type of fuel

1983 1.8 gti leaded or unleaded head from the factory?

Unleaded, all VWs had hardened valve seats very early on  but runs best on Super Unleaded rather than just regular

Vw water cooled engine from 1974ish will run unleaded petrol, use super unleaded if you can as then the timing can be set up "by the book", you need to retard the timing the run normal unleaded.

cheers lads I have been putting super unleaded in it just in case, ' asked our kid who worked on these all the time when he was a mechanic at lionel smith's in manchester and you've guessed it he didn't have a scooby. by the way Richard it's a mars red campaign with a nice body & trim but quite a few mechanical issues
 

just use standard unleaded super makes noticeable difference to the performance