Topic: Well, now it's XS650s.....

[zoo mob]

Picked up a '75 XS650b today, decent shape, starts right up, idles well, smokes from one cylinder, has an ugly fairing and sissybar, one float sticks, and is shakes more than it seems like it should. Runs pretty damn good, looks ok, the paint is decent at best. Came with a '73 parts bike and an extra motor. The two extra motors supposedly are "high compression motors", not real clear what this means or its implications. I'll post some pics post detailing and silly part removal. Also, any ideas on one smoking cylinder? The guy I got it from thought it needed valve seals, anyone done this?

 

[Bodain]

XS650 yamaha twins. You can ride those without ever putting it in gear. I've heard stories...... Start it up in the driveway and just let it idle. The vibration is so bad the bike will slowly move out into the street on it's own.  That shake is par for those!

[BeSeeingYou]

The 75 looks really nice.  Other than the obvious the only thing not stock is the bars and master cylinder.   Looks like the bars are from a Special and a rebuild kit is not available for the MC of the early bikes so that is a common fix. The other engines are probably just standard and not high compression engines.  Is it the compression release that gives this impression?  It was standard on the 72/73 to give a little help to the electric start.  In external appearance the engines are the same but there are some internal differences.  The  early engines up to 73 were called 256 engines and the later 447.  This may not be 100% correct but the connecting rods, crankshaft, cam and tensioner, and pistons are different.  Even so there is some interchangeability but it is not 100%.  I think the 256 pistons, rods, and tensioner are not compatible with the 447 engine.  If you plan on doing anything with those 256 engines a little research would be in order and some parts are difficult to obtain.  You will notice the frames are also different with the 74 and up being better.  The vibration is just the nature of the beast with the 360 degree crank and growing up with one of these it never seemed excessive but is is nowhere near as smooth as a 4 cylinder.  Have not done any head work on mine but the seal seems like a likely suspect.  These are very robust engines and there are no premature wear issues with valve guides or rings, the other likely suspects.  How many miles on the 75?

[OakBehringer]

Valve stem seal, rings... If it's a stem seal it will smoke a lot worse if it's been sitting for a while. The XS650 is an awesome bike. Always wanted one.

[JAG]

Ive heard about getting these things rephased ( correct term ) to allow for smoother ride??.....

[BeSeeingYou]

Ive heard about getting these things rephased ( correct term ) to allow for smoother ride??.....

You can buy a rephased engine or the parts to DIY but it is fairly expensive.  Does make a big difference though.

[mrblasty]

If you start parting the parts bike give me a heads up.

[bucky katt]

the pipe on the parts bike is pretty sweet looking. one day i'd like to do an xs650 short chopper, stock rake, extend the rear section about 6 inches or so and a stock width rear wheel as well.