So what's the difference between XJ and XS?

What;s the difference between an XJ and an XS? Just curious because to me they look almost like the same bike.

 

Yamaha was inconsistent in applying model designations. There is a wide varity of engine types within both the XJ and XS lines, and a mix of methods for driving the rear wheel as well. For the most part, the XS series preceeded the XJ series in development (though there are, you guessed it, exceptions).
The skinny is that the XS line are all triples (barring the exceptions), and the XJ line are all inline fours. The list of exceptions is almost as long as the list of the "true to definition" models, and the XJ1100 is really an XS1100 wearing different clothes (for the most part). Then there are the non-XJ models that use a mix of XJ parts.
In conclusion; Yamaha was inconsistent in applying model designations.

 

an extra cylinder or two

 

XS=extra sylinder?
I thought the xs650 was a twin... I guess that's one more than a single!

Modern equivalent... XSR 700 is a twin, XSR 900 is a triple. Therefore,

 

The XS 650 is the twin. The XS750 and XS850 are triples, and the XS400 and XS1100 are inline fours.

 

and a sx is a ktm

 

I thought xs400 was twin also?

 

You are right the XS400 was a twin, but the XJ400 came in 2 and 4 cylinder versions. Also there was the Diversion XJ400 and the earlier Seca XJ400, which is where the confusion lies.
The XJ series had been developed with the alternator behind the engine cylinders running via a chain whereas the XS bikes had the alternator running on the end of the crankshaft via a flywheel spinning inside the static windings bolted to the engine cases.

 

XS models also have kickstarters.

 

Not all the 1100's have kickstarters. My Midnight Special doesn't.

 

my xs 1100, or xj 1100 or xs11, or 1100 maxim has the kickstarter blocked off by the factory. it was made 2 of 81. I dont think there is any difference no matter what you call it.All the xj4s are alike exept the turbo I believe. I know a guy that restored several 3s,850s. I find it interesting that when yamaha came out with new 9, fz? They went back to the 40 year old idea of a triple.I know they are scary fast. I rode and owned 5 v4s in the touring and cruiser lineup. Now that engine is gone. The ujms I have always had a love for. The first cb750 is one i always wanted, till I owned 3 cb650s. Their headbolt design sucks.Down at the bottom of a tube. The xj bikes use the long studs and acorn nuts.Way better.