Flatslide carbs on a Yamaha XS Triple - making the failpossum happy

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Flatslide carbs on a Yamaha XS Triple - making the failpossum happy

Post by der_nanno on Tue Apr 03, 2018 6:49 am

Ever wondered, why nobody fits these snowmobile carbs onto a Yamaha XS-Triple? Well, I've decided to make myself a little Easter-present and finally build (i.e. modify) those flatslide carbs, which I bought nearly seven years ago.

Now, why do you buy a set of flatslide carbs and don't install them? Simple really, they don't fit and honestly don't even remotely fit at all and after looking at them with the "trained engineer's eye", I decided that at the very most I could squeeze them together an extra three of four mm between each carb, which was nowhere near the over twenty five that were necessary. But I guess I am one heck of a stubborn b*st*rd and I have the tools in my workshop to make the parts obey my bidding...  ;D



So I started by cutting off those fuel-hose pipes only to discover that this was nice, but still nowhere near close enough. After that I put them on my drill-press and drilled through from the other side, as luckily all the carb body castings are identical they are just tapped/drilled to be either a left- or right-hand carb. I did this, because I worked out, that the only way to make them fit would be to move the fuel-inlets on the outer carbs to the outside in order to have enough room to fit an inlet to the middle carb.



So the carb-bodies were put on the mill and the cast noses milled down. Unfortunately after milling I discovered that there simply wasn't enough meat on those carb bodies, to cut an M8x1.00 thread for my banjo-bolts from a hydraulics shop, so hey, why not simply make M6 to M8x1.00 adapters on the lathe... (Yes, I know M6 banjo-bolts exist, but I live in a relatively small town in Austria and even though we have three hydraulics shops, none of them stock such bolts...)



Once that was done, it was on the almost easy part, of measure, cut and thread in order to respace the carbs and alter the throttle-shaft to make the carbs sit in their new spacing. Then tack them together with the TIG and see if we follow the golden machinist's rule: cut twice and still too short.





They do look the part, once fitted...



And sound like this, mind you this was with a bottom of the pants jetting and no sync or whatsoever.



All in all: approx 15 hrs of work with taking them apart and putting back together and a lot of work on small and finnicky stuff, which isn't shown in this post, but in more detail in the blog-post below. If you want to copy my general design, try to get 1/4" or M6 banjo bolts (depending on in which part of the world you live in) and you should get away WITHOUT a lathe. Milling down the carb bodies is unavoidable though.

Blog: http://greasygreg.blogspot.co.at/2018/04/the-xs-triple-sidecar-modifying.html

What a nice way to make the fail-possum smile...

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Re: Flatslide carbs on a Yamaha XS Triple - making the failpossum happy

Post by Monglord on Wed Apr 04, 2018 9:18 pm

Nice work, bet it sounds nice to ride behind you- always liked the sound of a triple.
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Re: Flatslide carbs on a Yamaha XS Triple - making the failpossum happy

Post by der_nanno on Sat Apr 07, 2018 10:24 am

Yep, the sound of the triple is pretty amazing... Carbs need some more tweaking to be really satisfying in performance.

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Re: Flatslide carbs on a Yamaha XS Triple - making the failpossum happy

Post by virusjohn on Sat Apr 07, 2018 8:53 pm

xs rort + flatslide chatter makes for an awesome sounding machine, good work.

How did the making the new throttle shaft go by the way?

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Re: Flatslide carbs on a Yamaha XS Triple - making the failpossum happy

Post by der_nanno on Mon Apr 09, 2018 2:28 pm

Not too bad really, made a nice tight-fitting center punch for it and then just drilled it in one go on the mill. I will (eventually) make a new shaft from stainless, but a man's gotta ride as well...

Oh and I made new spacer rails from stainless, because feature creep. (And I have a second carb, which will get the same treatment and then flogged for stupid money - I hope.)

Which basically means tomorrow or Wednesday, when I am doing some more re-jeting, I'll be making the new shaft.

Pictures (and more writeup) here: http://greasygreg.blogspot.com/2018/04/the-xs-triple-sidecar-modifying_8.html

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