i have a 1800 bus engine, with stainless steel valve seats and extractors, running on premium unleaded. what jet sizes should i be using? They are stock jets at the moment but have recently made the above changes.

you should not need premium unleaded,
your stock jets are probably about 130, if you hunt around dead carbies you may find some 132.5 which are standard in 2L, my standard 2L engine, I have had the jets reamed to 137.5 & find that ideal, I would recommend trying 135 where you live

I take it your running standard Solex carbies...

And i would take Bens advice and get it on an air / fuel ratio meter while the cars running.

yeah they are the standard solex ones. il try and chase up an air/fuel meter. thanks.

The fuel / air meter is about $2000.00 worth your better off going to a VW shop that has one and get it done there.

no worries. when all else fails leave it to the experts. i rang mike from CBB and he checked it last time it got serviced. it was fine.