ie on the engine side of the throttle slide, then screwing it in will make it leaner
Hi Paul nice to hear from you, that bike really does look like a lot of fun and you got it for F-all...nice, see what you mean about the mirrors tho...Gawd
There are only two adjustments that you can make from outside the carb. The idle screw ( Throttle stop screw ) adjusts the speed of the idle. The idle air screw adjusts the idle mixture. This is only at idle and does not effect anything above idle. Here is another method to adjust it. Screw the air screw in and out until you get the highest idle speed. Then lower the idle speed with the idle screw and do it again until you get the best idle.
If you can't get it to idle, or rather the idle stays real high then drops off and dies, check for an air leak at the carb manifold. Squirt some gas or starting fluid on the manifold and see if the revs change. If they do, you have a leak. If your valves clearances are too tight, it will also effect the idle.
Yorkshireman wants a headstone making for his late wife, and he asks the mason to carve 'She was thine' on it.
When he goes back a week later the headstone reads 'She was thin'
"No you idiot" he complains, "you've missed the 'E' off"
So he goes back a week later and looks at the stone, which now reads ......
'E she was thin'
A bloke from Yorkshire goes to the jewellers:
He says, "Can tha mek a gold statue o' mi dog?".
"Aye, reckon a can," sez the jeweller.
"Does tha want it eighteen carat?".
"Neigh," sez bloke, "I want it chewin' a bone."