Mismatched carbs on '83 XJ900

You may have seen my other thread on some questionable wiring under the seat on my recently acquired XJ900 Seca. That was the easy fix. Yay.

This next one though, I'm pretty sure is the reason the PO was willing to part with it so cheap.

I pulled the carbs out to see if I could figure out why it wasn't running right, expecting to see the usual gummed up jets. To my surprise, they didn't look too bad. In fact, it looked like the pilot jets were fairly new. This kind of made sense because I also found a plastic bag stuffed in the tool holder that had some scraps of bowl gasket and what looked like the remains of a pilot jet jammed on the end of an ez-out. Apparently, somebody buggered one up and had to use an extractor.

But I noticed something else too...one of the float bowls was wrong. It was a different style than the rest and the drain screw pointed the wrong way. I assumed somebody had broken the bowl and replaced it, so I continued the investigation.

I started pulling the slides. They didn't look bad either. Diaphragms are good. A little varnish on the needle, but generally not bad. After taking out the needle, I dropped the slide of the #1 carb back in to check the movement...WTF? It wobbled all around, and you could see daylight all around it. No way it was worn that much. So, I dropped the sane slide in #2 - and it fit perfect. How the heck can the bore on #1 be too big?

Then it hit me...that's the one with the different bowl! My guess is when whoever buggered up the pilot ended up doing some irreparable damage to the carb trying to get it out, so they replaced it. Problem is, they replaced it with the wrong one! It's a BS36 instead of a BS35! You can see that the bore at the intake is larger, and measures 36mm vs 35 on the rest. That in itself is a problem, but then they also put the slide out of the 35 in it, so it was essentially a size 1000 air jet! No wonder it wouldn't run!

So now I am in the unfortunate position of needing a new carb. Anybody got one? Are they all interchangeable in the rack, or does it have to be a #1 (clutch side) specific one?

The one on the left is the style I need. Right is the one off the 36 and also points the wrong way. Note the "correct" ones are all stamped D on the post (hard to see in this shot). The 36 has an A stamped on it.


You can see the difference in the bores. 36 on left, 35 on right.


So disappointing. I thought I might actually get it running this weekend. ☹

 

Update: I found a pair of 35mm Mikuni's on ebay for only $35. They look identical except for one thing: There are 4 holes on the airbox side instead of 2. I don't know if that matters. Certainly, I'd rather have an exact match, but these have got to be closer than the 36. I figured for $35 it's worth a shot. Who knows when I might come across anything else.

Ebay carbs:

Original carb

 

You have to work out what those vents are - it may be you can block them up? Also you need to check the throttle butterfly angle when closed is the same, and the progresion holes are identical.

 

@hogfiddles you should probably chime in on this one. If there is anyone who knows carbs AND 900s it’s most likely @hogfiddles

 

Chacal suggested he may have one. Talking to him to get some details.

 

There's a lot of different bikes that used Mikuni carbs, even of the same "series", and each one comes with a lot of different characteristics...........