Sr 643


They attributed the Yam 433 winning over the Doo 800 as being due to much better handling. He would pass the Doo while entering, going thru, and exiting the corners. Oh, and it was a lot better looking... ( I may have made that last part up)
 
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SR's

In the article, Mike Trapp said that the early machines, Yamahas, were ill handling, and you can certainly see that compared to the 73 SR's. But looking at the doo, it really wouldn't take much there! They had their engines mounted up high on the tunnel like the Yamahas, but even at that, they looked so narrow and awkward compared to just anything else.

Polaris and Arctic Cat were the first ones to have the engines mounted down low over the ski's, something that is very apparent in the photo. Polaris was actually the sled that was consistently in the winners circle in those days, but while Yamaha was new on the scene, they brought along considerable experience in two stroke engine technology from their motorcycles. So well their chassis was behind, their engines were not and surprised the rest with their strong performance and reliability. Well, save for some early teething problems like the aforementioned crank problem. G.
 

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You have to wonder what the guy on the Poo is thinking when a guy pulls up beside him on a sled half as big. LOL!
 
I have a question, perhaps one of you vintage race guys can answer, Monty? What are those 'scissor' things on the skis of all or most of the vintage leaf spring race sleds? I'm guessing they assisted with the sideways flex inherent in leafer suspensions and probably had some resistance set into them for rebound damping, correct?

I've never seen any, other than in pictures, or seen them mentioned anywhere? What are they called? Anybody? G.
 
Gorkon said:
I have a question, perhaps one of you vintage race guys can answer, Monty? What are those 'scissor' things on the skis of all or most of the vintage leaf spring race sleds? I'm guessing they assisted with the sideways flex inherent in leafer suspensions and probably had some resistance set into them for rebound damping, correct?

I've never seen any, other than in pictures, or seen them mentioned anywhere? What are they called? Anybody? G.
Click to expand...

You got it. they help to prevent the spring from twisting/rolling wich can allow the ski to roll under the spindle slightly
 
RICKYAMAHA: I just accidentally found all the microfish for the 72 SR 643! Go to this link and search in 1975 snowmobiles. http://www.powersedge.com

It is there listed as a 75 and not in 72 for some reason? But it's all there! If you don't already have this, you may want it as it gives details on every part so you can see how it goes together. I've attached one of the slides here. Enjoy, and keep us posted on that assembly. Pics would be nice too! G.
 

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Wow! That girl has seen better days, but then how many did he say were in the registry, four!!! Someone's obviously been trailriding it at some point. Still curious as to how many were made and am inclined to think that the number of 73's is a pretty good indicator. I hope someone saves this one though, my plates pretty full. G.
 
boy if i did not bite off more than i could chew with buying a bunch of sleds already i would surely of loved to of landed that rare beast!oh well!
 
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