I used to own an RGV250, ran it for around 6000 miles. Never any problems with the power valves, but it did melt a piston. That was my fault, being young and foolish, ran it on cheaper semi-synthetic oil - oh dear! Other than that, it never missed a beat. It was always at WOT because I was riding with mates on GSXR / ZXR 750s at the time. Didn't do any home tuning though, probably what saved me from more destruction
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Rich
MC21 Track Bike / RS250 NF5 'Spencer', NX5 'Cadalora' & NXA 'Aoyama' / RS500 / Two Brothers Racing RC30