I have a 1991 yamaha dt50mx with a big bore kit, full gianelli exhaust system, i am going to get a k&n filter for it and racing reeds. I was wondering which jets in the carburettor i will need to change?

Thanks

Bigger main jet.

In the old days we had a Ledar air corrector kit, that came with all the parts needed to run K&N or S&B filters and expansion chambers. Some bikes needed an extension tube between the carb and the filter as well, but I don't know if your bike is one of them.