[uncledunnie]

thanks for that chaps,

I fairly happy with the little bike and the price, but......

I do have one remaining concern and this point is really directed at the rule makers.

The regs state no work to the cyclinder heads, but I can go to the big bore conversion - so if I do buy the bike I know I will want to go big bore so does that mean I'm stuck with the 600 heads?

These things have tiny valves and because of their design I understand that fitting larger valves is virtually impossible / expensive. If I'm correct from the info I have gathered the 600's biggest drawback to performance enhancement is inability to suck air - due to the restrictive valve arrangement, so.......

1. In doing your calcs re performance balancing between the big 600's and the 620's can I change the heads during the conversion? If so what are the regs regarding that?

2. If I cannot change the heads on conversion I assume the figures you have been working to mean a larger bore 600 with stock 600 heads will match a 620 with some simple carburation mods.

Perhaps the powers that be could clarify that one for me.

I'm becoming a bit sceptical that an overbored 600 with stock heads and cams and free exhausts will match a 620 with free exhausts and fettled fueling.

600 approx 50bhp stock Vs 620 63bhp stock, I could see a 620 going to low 70's quite easily but a 50% power gain on a 600 is starting to look a bit optimistic in my eyes.

Any one put my mind at rest, I can't see the point of forking what looks like being the best part of £3k on a 600 with overbore and other mods to find its not competitive (rider ability excluded!) against a much cheaper to modify and easier to sell-on 620.

Any one else had thought along these lines?