XJ900 Seca Saga Continues...butterflies and throttle shafts

To catch up for anyone that missed my previous post where I discovered that someone had replaced the #1 carb on my newly acquired '83 XJ900 Seca with a BS36 instead of a BS35, I found a good price on a replacement but had to wait for it to arrive from Germany. As a result, the project has been on hold while I waited for it to arrive.

It finally showed up the other day, so hopeful that I might actually get this thing running today I started the process of swapping everything over. Most of the parts are the same, so that was easy...and since they had used what I assume was the original BS35 slide in the BS36 carb (that was how I noticed something was wrong), even the slide transferred over nicely.

However, what I failed to consider was the butterfly valve. The one in the 36 is actually a 36, so no way it's going into the 35. No worries I thought, I had picked up a couple super cheap BS35's for a different application and they had butterflies in them, so I could repurpose one of those.

Well, no. Despite them looking like 35's and measuring like 35's at the opening, I hadn't noticed that the bore steps down to probably 34mm where the butterfly is. Which means they are slightly smaller. Which means that even though they are stamped with the same number (135), they don't fit. The are too small and have gaps around the edge. Pretty sure that won't work any better than the 35 slide in a 36 body.

So now I need to find a butterfly.

Which also raises the question of the throttle shaft. I can take the one out of the 36 and it fits in the 35, except that the cutout where the butterfly passes through is slightly wider than the bore. (distance between red lines below)



Seems like it shouldn't be a big deal. It just means that flat area will extend into the bore for the shaft a little instead of sitting flush with the main bore. Do you think that will be a problem? It doesn't seem like that would let air by any more than when flush since the butterfly itself is what actually provides the seal.

 

The only problem I foresee is the hole placement on the shaft as compared to the ends.
If it is central you are correct but you are in uncharted waters... And waters I don't want to visit.

Hats off to you if all things play out.

 

I ended up just getting a shaft and butterfly from Len. But that uncovered another issue when we discovered that most of his stock of shafts turned out to be too narrow. Weird. Still a mystery to why. Finally found one that fit but now I am back to fighting the screws in the rest of the carbs.

Btw: I believe I tried mounting the butterfly when I was fiddling around trying to figure out why I couldn't get it in the narrow one. It mounted up and functioned no problem. Just the extra inset on the ends that I wasn't sure about. I also have one out of a 34 which could be made to work with a little machining. I think the shafts are all the same with screw placement, it's just the width of the slot and flat that change.

 

I didn't realise the original screws were peened over the first time I pulled mine apart.
That was bad on one carb. Had to drill it out of the shaft after snapping the head off.
Small file on the rest, removing the peened thread on the rear was the way to go.

 

I came up with this gizmo to help avoid damage to the body when grinding off the peened ends with a Dremel. Worked great!

https://www.xjbikes.com/forums/thre...le-shaft-butterfly-screw-removal-aide.132783/

 

Very cool!