Yamaha XS 650

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The Yamaha XS 650 was produced from 1970 into the 1980s for the worldwide motorcycle market. In the United States, the last model year was 1984.

The XS 650 is powered by an upright, parallel twin four-cycle motor firing every 360° of crank rotation.

The 1970 model was designated the XS-1. Subsequent models were XS-1B (1971), XS-2 (1972), then they changed the model designation from XS to TX. It went TX (1973), TX-A (1974), then they changed it back to XS but went on with the alphabetical suffix. XS-B (1975), XS-C(1976), XS-D(1977), XS-E (1978), XS-F (1979). 1979 was the last year of the so-called "Standards" (owner's term meaning opposite to Special) The Es and Fs also came in Special form; XS-SE (S for Special) and XS-SF. From then on it was Specials only to XS-SJ.

All wheels (chrome rim wire, aluminum rim wire, seven-spoke cast aluminum) swap on all years.

Except that:

Drum fronts on early models are on their own.
Pre '77 & post '77 fronts have different (offset) brake disks, the wheels swap but not the disks.
Drum rear wheel into rear disk frame needs the rear drum frame swingarm too.
Disk rear wheel into rear drum frame needs the rear disk frame swingarm and also needs brake master-cylinder lugs welded to the frame.

Handling differences on swapping rear wheels:-

Standard rear tire is 110/90-18. Special rear tire is 130/90-16. Because the Standard tire is narrower it corners quicker. Because the Special tire is wider it's steadier in a straight line. Overall gearing will not change as the two tires are essentially the same outside diameter.
Left-side front disk brake (omitted on North American models only) can be added by bolting another disk to the left side of the wheel (the bolt holes are there) and the left-side caliper from an SR500, XS750, XS850 or XS11 (the fork lugs are there) and adding the other brake line & a double-length banjo bolt. XS650 stock master cylinder still works. The system needs very careful bleeding, stainless steel wire braid hoses improve the feel.

Standard (large) and Special (small)gas tanks interchange but must keep their own gas caps because they are different.

Mid-'77 the front forks had a major redesign, fork tube diameter increased from 34 to 35 mm and internals were changed (although this also holds true for various years of the same tube size). The entire fork assembly (with triple tree) will swap either way but fork parts are not equivalent. Also the brake caliper changed from a 48mm dual piston cast iron design for the 34mm fork to a 40mm aluminum single piston floating caliper for the 35mm forks. The brake caliper mounting lugs on the fork sliders are of different spacing for the 34mm and 35mm forks so the calipers can't be swapped.

[edit] Troubleshooting

The XS650 has some common problems that occur due to their advancing age and some design issues. To begin with, the swingarm bushings are plastic. These wear very rapidly, and this can cause a high speed wobble and wallowing which is very dangerous. Replace these with aftermarket bronze bushings.

The XS650 can also be very hard to start on the electric starter. This is due to a combination of issues. First off, the battery ground cable is attached to a thin piece of sheet metal which is prone to rusting out. The cables themselves are also very cheap metal, and prone to corrosion. Replace the battery cables and bolt the negative cable to a motor mount or another similar solid location. Make sure all the cables and connections are corrosion-free, and use dielectric grease wherever a connection is made. Second, the XS650's coil was weak when it was new. Nearly 30 years later it's probably trash. Replace it with an aftermarket coil and wires. While you're at it, replace the condenser and adjust your points. Make very sure the condenser ground has no corrosion.

Later models come with Mikuni CV carbs. If you have a pair of these, I'm very sorry. Chances are your bike will run fine for a week, and then suddenly run terrible for no reason, stall, or have wild fluctuations in the idle. It might go very lean or very rich for no reason. There's really not much that can be done if this is the case. The carbs must be cleaned, and the pilot passages blown out with compressed air, and then EVERY SINGLE PART in the carbs should be replaced. Every o-ring, every brass jet, every needle, everything. ESPECIALLY the floats, needles, pilot screws, and needle seats. Brass parts wear imperceptably to the eye, but can have a major effect on how the bike runs. Even this may not help, though, and you may be forced to replace the carbs with a another set. Instead of going used, you can buy new direct slide carbs, which are much simpler than the CV carbs and MUCH more reliable. They can be purchased off of eBay, and come pre-jetted for the XS650.

Many XS650's have a very pronounced wobble around 80mph, and this can develop into a tank slapper if you try to accellerate through it. There is no one fix, but there are several things you can try to alleviate the problem. First, replace the plastic swingarm bushings with aftermarket bronze bushings. Replace the rear shocks with EMGO or Progressive aftermarket shocks. Replace the steering head bearings with aftermarket tapered roller bearings. Replace the worn-out fork springs with Progressive springs, and refill the forks with the proper quantity of 10wt fork oil. Make sure all tires are balanced, and some new rubber probably wouldn't hurt either. (ME880's are a great tire). Torque the steering head nut such that there is enough drag to keep the forks from flopping to either side when you jack the front wheel off the ground. Don't hold the bars with a death grip, just keep a light hand on them.

Note - the advice provided above to torque the steering head nut beyond the recommended setting in order to prevent the forks from flopping from side to side is inadvisable. Over torquing the nut will cause unecessary stress on even aftermarket tapered bearings. It is in the owner's best interest to install a steering damper instead.