Depending what the bike is set up for I would run avgas.

Of course you will need to check what PGM and fuel coupler is fitted as well as the cylinder heads. As on the RS's though the heads are easy to pop off and measure the squish and volumes.

There were 3 types of pistons and to run the leaded you really need the late piston with the semi key stone rings and domed head or the very early '97 piston with a standard ring.

We are running the 1999-01 pistons with the "C" heads with 23.6 and 23.8cc volumes (not including the plug). '99-00 PGM's with the a leaded coupler.

There are also different reeds and stops for unleaded and leaded set up so it's worth popping them out and seeing what you have fitted.

What fuel was the bike running on before?
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If I have to take the carbs off once more...