YAMAHA XS650Thi s was to be Yamaha’s first four stroke twin. Introduced in 1970, the XS1 was to give rise to a fourteen year legacy of essentially the same bike, soon to be renamed the XS650. It was built to last but unfortunately not to handle. After a few years and the help of British Guru Percy Tait, the frame matched the engine and a legend was born. HISTORY Whilst researching this article, it quickly became apparent that no source (not even Yamaha’s own workshop manuals) knew exactly what had happened to the XS650 in Canada over its fourteen years. Therefore, in order to try and make everything a bit clearer, I think I should start with a list of models and relevant years.This is as accurate as I can possibly determine.

MODEL		YEAR
XS1A		1970
XS1B		1971
XS2		        1972
TX650		1973
TX650A		1974
XS650B		1975
XS650C		1976
XS650D		1977
XS650E, SE	1978
XS6502F,SF	1979
XS650SG		1980
XS650SH		1981
XS650SK		1983
XS650SL		1984
NOTES
* S suffix denotes the ‘Specials’.
* There was no model imported in 1982 (as far as I  know).
* I could be wrong.
The 1970 XS1A model kicked things off in more than one way. It didn’t have an electric start, just a kick starter. It also relied on drum brakes all round and a Mr Wobbly designed frame. 
An electric start was added on the 1972 XS2 model as a bit of an after thought. Placed directly at the lower rear of the engine it cut down the sump capacity by half a litre and proved almost impossible to remove with the engine still in the frame. Fortunately, the brakes were improved by the use of a single disc at the front. 
The XS remained basically unchanged through out its TX incarnations, the next update happening to the 1975 XS 650 B model, when the chassis was finally modified and strengthened - much to the disgust of Mr. Wobbly.
It remained much the same again up to 1978 when all models were fitted with a floating calliper at the front (replacing the original opposed piston type). This year also saw an additional model called the XS 650 S (Special), distinguishing itself with high sweeping bars, 16 inch rear wheel & disc brake, stepped seat, short exhausts, and alloy wheels front and rear. In fact the Special was to prove more popular than the standard model, which was phased out the following year.
The only other change of any significance was an electrical update in 1980. The old electromechanical regulator/rectifier was dumped in 
favour of a solid state affair and the ignition went electronic (no more contact breakers). The Specials lived on (with a missed year in 1982) until 1985 when they were finally withdrawn to make way for other designs.Thus ended a thirteen year reign of what must have been Yamaha’s most successful middleweight twin.
THE BIKE
The XS 650’s engine is ‘only a twin’. For all of you who only know the relative smoothness of a Jap four, the XS will introduce you to a world of vibration but also unique character. Been born of an age where British twins ruled the roads, the XS was not only made to look British but it also followed the same engine layout. The crankshaft was a 360 degree design (pistons up and down together) with no balancer shafts to smooth out the firing pulses. 
Strangely, Yamaha decided to combat this by rubber mounting everything except the motor, which sort of helps but does lead to a certain amount of disconcerting free play at the rubber mounted handlebars. Unlike the British bikes of the time, it did not use push rods. Opting for the new fangled overhead cam and rocker design which is still used today. However, in order to keep that all important Brit look, the oil feed to the head is supplied by a chrome tube at the front of the block, looking uncannily like a Triumph push rod tube.
The crankshaft is built up on massive roller bearings along with the camshaft, which is mounted on no less than four roller bearings. Amazing considering that most other bikes then and since opted for running the cam straight in the aluminium cylinder head. The only protection being a thin layer of oil - check out a lot of small Hondas of the era for an example of that type of expensive oil failure. 
If you ever have to do any major engine work on one of these bikes, you will quickly discover that the engine must be removed from the frame in order to access the top end. Adding a whole load of time to any top end job. Once you do get the rocker cover off, the camchain should be split in order to allow camshaft removal. However if there’s a bit of slack in the chain, removal of the tensioner allows enough play for the cam roller bearings to slide off. This in turn, gives enough room to slip out the camshaft, et voila! If you’re going in this far, you will need to put in a new head gasket. This is a bit of a weak spot and so to avoid subsequent oil leaks the head must be torqued down again at least 500 miles after the rebuild.
Oil changes should always be frequent (every 1500 miles), since the sump capacity is small, and so causes the engine to run very hot. To allow for this always use the thicker 20W50 grade oil as opposed to the more common 10W40.
Note - there are two oil drain plugs located side by side on the underneath of the sump. Also, the oil filter is both non-disposable and so should be cleaned and refitted at every oil change.
ADAPTATIONS
Due to the longevity of this bike and the few changes that occurred throughout its life, performance parts should still be available. These range from performance carbs, oil coolers, lumpy cams, electronic ignition, big bore kits, air filters, fork braces, etc, etc. The main problem these days will be tracking them down.
There is however a certain amount of modification available with existing parts. A lot of the earlier models had all the drilling's for twin front discs. This implies that a twin disc conversion would be possible. There are still a few people around who make replacement exhaust systems - check round a few different shops to  see what’s available. If you have a post ‘79 model, it may be worth getting an earlier set of carbs which were more open to tampering and tuning.
Finally, a quick and respectable chassis mod can be achieved by fitting tapered roller bearings at the steering head and bronze or Teflon type bushings at the swing arm.

BUYING
Since the XS 650 remained basically unchanged throughout its reign, the main choice factor has to be whether you like the look of the standard or the special. To recap, the standard is road/sports styling with flat bars and spoked wheels, whereas the special is more cruiser style with alloy wheels, sit up position and stepped seat. Another asset of a long production run is choice (you should be able to find a few for sale at any one time) and a good availability of used parts.
It may be worth avoiding the pre ‘75 models because of handling problems, unless you want one as a collectors item.
Finally, a few common faults to look out for before buying. Check the engine for oil leaks. It should be oil tight but may be weeping at the cylinder head (engine removal) or around the chromed oil feed pipe at the front. This could be caused by a relatively inexpensive stripped banjo bolt, or more seriously, stripped threads at the lower union - requiring a complete engine strip! When you come to start the bike, use the electric start. If it grinds loudly and then whirs freely chances are that the starter gear is badly worn. This can be fixed by buying a new gear ($40 ish) and putting in a few hours labour. This involves the removal of the RHS crankcase cover and clutch basket in order to access the offending gear, but it’s worth taking this into account when haggling over a final price. Also, try to check the battery charging rate. A lot of XS’s stop charging properly due to worn stator brushes. These fail before their wear limit is reached and have to be replaced to bring the charging back up to par. This is a relatively easy job but the brushes will set you back around $50. Don’t be too alarmed by any engine rattles, chances are that 
the fully manual camchain tensioner requires adjustment.It only takes a few minutes to adjust, but is often overlooked. However, a word of warning. Check that the tensioner isn’t all the way in as this means a new camchain is required. To do this the engine must be removed first! (mucho dosh)
Rob Harris, CMG Online (http://www.cmgonline.com ) 
YAMAHA XS650 SPECIFICATIONS
BIKE DATA
ENGINE
Type	- Air cooled, sohc, 4 valves, transverse twin.
Bore x Stroke	- 75 x 74 mm
Capacity	- 653cc.
Comp. Ratio	- 8.7:1(‘71-’72).  8.4:1(‘73-’77).  8.5:1(‘78-’79).  8.7:1(‘80-’82).
Carburation	- 2 x 38 mm Mikuni CV type (BS 38)
Lubrication	- Wet Sump.
Gearbox	- 5 Speed, Constant Mesh.
CHASSIS
Frame Type,	Steel Tube, Double Cradle.
Suspension,	Fr - Telescopic Forks.	Rr -Tubular Steel Swingarm.
Tire Size,	Fr - 3.50X19	Rr - 4.00X18	(Pre 1979)
Fr - 3.50S19	Rr - 130/90S16	(SE & 1979 Onwards)

ELECTRICAL
Ignition -	Coil and Contact Breaker (Up to ‘79).       Electronic (After ‘79)
Generator -	12 Volt, 3 Phase, Battery Excited Alternator.
Battery -	12 Volt, 12 Amp-hour (Up to ‘73).	12 V,14Ah (After ‘74).

DIMENSIONS
Model -	XS1,2,TX	XS-B,C,D,E	S Models	2F & G
Wheelbase -	1410 mm	1435 mm	1435mm		1435mm
Seat Height -	810mm		815mm		790mm		790mm
Dry Weight -	185/194 Kg	212 Kg		210Kg		205Kg

CAPACITIES
Fuel Tank -	12.5/14 litres	15 litres		11.5 litres	11.5 L
Oil Sump -	3L(XS1)/2.5 L	2.5 L/ 2.6L(D)	2.5 litres		2.5litres

PERFORMANCE
Max Speed -	110 mph		110 mph		N/A		N/A
Max Power -	53hp@		45hp@		N/A		N/A
7000 rpm	7500 rpm	
Max Torque -	40ftlb@		36ftlb@		N/A		N/A
6000 rpm	6000 rpm

SERVICE DATA
Spark Plugs	- NGK B7ES (up to ‘74),	B8ES (‘74-’75)	BP7ES (after ‘75)
Points Gap	- 0.3 ~ 0.4 mm
Ignition Timing	- 41 Deg. BTDC (full advance)
Valve Clearances:  70~73	          74 ~75	76 ~77            1978		‘79 On
Inlet 	- 0.15 mm        0.05mm        0.05mm         0.10mm           0.06mm
Exhaust	- 0.03 mm        0.10mm        0.15mm         0.15mm           0.15mm
Engine Oil	- SAE 20W 40 ~ 20W 50
TIRE PRESSURES
Solo:	Fr - 22 psi,	28 psi (Continuous high speed)	
Rr - 28 psi,	32 psi (Continuous high speed)
Dual:	Fr - 28 psi,	28 psi (Continuous high speed)	
Rr - 32 psi,	32 psi (Continuous high speed)

YAMAHA XS650 SPECIFICATIONS
BIKE DATA
ENGINE
Type	- Air cooled, sohc, 4 valves, transverse twin.
Bore x Stroke	- 75 x 74 mm
Capacity	- 653cc.
Comp. Ratio	- 8.7:1(‘71-’72).  8.4:1(‘73-’77).  8.5:1(‘78-’79).  8.7:1(‘80-’82).
Carburation	- 2 x 38 mm Mikuni CV type (BS 38)
Lubrication	- Wet Sump.
Gearbox	- 5 Speed, Constant Mesh.
CHASSIS
Frame Type,	Steel Tube, Double Cradle.
Suspension,	Fr - Telescopic Forks.	Rr -Tubular Steel Swingarm.
Tire Size,	Fr - 3.50X19	Rr - 4.00X18	(Pre 1979)
Fr - 3.50S19	Rr - 130/90S16	(SE & 1979 Onwards)
ELECTRICAL
Ignition -	Coil and Contact Breaker (Up to ‘79).       Electronic (After ‘79)
Generator -	12 Volt, 3 Phase, Battery Excited Alternator.
Battery -	12 Volt, 12 Amp-hour (Up to ‘73).	12 V,14Ah (After ‘74).
DIMENSIONS
Model -	XS1,2,TX	XS-B,C,D,E	S Models	2F & G
Wheelbase -	1410 mm	1435 mm	1435mm		1435mm
Seat Height -	810mm		815mm		790mm		790mm
Dry Weight -	185/194 Kg	212 Kg		210Kg		205Kg
CAPACITIES
Fuel Tank -	12.5/14 litres	15 litres		11.5 litres	11.5 L
Oil Sump -	3L(XS1)/2.5 L	2.5 L/ 2.6L(D)	2.5 litres		2.5litres
PERFORMANCE
Max Speed -	110 mph		110 mph		N/A		N/A
Max Power -	53hp@		45hp@		N/A		N/A
7000 rpm	7500 rpm	
Max Torque -	40ftlb@		36ftlb@		N/A		N/A
6000 rpm	6000 rpm
SERVICE DATA
Spark Plugs	- NGK B7ES (up to ‘74),	B8ES (‘74-’75)	BP7ES (after ‘75)
Points Gap	- 0.3 ~ 0.4 mm
Ignition Timing	- 41 Deg. BTDC (full advance)
Valve Clearances:  70~73	          74 ~75	76 ~77            1978		‘79 On
Inlet 	- 0.15 mm        0.05mm        0.05mm         0.10mm           0.06mm
Exhaust	- 0.03 mm        0.10mm        0.15mm         0.15mm           0.15mm
Engine Oil	- SAE 20W 40 ~ 20W 50
Tire Pressures:
Solo:	Fr - 22 psi,	28 psi (Continuous high speed)	
Rr - 28 psi,	32 psi (Continuous high speed)
Dual:	Fr - 28 psi,	28 psi (Continuous high speed)	
Rr - 32 psi,	32 psi (Continuous high speed)