RE:72 XL250
(Date Posted:08/09/2008 11:05 AM)
My XL250 Motosport when I rode it on the road back in the 70's used to do about 75-80mph in top on standard gearing, revving approx 8000rpm. That was standard gearing (15/48? front/rear sprockets). It would cruise around 60-ish and get about 60mpg. I can understand your anxiety about 'pushing' the motor but I think once you get used to it, you might be happy running a little faster than you do at the moment.
I did later put in a Yoshimura high-comp piston and Stage 1 cam and (ahem) slightly less restrictive pipe (no silencing - for a while, until my ears started bleeding. Also, it attracted a little too much attention from the law.) It would regularly pull 9200rpm in top which was about 90mph, on standard gearing with a Dunlop Trials Universal tyre on (square profile but at least back then they were 4-ply so they didn't squirm like modern 2-ply trials tyres!). It pulled wheelies on the throttle and clutch in 1st and 2nd gear (and you could carry on in 3rd,4th and 5th if you were standing on the passenger footrests!).
At the point when the main bearings started rumbling prior to the Yoshimura parts, I deliberately ran the motor as hard as it would go - and I remember distinctly seeing the revcounter heading up over 11,000rpm - and it still never actually let go! In other words, it will probably be quite happy to rev a lot more than you think - it's just that they ain't as smooth as a modern single cylinder motor (unless you've spent a lot of money getting somebody to build you a race motor!). I think if you look at the XL Page, there is a Powroll spec sheet which shows their flat-track motor as running to 13,660rpm and they don't do a great deal to the bottom end to keep it together!
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