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Classic Bike Trackdays

YZ/RD 80 Race bike

 
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Dave B



Joined: 24 Oct 2019
Posts: 15
Location: Staffs Moorlands

PostPosted: Sun Oct 27, 2019 10:14 am    Post subject: YZ/RD 80 Race bike Reply with quote

This is my 80cc race bike in its final configuration. It has a YZ80 engine, a cold air box for the carb, an MBA fairing and a CBR600 front brake. At the time I was making computer designed exhaust pipes under the name "Two-Cycle Developments, so it was my own exhaust. It was not quite a match for the genuine GP 80s like the Huvo or Kreidler etc. but it was a great little bike to ride. The cold air feed to the carb meant that it was as fast on the last lap as on the first- which was not the case of many of the competion. It was a shame when the 80cc class ended, though the GP bikes were still very competitive in 125cc races, the motocross engined ones weren't. So i sold this and for a short time, rode a 500cc four stroke single.
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James P



Joined: 31 Mar 2013
Posts: 184
Location: Sydney, Australia

PostPosted: Sun Nov 03, 2019 6:52 am    Post subject: Reply with quote

That looks interesting Dave. Have you any more photos of the bike? Was the engine all standard apart from the pipe?

I haven't followed bike racing for ages, but understand there is now (or was recently) a class for 80cc bikes, most of which seemed to use RS125 or TZ125 chassis with motocross-based 80cc engines.

Regards,
James
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Dave B



Joined: 24 Oct 2019
Posts: 15
Location: Staffs Moorlands

PostPosted: Sun Nov 03, 2019 9:10 am    Post subject: Reply with quote

Hi James,
I seem to be constitutionally incapable of leaving things standard, so I can tell you that there were a lot of changes to the porting. To some extent I was a bit ahead of my time in that, even without the computer simulations we use these days. The exhaust port was reshaped, but not significantly enlarged. There was a lot of work on the transfers, especially on the radial and axial angles. The plan was to increase the blowdown time area, which was not the way that tuners mostly worked at that time- and which was shown to be the best approach when the simulation software became available. There was a six-petal reed from the 125MX bike, and I used a 32mm magnesium carb from an RG500. Ignition was the standard MX- not what I would do today! It was quite hard to get a spark plug that would run reliably in the races, so one day, having fouled my entire stock of race plugs, the only plug left in the spares box was an old pink Lodge plug that I carried as a souvenir, because Barry Sheen gave it to me. I fitted that and it ran prefectly for the next two seasons. I loved the 80cc class. Everyone was really friendly and fiercely competitive on track, and you could put a competitive bike together for not much money. It was a great shame that it was stopped. I'm convinced that there is a very great deal to be learned from riding tiny machines, conserving speed, maximising power. You will never learn that on a heavy road based bike with 100 HP.
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emzedder



Joined: 15 Dec 2006
Posts: 324
Location: E.Anglia

PostPosted: Sun Nov 03, 2019 5:45 pm    Post subject: Reply with quote

Always been a big fan of small capacity racing since I saw 50's at Silverstone GP in the 80's and later Ian McConnachie on the 80's. ... a much unrecognised rider these days. The challenge of extra HP and tucking in , slipstreaming and keeping up corner speed seemed to have it all. I much admire this., great skill required.
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