SINGLE CARB MOD

The Suzuki inlet stubs have an alloy flange moulded into them. I liberated those flanges and they got welded on to the cut and shut manifold.
Those original inlet stubs were toast, and damn near thirty quid each at the time, so it went towards the overall cost of doing a rebuild. Plus the cost of airbox rubbers and the cost of new carb internals. On two bikes.
Eff that. I refused to bend over and let myself be shafted by the Suzuki Dealer Network.

 

I do the same Dave as costs mount up quickly. It's great how you made that manifold and as they work on cars why not. I would like to make one for my own bike now. You got me thinking about this single carburettor conversion. Mabe you can post a few pictures once you make one for your XJ and advise on the best parts to use and jetting etc?

 

Well, the XJ is a relative youngster with a mere 111K miles on it, as compared to the GSs which were considerably more than that, and everything that could be vibrated to death, was, including carbs. Allied to that, if the internet had been around back in the day, I'd probably have just picked up a replacement rack or two of carbs from somewhere and just got on with that more conventional route.
What I'm saying is, the XJ might not need a single-carb made for it, but if parts dry up or become pricey, then it might get one. Even carb diaphragms are available cheaply now, unlike 25 years ago.

 

...and, to update, things are afoot.
A recent descent into bad running had me examining the carbs, and by the time I buy new rubbers (hard and broken/leaky) front and rear and new diaphragms, plus the basic cost of a minor carb refresh kit for the float chamber, it all adds up to more than I feel like paying.
A Weber is the weapon of choice, this time.
I had a close look at the room available and Yamaha having moved the alternator and starter inboard and upwards means there's no real room for an SU in there unless I have it poking out the right hand side, meaning there's going to be a torturous passage for fuel/air mix, so rough measuring up revealed just about enough room for a simple branch manifold with a downdraught Weber sitting directly on top and it can poke up between the two frame rails. Hopefully there will be enough space above it to allow a smooth flattened elbow to get air into the top of it and a cool air hose can be run to the front of the bike, with a filter cone on the intake end (details to be finalised).
I've scored a Weber 32 DIR, which is a close relative of the DGV and even though it's a production-line carb originally fitted to small Volvos, the jetting in it is changeable enough to allow proper running on a 900. I'm fairly sure it will be an improvement on the SU, as the first choke is 23mm, the second choke is 24 mm, and there are a couple of extra enrichment circuits that might (or might not) help out.
To start with, the manifold will be roughed out using 1.5" mild steel thin-wall tube going into each port stub (I'll use the original port stubs for fitting, then replace them with a set of the cheapies from China), The feed tubes will be welded onto a short section of 2" square box , mounted longitudinally, centred on the rear of the head. Cylinders 1 and 4 will be fed via slightly longer curved elbows and cyls 2 and 3 via shorter elbows.
This is to attempt in some way to give each cylinder a chance of getting an even feed, both from the primary choke and the secondary choke in turn.
It won't be be perfect, but it will work.
I expect I will drop some power, but the mere fact of having a decent choke area I might not lose too much - I foresee a loss of at least 10hp and likely 15.
However, it it gets to 115 and can sit there without being too rich or too lean, I'll be happy enough.