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Truenotch's 1974 Yamaha FS50 (FS1)


Truenotch

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12 hours ago, BLIZZO said:

fizzy would look cool with a small steel guard mounted moto spec, ie - on the underside of the bottom triple clamp. thats what im in the midst of with my CB50 as i got like the no front guard look in it

 

Yeah, I'm thinking either a small steel moto guard or a minimal wheel fender. The headlight and speedo also need to be moved down a fair distance... It's hard to make a pressed backbone body look tough IMO. Regular frames are easy to make angry. 

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  • 4 months later...

I’ve been ignoring this thing for a while, but am sick of it being in pieces in the shed. 

I needed to replace the piston after East Cape and decided to give it a quick hone beforehand.... but after a series of screwups that I’d rather not discuss, the lower skirt of the cylinder is now broken beyond repair. Note: cast doesn’t bend. 

After all that I decided that I wasn’t happy with the Chappy style cylinder anyway. The transfer ducts were too much bigger than the standard FS1 ducts which would have caused some strange flow. It used to rev better with the original cylinder anyway, so I’ve decided to go back to an FS1 style cylinder. The biggest available at the mo is 43mm/60cc, so that’s what I’ve ordered:

69226479-D513-4249-8088-8B3FF4F58730.jpeg.09c2291637dcca505fe63be52c091bca.jpeg

But I didn’t want to throw all my good parts away, so decided to make the Polini carb fit up to the standard manifold. The standard carb fits a 20mm sleeve and the Polini hole is 24mm. Enter @Geophy who spun this up for me: 

20273497-6179-4555-AC17-EDCAE2C2EA25.jpeg.a58f3258300e5e3786c1bba7f0a7e394.jpeg

Threw a couple of slices in one end so I could clamp over it. The clamp is chopped off an old carb. It works a treat! 

6E9B1F0B-A9D2-4B01-A7B6-2D40423A8E91.thumb.jpeg.d5dff0091b186f359f04a14ec9d4b048.jpeg

Carb goes here:

F6B3A240-9C11-40CE-8AE7-07F2C6BD2149.thumb.jpeg.2671a75905d5bf024c47e62861c86dc6.jpeg

It pokes out the side, but that’s life when you put a big carb on an FS1! I’ll have an air filter just above my brake pedal but i think there will be enough clearance. 

C201019A-445C-4DAC-85BD-FBD0CC607725.thumb.jpeg.c68134ef4622f2242978a425252bdd90.jpeg

... I might make some sort of cover to tidy it up later, but for now, it works. 

All this means I’ve got empty space above the engine again. I’m thinking if re-fitting the OG filter housing and using it to hold a tool kit and spare spark plugs. 

1FD7C801-4463-4FB3-AAF2-272C96C78007.thumb.jpeg.25e021b77c246ce9aba39c4c5c529771.jpeg

 

Now to wait for overnight parts from the UK! 

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Choice ya getting back into it mate. Rode my F5 the other day and forgot how much I love my two stroke.

Plus 1 for using that as a tool kit. Also throw the battery in the bin and run a trailtech regulator and then you free up all that space for beers 

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6 hours ago, Chris.QCR said:

Choice ya getting back into it mate. Rode my F5 the other day and forgot how much I love my two stroke.

Plus 1 for using that as a tool kit. Also throw the battery in the bin and run a trailtech regulator and then you free up all that space for beers 

Did the YB100 motor bolt straight up to your bike? I’ve bought one but the mounts are wider than the little 50. 

Already ditched the battery and added a Trail tech :D . 

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Mine bolted straight up aye. Mish mash of cables between the the yb motor and F5 and it the wiring was plug for plug and I used the stock yb100 pipe with baffle removed. Stock I could get 110km out of it with me and all my camp gear

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34 minutes ago, Chris.QCR said:

Mine bolted straight up aye. Mish mash of cables between the the yb motor and F5 and it the wiring was plug for plug and I used the stock yb100 pipe with baffle removed. Stock I could get 110km out of it with me and all my camp gear

That's sweet! 

I was pretty confused when I offered the 100 motor up to my frame... The mounts are about 10mm wider than the FS1, so not easily fitted without taking some meat off the motor or frame mounts.... Not worth it yet... 

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My parts turned up from the UK today. Time to get back into it. 

I’ve always had issues with clutch slip on this bike. They only have 2 friction plates so will never be great, but it also shouldn’t slip with every gear change... it’s not like it has a lot of power. I’d previously changed everything in the clutch system: plates, actuator rods, ball bearing, clutch arm, cable, adjuster, upgraded to fancy 2 stroke gearbox oil (when plates were new) None of those made an ounce of difference. 

There are some in depth tutorials online about how to upgrade to 3 plates, but that requires precise milling and I cbf. 

Then I remembered that the only thing I didn’t replace was the springs. So I decided to upgrade them to MX100 springs which are a bit heavier: 

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Original on the left, MX100 on the right. 

Hopefully this will work. 

The new cylinder kit was pretty roughly cast. It makes me appreciate the quality of the Polini cylinder that I had before... but oh well. 

This is what all of the transfer ducts looked like - some had dags hanging from the walls too. 

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They looked gross and restrictive, so I busted out the dremel for a bit of a tidy / open up. 

Heres the front inlet duct after a bit of roughing out: 

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I did more shaping a s smoothing after this, but didn’t get any pics. I also opened up the exhaust port a bit inside the cylinder and gave all the ports a good chamfering. 

All going well I should be able to test run it in the next few days. 

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Another successful night tonight. I got the cylinder finished up - the ports could be better, but it’s a good starting point. 

Checked the ring gap and re-installed the cylinder. Then I threw the motor back on and oiled it up. Amazingly it fired on the second kick!

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My expansion chamber still needs love after the beating it took on the east cape, so I threw a standard exhaust on from the YB100 parts stash. Amazingly it fits! The only difference is the silencer is about 100mm longer than the fizzy unit. 

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Threw the old style plate on to see how it looks:

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Love these 12 hole plates. 

Took it for a quick hoon up the road in the dark and it’s definitely seems like it’s running rich. I’ll play with jetting this weekend. 

I also remembered that I’d gutted all the wiring from the hand controls... which meant that I had no lights! No decent test ride tonight then... I spent some time figuring out which wires are supposed to go to the lights as the pre and post switch colours are different. I got there in the end and now have working tail light, brake lights and will have headlights as soon as I crimp a couple of connectors to join some wires. 

Does anyone know if the high beams are usually both filaments running together? I don’t have a dip switch anymore, so want it to be high beam all the time. My headlight is a 12v 25/25w. Can anyone see a reason why I shouldn’t power both 25w filaments together?

 

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