Truenotch

Truenotch's 1974 Yamaha FS50 (FS1)

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3 hours ago, Chris.QCR said:

If you havent yet remove the entire exhaust system and burn off all the carbon build up as this will choke your engine alot. Alot of different ways to do it but I usually stand upright on a bare concrete floor and pour petrol down exhaust and carefully light it up and use compressed air to get super hot and to blow melting buildup out other end

how do you carefully light it up? I've tried doing it before, but was way too scared to chuck heaps of petrol on it, so didn't get super good results

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6 hours ago, peteretep said:

how do you carefully light it up? I've tried doing it before, but was way too scared to chuck heaps of petrol on it, so didn't get super good results

Last time I poured petrol in a line away from the pipe about a couple metres and light the line up. 

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Thanks for that. I haven't had much off yet, just the carb so far. 

It's got no baffles and is loud as fuck, so I'm unsure how blocked it'll be. That trick is always worth a shot though! It became a lot harder to start when I got home from the ride and gave a couple of impressive backfires, so there's definitely a few things requiring attention.

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On 6/20/2018 at 03:51, peteretep said:

how do you carefully light it up? I've tried doing it before, but was way too scared to chuck heaps of petrol on it, so didn't get super good results

 

Degreaser can flame thrower

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This old thing has a few demons for sure... 

I had it running and took it for a gentle doort up the road. It definitely doesn't run well. I suspect the points need a tickle up/CDI conversion. 

Then I decided to pull more bits off. Removed the cylinder, carb and reed block: 

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Yep, you heard right, reed block. I always thought these were rotary valve. This proves they're not:

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The eagle eyed amongst you will notice that there's only 3 cylinder studs. #4 was super loose and was able to be removed by hand. 

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Hmm... This seems short... 

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The stud had snapped at the thread at some stage. There's still a hunk of bolt stuck down the hole and the top part of the stud hole is pretty munched. Looks like it'll need a helicoil. 

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I also wondered why the footpeg was so close to the gear lever. Looks like it's been dropped in a solid fashion. 

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So I guess I'll try to bend it back into shape or remake it with fresh bar or tube.

I've also got @Raizer working on a 45mm kit like this to make it ~65cc. These ones have an inlet above the cylinder, instead of coming through the side of the crank case. This makes it easier to fit a different reed and bigger carb. 

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Here's a couple of badboy 45mm FS1s for inspiration: 

 

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Took the cover off and removed the flywheel to get a look at the points. 

The left hand coil has loose windings at the bottom... Anyone seen this before? I think it still works, but might give out soon I guess?

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Gave everything a quick clean up and set the points. There was so much crap under the sprocket cover! 

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Gets really good spark now :)

Also investigated the broken stud - I suspect it used to be the other way up and someone sheared the top off when tightening the barrel down, then flipped the stud over to pretend nothing ever happened... The thread is good inside the casing, so all it needs is a new stud and it'll be good to go. 

the next funny thing is that the clutch no longer actuates. Maybe cleaning all the crap out has dislodged an important piece of actuating dirt? I've pulled the cover off the other side and the clutch plates and pushrod look good, but the rod on the actuator side is solid as a rock and I can't get it to disengage at all. 

Maybe the little ball bearing that sits between the pushrods has escaped? 

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Got the clutch working again after some head scratching. It needed adjustment to get the actuator bearing closer to the pushrod. 

Had a good squizz around this side while it was apart: 

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And pulled it further apart to see what else is hiding:

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Underneath the bike you can see the shadows of it's dirty past... Man there's a lot of dirt in this thing!

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On 19/06/2018 at 23:17, Truenotch said:

It goes... Kinda... 

It runs OK, but doesn't pull very well and won't rev.

 

Thats pretty normal, those old 50s are woefully short of power.

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1 hour ago, SOHC said:

Thats pretty normal, those old 50s are woefully short of power.

It should be able to go well I think. There's plenty of reports of standard FS1s reaching ~90kph, so I'm hopeful to achieve that number with a few mods :)

Got the clutch side transmission cover sealed up and refitted. Also bent the foot pegs back to roughly the correct location. 

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I need recommendations for tyres. The current ones are OLD Ching Beys or something. I'd like a sportier option, like what's on @Horse25's RD50. 

It's got 2.50 -17's at the mo and I'm wondering whether a 3" / 90 would fit. 

Also removed the wheels to check the brake shoes. They're pretty glossy and old! I've ordered a new set from @Raizer

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Something tells me the rear brake lever isn't in the right place... It sits really high and quite far out to the right:

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Might need a gas torch to get it into the right place.

Current state of affairs:

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It's pretty amazing how much you can do on a bike with minimal effort. Last night I removed the engine to check a couple of things. This required removing ONE BOLT (foot pegs were already off) and undoing 5 wires.

I'd been trying to avoid removing the engine because it seemed like a hard job :lol: .

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Yeah these bikes are so simple and so much fun. Hit up Callum for some shinko 80/90 17. They fit great and handle well and they look good too. about 65 each . Sportier tread pattern too

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I've got a few parts on the way, so have been having a play while I wait. 

Pulled the guards off to give them a paint. I'm not sure whether I want to run it with or without guards yet... 

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Painted the guards black for now as they were covered in flaky chrome. Gave them a quick skim and a dab of paint. I think I prefer black guards over chrome anyway. 

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I was thinking about buying one of these... But my bank account disagreed. Luckily someone has posted measurements online:

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So with my powers of deduction and cardboard cutting skills I've managed a rough prototype: 

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I've only got 1mm panel steel in stock, which is probably a bit thick, but I'll give it a crack. Wish me luck! 

 

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