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Good news is that all the suspension work has paid dividends. Taupo is a fairly tight and technical track and the FZR felt like a different bike to the tank of a thing I rode there last year. Qualifying and first race went OK (I wasn't last!), a good time was had and I took five seconds off my personal best lap from last year.

Bad news was the second race. It was a long one (20 minutes) which rather showed up my lack of match fitness, and the FZR also struggled a bit, feeling like it was losing power a bit and finishing the race with a distinct rattle on the overrun - camchain perhaps? Time for some attention I think, that motor has done a few miles now, most of it on the limiter. Second ace results weren't good - what I said earlier about getting a good look at the fast boys as they came round to lap me - but engine woes aside I still ended up reasonably satisfied with the day. I wasn't the only one struggling, there were two blown Gixxers in the pits by the end of the day.

Something I did note, especially after the second race, is that the motor is almost impossible to restart in the pits after the race. I think there are some serious heat soak problems which could well be costing me power. Something to have a look at when the new motor goes in - need to get lots of cooling air in around the carbs and some shielding/insulation above the motor.

Sounds like you have a sensible idea of what went wrong, and the two problems could be related? Could the rattle be preignition because the
mixture is evaporated?
Difficult starting, especially when hot, can often be a sign of valve clearances
being too tight, especially on yamahas. When I worked in a Yamaha shop it
was the boss's rule, if difficult starting always check valves first and 9/10
times the valves were heaps tight.
Glad to hear the handling is a big improvement!

I didn't think about valve clearances but you may well be right - lack of compression when hot and possible preignition. The valves haven't been checked since the motor went in so worth a look.

I think the noise is mechanical, its a sort of big rev then clatter,clatter, clatter on the slowdown. Its not loud but it is consistent. On a road bike you can hear the camchain at idle but idling is not something my engine likes to do much, especially when its hot, so kind of hard to tell.

Five seconds... That's huge

Glad to hear you survived, and hope the engine is an easy fix. Keep us posted. Cheers.