Bad Naughty SVX 120 miles to tank

[down under]

Hi i am a newby to site and have a 1993 SVX with 120000miles [200000klms]
I have done all the usual SVX things new g/box,radiator,discs etc etc but i am now getting this redicules fuel economy. The only authorised SVX dealer in South Oz [australia] is not so good and my local mechanic who is good but doesnt have the computer to read my cars codes tells me that it is running the right 02 read outs at exhaust but maybe a fraction rich at above 4000rpm a place i rarily get to [bugga] has anyone had these problems and if so what did they do to fix it is getting expensive filling this car with premium 2 plus times a week. I lied about newby i have been reading the forum for a year but not posted as the answers usually stacked up but i havnt found much related to this one yet.