After hours of fiddling and fettling, and invaluable help from Co-Built's Antony B, I took my bike to Fiskerton practice track, dropped the 44mm Mikuni's main jet from 300 (that's always been in there) to 270 and did a few laps. Felt good. Checked the plug, nice colour. Did some more laps, couldn't get it to play up, but still didn't know if it's because I wasn't revving it hard enough. Still, I was going as fast as I could, so I could've raced and been ok. Boastie took it out, and except for hating my rear brake lever, he declared it 'Sweet'. Still, I won't be 100% confident until local dyno experts BSD have tested. It's booked in before the next race.
Thanks for all your advice fellas. GI
gary - i'm very pleased for you - BUT ! how come the 300 jets suddenly became wrong and 270s do the trick ? Could be the 300 is worn in which case replacement like for like should be fine ? if you stick with the 270 then you need to keep an eye over-heat. If you get back to where you were but on 270 then something else has changed - and I'd want to know what it is. When you're on the dyno, try a new 300 as well so you have a reference.
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