Truenotch's 1974 Yamaha FS50 (FS1)

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11 hours ago, Truenotch said:


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



38 minutes ago, TimShadboltfan27 said:

amazing. did you do measurements yourself or are they online?


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36 minutes ago, Lord Gruntfuttock said:

Be interested to see how that pipe goes, got some software somewhere that lets you put in your engine config and it spits out the optimum tuned pipe design.
Never tried it yet. 

Yeah, I’ve had a look at design software / spreadsheets but it gets really confusing really quickly. It seems best to have the bike already running so you can work out things like approx exhaust temperature, rpm etc.

I’m pretty sure that won’t be the last chamber I build for this thing!

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I've been tempted to build one I could slide so's I could trial different length expansion chamber in road trials. Think getting back-pulse timing right is pretty important.


Black magic stuff really...

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Yay, parts day! 



Unfortunately there's a bit of work needed to make everything work. I gambled on the Polini cylinder for the Chappy being correct because of some info that I'd found on the internet, but it turns out the Polini kit has HUGE transfer ports that are far too big for my crank case. 


This leaves gaping holes around the edges of some of the ports... So I'm stuck trying to find a solution. 

You can see the difference between Polini and  standard ports here: 


My first option is to use JB weld / some type of compound to goo up the ports on the cylinder. I'd also add goo to the mating face on the crank case to get a good sealing surface. Then I can port match the cylinder from there. 

Option two.... Um.... A metal gasket or something? Not sure. 


I also need to modify the inlet to get the reed cage to fit. It needs a couple of MM taken off to fit nicely.


I'll also need to modify the chappy inlet manifold to suit. I could either add a wedge underneath to get this angle or add to the manifold with an elbow / new tube. 



Once I realised nothing was going to work today, I set about trying to make it go as a 50cc again. It was a pretty mad mission and I was trying to finish it in time for the oldschool meet tonight, but it wasn't to be. I got it going afterwards though! 

Here's my temporary headlight until I sort the wiring out: 


Took it for a hoon. It's going much better than the last test, but still not well. It splutters a lot, although I did double up on oils (premixing incase the oil pump didn't work) and the carb enclosure was open, so it was likely running lean, causing the splutter. 



I just had to ride it to make sure the next lot of effort will be worth it! And it seems like it will be... The thing is quite peppy when it decides to pull through the revs. 

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This was running pretty OK for a while until I tried to ride it to see a friend. It fired and ran once, then wouldn't start again. I reset the points and it fired up again... Once... Before deciding it didn't want to make spark anymore.

I had a decent look around everything and the points and condenser seemed acceptable and I'm pretty sure the coil is OK. Then I noticed a dodgy looking of the ignition winding and gave it a poke. It broke in half and appears to have been soldered together at some stage. 

Hoping / am pretty sure this is where the spark ran away to. You can see little soldered bits on the end of the broken wires and the last few coils of the ignition winding are loose. I think someone bodged it up years ago to make it work. 

I'll take this to an electrical barry next week to see what he can do.



I'm pretty sure this is the cause of my problems... But I'm not 100% sure. The wire looked dodgy before, but it wasn't broken. Only took a small bump to break the solder join though. I guess we'll find out if it was the main issue 

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Ignition winding rewound. Ken Cairns is great - he’s definitely getting on, but knows what’s up. This job was $30 :D . 

Missed a delivery from Yambits today... I’ll collect it tomorrow. It’s got points, clutch parts and a few other goodies to keep me busy. 

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man thats legit you got that stuff rewound


hey @Kimjon you should talk to markku about getting the wajax coils rewound. I never found anyone to do it, but could make the engine run without a battery



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