Yamaha Twinjet YL1 Salt Lake Racer

D

devilishdesigner

Been Around the Block
With the Ace ticking along nicely it's time to introduce the older cousin, our lovely Yamaha YL1 'Twinjet'. 100cc, 2 stroke twin. All original down to the user handbook. There is currently an intermittant short somewhere causing it to start and run on a varying number of cylinders, otherwise she is in pretty impressive condition for the age.

As she arrived:
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The little motor in all its glory
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Panniers on a 100cc seems a little optimistic
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First experiment for the day - A set of old bars, larger diameter unfortunately but brings the bar height down a little which is a good thing
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Ace seat on the Twinjet, actually fits quite well I think!
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Also tried a L2-CA tank on the old girl, can't decide if it looks better or worse than the original at present, what do you think?
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The end of a days tinkering
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Re: Yamaha Twinjet YL1 Custom

Nice old bike - the original tank looks way better (in my humble opinion) - and the solo seat would look better if it were longer and a little lower - but it's fun to play around like this, half your luck!
 
Re: Yamaha Twinjet YL1 Custom

Wow, neat bike!

IMO you could get the tank a little higher, it'd make the lines better.
 
Re: Yamaha Twinjet YL1 Custom

We got somewhat more progress made on the Yamaha's seat on New Years Eve.

First up was a test fit of a new set of bars to bring the hand grips down a little.
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The new taillight is just the right size, but took a fair bit of work to set it into the tail of the bike.
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Re: Yamaha Twinjet YL1 Custom

The moment some of you have been waiting for has come - Off with the tail!
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To keep it fully street legal we have made the remaining tail bolt-on to add a legal length mudguard.
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It took a lot of work to make the new handlebars work with the period levers, but it was worth it for the drop.
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The seat is now ready for leather, can't wait to see it trimmed
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Re: Yamaha Twinjet YL1 Custom

Took the Twinjet down to Kustom Nats yesterday and let Ryan Ford work his magic:
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More images of the event here: https://www.facebook.com/media/set/?set=a.720033064682760.1073741846.449052038447532&type=1
 
Re: Yamaha Twinjet YL1 Custom

Thanks, it is a pleasure to watch Ryan work his magic with a paintbrush. All free hand with only a centreline to guide him.

I was a bit worried after Kustom Nats, This is the first 100cc I've owned and it felt incredibly sluggish at the event. It would only kick start sometimes, very little acceleration, in fact it felt like it was starting in second!

Thankfully good news awaited back at the factory. I decided I was sick of the wobbly ignition switch so stripped it apart and found it was like new inside aside from 2 loose screws. Tightened them right up, put it back together and the YL1 fired up first kick, sounding far better, revving far easier, and a quick test ride brought big grins, the little motor now hoots along, in fact I'm pretty sure I could pull off a wheelie now despite weighing more than the bike, where before the ignition rebuild it nearly needed a running start to get moving. Can't wait to get it out somewhere that we can test it out properly now!
 
It's time to make an exciting announcement I've been waiting for confirmation about. On February 28th this year we will be taking the TwinJet SALT LAKE RACING!

We will be heading over to Lake Gairdner in South Australia to compete in the 100cc modified production gasoline category at the DLRA's Speed Week 2014. It will be great fun to take this unique old bike out to the salt and see what it is capable of.
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For this reason we have been busy making the TwinJet a LOT louder in the aim of making it a little bit quicker. After much fettling we have fitted up a wonderful pair of handmade expansion chambers based on designs by Yamaha's racing department back in the 1960's for this engine. They took a lot of work to squeeze around other components but the end result sounds amazingly and will hopefully give us a bit more power in the sweet spot.

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On the topic of racing, can anyone advise me on how to fit a kill switch to the Yamaha?

They were never fitted with one, and they have 2 separate coils (1 for each cylinder). From what I can see in a wiring diagram each coil has an independent wire coming up from the engine (a trigger I assume) and both share a common brown wire.

from what I can see in the wiring diagram below the brown wire is the power feed to everything on the bike. If I was to earth the brown wire using a kill switch I imagine that I would basically be hooking up the battery to the frame (bad thing, melty wires) is this correct?

 
A bit more work this week on the Twinjet. Exhaust all painted up, racing spec chainguard and battery bracket made up. Still having running issues but will hopefully have it sorted soon.

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Slow progress on the Twinjet. A carbie rebuild fixed the running issues, although a tune is certainly in order. I am going to have to scratch-build a kill switch this week to make it work with the Yamaha's wiring. Seat is back from the trimmer and looking good, and racing number plates are on.

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We did it! a 3000km round trip and a week on the salt but we loved every minute. The Yamaha gave us some grief, the old 6V electrics weren't up to full throttle racing anymore and a weak spark on one cylinder resulted in only acheiving 54 miles per hour, but we were still wrapped to have had the opportunity to race.

Sorry about dragging my heels with the photos. I've still got a few to upload of the bikes out on the salt, but for now here are a few from the event.

Full photo album is available at https://www.facebook.com/suuscustoms/photos_albums
Full writeup at http://suus.com.au/speed-week-2014-suus-gets-two-records/

We also put together a little video: https://www.youtube.com/watch?v=dJQTafL1l7I

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