Yamaha hs1 90cc twin clean up

Mail came today, so I can start to reassemble. New base gaskets, bowl and needle seat gaskets, crank seals, front pads and un molested slides.
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Here is the comparison with the un cut slides.
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My guess is that the p.o. saw that at WOT the slides do not clear the through opening, thus shortening them to clear. Also, just a guess is that this model carb may have been used on a larger cc model bike, and the slides were changed for this model specifically to restrict air flow. Anyhow, I'll put the new slides in and see if the Japanese engineers knew better than the old farm boy lol this may be where the lean symptoms were coming from that made me suspect a need for crank seals as well, so before I split anything, I will replace these slides and see what I've got.
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Going back together.
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One of our neighbors owns a scrambler version of this bike. It's almost jewel like, unfortunately it has sat too many years. His sons robbed parts off it in the 80s. I gave him a kickstarter to see if it would turn over and much to my surprise it did. Unfortunately, he thinks it is very valuable and is going to get big bucks when he sells it.
 
Got the rear end cleaned up and back together.
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Pipes cleaned up really nice. A few small dings, but almost perfect otherwise.

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And she is a runner again. Stock slides fixed all the problems. Found out that the guy had this thing to a bunch of different shops back in the day, and they never could "get the carbs fixed right".

https://youtu.be/nO5AWzKArcg
 
Outstanding ride! Love the little twins.
The longer slides were probably Yamaha Motor Company's attempt to restrict the power of the bike - I've seen something similar on the X7 Suzuki 2 stroke twin that was sold in the UK in the '70's. Probably makes your bike act like it has 10 mm carbs LOL.
You can find out first hand yourself how greatly the power is restricted - put the long slides in, ride the bike and then put the short slides in and try them. Let us know what you find out.
You're probably right, to leave the bike stock as it is in such exceptional unrestored condition but ... if you could find another set of cylinders and heads cheap and do Yamaha Racing Papers mods on them and ... use YJ2 pistons and make it 122cc (the YAS1 pistons or even TA125 pistons might work as well as they all have the same pin diameter), well, my, my, my...
Thanks for sharing and have fun with your ride.
Pat
 
pacomotorstuff said:
The longer slides were probably Yamaha Motor Company's attempt to restrict the power of the bike - I've seen something similar on the X7 Suzuki 2 stroke twin that was sold in the UK in the '70's.

This is the reason. I remember shortening slides at my uncle's Yamaha shop back in the 70's. It was all about complying with license or insurance horsepower restrictions in some locales a particular model was sold.
 
Lookin' great! Just like what I learned to ride on (in addition to the mini bikes) and what I took my MC driver's test on. My brother bought the thing but I think I may have put more miles on it than he did.
 
pacomotorstuff said:
Outstanding ride! Love the little twins.
The longer slides were probably Yamaha Motor Company's attempt to restrict the power of the bike - I've seen something similar on the X7 Suzuki 2 stroke twin that was sold in the UK in the '70's. Probably makes your bike act like it has 10 mm carbs LOL.
You can find out first hand yourself how greatly the power is restricted - put the long slides in, ride the bike and then put the short slides in and try them. Let us know what you find out.
You're probably right, to leave the bike stock as it is in such exceptional unrestored condition but ... if you could find another set of cylinders and heads cheap and do Yamaha Racing Papers mods on them and ... use YJ2 pistons and make it 122cc (the YAS1 pistons or even TA125 pistons might work as well as they all have the same pin diameter), well, my, my, my...
Thanks for sharing and have fun with your ride.
Pat


hdscarbro said:
This is the reason. I remember shortening slides at my uncle's Yamaha shop back in the 70's. It was all about complying with license or insurance horsepower restrictions in some locales a particular model was sold.
I'm sure this had much to do with it, and there is almost undoubtedly gains to be had by shortening the slides, but to a smaller degree than the p.o. had. When I rode it prior to disassembly, with the slides cut in half, it would fall flat on its face at WOT, I think due to an excess of air. The slides were literally cut in half. Also, it would not idle down, due to there being a gap at the top of the slide. In stock form, on the bench, it idles beautifully, and doesn't hesitate through the revs. Hopefully later today I will be able to buzz around a bit and see how it does under load. I would think there is a plateau to shortening the slides, and would have to be done in slight increments to find the sweet spot, where the p.o. just cut it in half. Also, I'm a little hesitant to cut them, as they were the only correct slides I was able to find, and once they are cut, I do not know if I can find another set.

I was actually at my favorite local mc salvage yard yesterday, and the guy had a nos high performance Yamaha top end for this bike. Aluminum jugs (vs these cast iron ones) with chrome plated cylinders. They were sweet for sure, but he valued the setup at $600, which may be fair, and I'd be tempted if this were a keeper, but as its a flipper, I would not see a return on the investment. As with any stock two stroke, there is gobs of power to be had over stock design, but on this bike I plan to try to stay on the side of dependability, and hope to not sick a piston before she sells ;)
 
ridesolo said:
Lookin' great! Just like what I learned to ride on (in addition to the mini bikes) and what I took my MC driver's test on. My brother bought the thing but I think I may have put more miles on it than he did.
That's great Cory! You should come buzz around the block on it before I sell it to relive your glory days! I'll jump on the gt250, and we won't have a mosquito problem in Grandview for weeks!
 
Well, got at it early and pretty much finished it up this morning. Front end cleaned up and re assembled.
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I guess this is a pretty anti climatic deal, just lots of elbow grease, de greasing, some maintenence and polishing. Still a little carb tweaking to do, she stutters a bit at wide open, but full slides made a big difference.

Anyhow, she cleaned up nice, and is ready for a new home.

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adventurco said:
Well done mate. Looks like a fun little smoker


Sent from my iPhone using DO THE TON
Ha, I rode it for a bit today. Hit 42 mph with a tail wind. It is a neat bike, but it's time for a new home lol
 
hurco550 said:
That's great Cory! You should come buzz around the block on it before I sell it to relive your glory days! I'll jump on the gt250, and we won't have a mosquito problem in Grandview for weeks!

Good chance I'll trot on down this afternoon and check it out... you never know, my brain bucket may mysteriously find its way into the truck before I head out. 8)
 
ridesolo said:
Good chance I'll trot on down this afternoon and check it out... you never know, my brain bucket may mysteriously find its way into the truck before I head out. 8)
Ha she may not so be here.... may be on its way to a new home already...
 
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