hello, i took the heads off my 1.3l engine and found out that the exhaust valve on cylinder #1 had burned really bad, replace it and on the reassembly i found out that the exhaust port stud was replaced in a bad way and it restricting the flow for about 20-30%, could that be the reason for the burned valve or maybe a wrong rocker to valve clearence?

I would guess more it was a tight valve / over heating.

A vacuum leak some where could also make it real lean and there for run hot

A mis aligned exhaust stud would cause a backfire if it wasnt seating properly

Yes, sounds like incorrect rocker valve clearance... ie. no clearance..
adjustment was needed.. valve may have been open all the time...
thats why VWs need to have their valve rockers adjusted frequently... some people do them every oil change or 2...
cheers
Lee

Could of been a leak on the outlet manifold somewhere !

nIck