1973-74 Yamaha TX650 & TX650A

1973 Yamaha TX650

1973 saw Yamaha introduce the TX range of motorcycles which included the TX750 and TX500. Yamaha felt a common prefix was needed for their four stroke range of motorcycles and although the 650 was not related to the TX500 and TX750 it received the same prefix. The TX650 introduced in 1973 had few changes from the XS2 although it did receive a larger, more rounded fuel tank and a new paint job. Some frame improvements were made in the 1974 TX650A to address the handling woes of the previous models and the compression lowered slightly in an effort to reduce vibration.

Yamaha TX650 Brochure

Road Test from Cycle Guide - September 1974

This year’s TX650 gets an A on its name…and a C+ on its report

Multi-cyclinder super-bikes have evolved into machines that can handle almost as well as twin cylinder bikes, even though the multis are wider, heavier and have a higher centre of gravity. Even so, heated debate still takes place all around the world as to which design, twin or multi, is the best.

All the pros and cons of multis have undoubtedly been considered by Yamaha, but they have stuck to their twin-cylinder guns.  Instead of taking a big jump into a three or four cylinder touring machine, they have elected to refine their present line of twins. Since its inception in 1970, the Yamaha TX650 twin has been battling for positive recognition. It has sold well and has been one of Yamahas most reliable models. But the original XS1 had some unusual handling quirks that have been part of the bike since the beginning. Some riders never let the 650’s wiggling and wobbling bother them but others, whose level of tolerance was much lower, confessed to never feeling quite confident aboard a 650 Yammie.

This years 650, called the TX650A, has gone through some frame and suspension changes that are major enough to qualify the chassis as being all-new. Yamaha made these changes in an effort to rid the 650 of its unusual handling traits, which, in turn, would clear up any blemishes on the bikes reputation. Since the primary advantage of a twin is supposedly better inherent handling, the TX650 would not be considered a true success until it overcame its inhibited road behavior.

Our test bike, the Yamaha TX650A, uses the same powerplant as last years TX650. The narrow, very tall engine retains its slightly over-square 75mm bore and 74mm stroke, which gives it a total displacement of 653.8cc. The compression ration has been lowered to 8.4:1

Straight-cut primary gears transmit power from the 360 degree crankshaft to the large, multi-plate wet clutch and five speed gearbox. The gear ratios are close together and evenly spaced, so no big RPM drops occur between shifts.

A single row chain drives the overhead camshaft, and dual 30.6mm Mikuni-Soles, constant velocity carburettors supply the gas mixture to the engine. A two-piece airbox mounts under the front portion of the seat and houses a pair of washable, oiled-foam elements. Another piece of foam is  placed behind each element to filter out the big pieces. An easy 90-degree turn of the wing-nut knob on either side panel gains access to the filters.

The Yamaha uses a conventional battery/coil ignition system. Dual breaker pointsmount at the left end of the overhead cam, and a massive AC generator hangs on the left end of the crank.

A panel just in front of the handlebars holds the speedometer (which reads nearly five MPH fast at 30 and 60), tachometer , ignition and idiot lights.

The 650 uses a double downtube frame that has a single, large diameter backbone. Heavy bracing and gusseting have been added to this year’s frame to give it added strength and permit less frame hexing. 

The bike has a sidestand on the left and a centrestand; it doesn’t take much effort to get it up on the centrestand, but you must lean the machine way over to the right of centre to get the sidestand down. If you have short legs, or if you’re standing on the left, the bike can easily fall over on the right side while you are trying to get the sidestand down.

The TX650A uses alloy rims at both ends, with a 3.50 x 19 Yokohama ribbed tyre up front, and a 4.00 x 18 Yokohama universal on the rear. A double-action hydraulic disc brake stops the front wheel, and a single leading shoe drum brake gives the rear wheel its stopping power. The front forks allow 4.9 inches of wheel travel and the five-way adjustable rear shocks permit 2.8 inches of rear wheel travel.

Chrome fenders, shocks, exhaust pipes, and chain guard contrasting with the matt black finish of the handlebar switches and instrument panel give th eTX650A a neat, modern appearance. The four gallon (last year was 3.7 gallon) cinnamon brown gas tank, side panels, and headlight also blend in nicely, but the frame detracts from the bikes otherwise clean overall appearance. It has gussets supporting gussets and frame tubes bracing frame tubes, all held in place by thick, heavy welds. Other than that, the machine’s workmanship is well above par, and all the pieces fit nicely together.

The TX650A has a wide range of usable power which begins just above idle and lasts to engine redline at 7,500RPM. It builds power smoothly and steadily and there is never a spot in the powerband where the engine comes on all at once. There aren’t any flat spots throughout the range either. The bike accelerates best between 4,000 and 7,500RPM; maximum horsepower is is at 7,000RPM, and the torque peaks at 6,000RPM.  The steady pull gives you the feeling the bike isn’t exceptionally fast. We were really surprised when it turned a 14.42 second quarter mile with a terminal speed of 92.9MPH. These figures are close to some of the superbikes we’ve tested.

To start the engine when it’s cold, push down on the enrichener lever on th eleft carb, turn the key on, and push the starter button. After a few seconds of cranking, the engine comes to life. Let it idle for 30 seconds or so, lift the enrichener lever, and you’re ready to take off. When the engine is warm, the procedure is the same, except you don’t need the enrichener at all. There is also a kickstart system in case of failure in the electric start system, but it takes a healthy prod to turn the engine over. Last year the TX650 had a small lever on the handlebars which was hooked to the starter motor and also operated and exhaust valve lifter (which acted like a compression release). Pulling this lever would activate the starter and lifter simultaneously. But the starter cranked the engine over so violently that it often jerked the crankshaft flywheels out of alignment. Once this happened, the already heavy engine vibrations would become heavier.

The TX650A doesn’t have the valve lifter this year, and it uses a starter motor that transmits less torque to the crankshaft so the crank stays in alignment. But it sometimes takes three or four pushes of the starter button before the starter gears engage. The spring in the Bendix starting unit is too strong and wont always allow the starter gears to mesh. The resultant clunking and whirring sounds are terrible.

The TX650A is tricky to get moving from a dead stop, so you have to aquire the knack for smooth takeoffs. The routine and be attributed to a mild lack of flywheel effect and a short clutch engagement span. There is only three-quarters of and inch of lever travel from the point where the clutch is disengaged to where it is fully engaged.

For the smoothest starts, we found that revving the engine to 1,500RPM and letting the clutch lever out very slowly was the easiest way and required a minimum amount of clutch slippage. If the engine RPM was below this point, the bike would chug and surge and sometimes stall when the clutch was engaged. If the revs were above 1,500RPM, we had to hold the clutch lever within this three-quarter inch engagement area until the bike was moving about 10 to 12 MPH.

Once you’re underway, the engine won’t let the bike run smoothly below 10MPH. It chugs and jerks, so you must continuously slip the clutch to keep the engine from stalling. This chugging is caused by and excessive amount of slop in the drive train, the constant velocity carbs, and the lack of flywheel effect.

The Mikuni carburettors aren’t as temperamental as the Keihin units on the TX50, but the bike idles erratically and often surges when the throttle is held in one position. Altough we adjusted and readjusted them, they still didn’t perform perfectly. Above 10MPH the engine works well; it never wants to chug or bog out unless the revs drop down below 1,500. There is plenty of overlap between the gear ratios, so the engine RPM doesn’t drop much between shifts. When you’re in the hefty part of the powerband, it’s easy to stay there.

The TX650A has enough power to cruise the freeways and open roads easily. There is enough reserve power in top gear to let you move easily with the flow of the traffic. For the quickest acceleration to pass slower vehicles you have to downshift once or twice to get the revs above 4,000; but you can also pass comfortably in top gear. At freeway speeds of 55MPH the engine is only turning an easy 3,700RPM in fifth gear or 4,200 in fourth.

If you like to play racer on winding roads, you don’t have to shift a lot to keep the engine above four grand. Third gear lets you run close to 80MPH without over revving the engine, and in fourth you can go over 95MPH. If you are riding into a headwind or up a steep grade, the 650 has plenty of mid-range torque available to churn out the miles without the need to downshift frequently.

Yamaha found it necessary to redesign the cylinder head cover for more efficient top-end oiling.  However, improperly designed baffles in the cover let oil seep out the breather when the engine is running; and when it’s stopped, oil that accumulates in the breather hose falls to the ground.

We liked the gear ratios and overall gearbox operation very much.  The shift lever travel is short, and the shifting was always smooth and positive.  When the bike was new, we experienced some difficulty finding neutral from first gear.  About 50 percent of the time we would miss neutral and end up in second.  But shifting from second into neutral was always a no miss proposition.  After the gearbox limbered up, this problem ceased and we never again missed a shift.  The clutch took some punishment, but it always acted like it should:  It never chattered or grabbed.

The TX650A’s gas consumption is one thing that could hinder its long-distance touring.  We obtained anywhere from 35 to 42 mpg during the test, with an overall average of 38.3 mpg.  This means the bike can go about 150 miles between fill-ups.

The frame has undergone some critical changes to prevent the wobbling that existed on previous 650 Yamahas.  First, the swingarm was lengthened an inch and beefed up for more strength and rigidity.  The frame is now heavily gusseted around the swingarm mount, steering head, and rear engine mount.  The engine has been moved forward 10mm and lowered 10mm to get the center of gravity lower and further forward.  The steering head was lengthened slightly, and the fork offset (distance between the steering shaft and the fork tubes) shortened by 13mm, making this distance the same as on the TX750.  The TX650A now also uses the same forks as the TX750.

The longer swingarm increased the wheelbase to 56.5 inches.  The 650 retains its 27 degrees of steering head angle, but the front wheel trail has been increased from 3.9 to 4.4 inches, due to the shorter fork offset.  But even with these new frame changes, the TX650A possesses a strange chassis combination that makes the overall handling really different from the street bikes we’ve previously tested.

The TX is still a 474-pound heavyweight, and it is still noticeably top heavy.  45.7 percent (217 pounds) of the weight rests on the front wheel, and 54.3 percent (257 pounds) is on the rear.

The high center of gravity adversely affects the bike’s slow-speed cornering, low-speed maneuverability, and directional stability in crosswinds.  As you go through a slow turn, the bike sits up slightly and heads toward the outside of the comer when you open the throttle.  You must make a small, quick steering correction to keep going where you were aimed.  The bike doesn’t veer off course a great deal, but enough to be annoying.

Also, as you creep along in slowly moving traffic, you must continually weave the handlebars from side to side to keep the bike upright and going straight.  Often, even this steering technique won’t work, so you must dab with your foot to keep from tipping over.

On the road, crosswinds and gusts from passing trucks make the TX tilt from side to side, often causing the bike to wander a few inches off course.  With a full tank of gas, the center of gravity is raised, and the bike wanders even further.

Yamaha stiffened the 650’s front forks and rear shocks, which successfully improved its high-speed cornering through smooth turns.  The bike never wobbled at high speed nor did it do anything unusual in these turns.  You can pick a line through a smooth corner and the machine will follow it precisely.

The footpegs and mufflers are higher this year, so we could lean the bike over much further without encountering premature grounding problems.  If you play racer and push the machine to its limits, you will drag the footpegs when rounding smooth, slightly banked turns.  Through fast, flat corners, the sidestand will drag when turning left and the muffler mounting bolt scrapes when going right.  If you’re a more casual rider, you can achieve reasonable lean angles without anything digging into the pavement. 

Both tires hold the road well, so there is never a worry about them sliding out or losing traction unexpectedly when you’re leaned over.  At the lean angles the bike is capable of reaching, there is almost a quarter inch of unused tire tread remaining.

The stiff forks and shocks are an asset for smooth cornering, but if the turn is bumpy or rutty, you must pay close attention to where the bike is going.  The suspension units on our test bike were insensitive to these small bumps and caused the machine to change direction slightly in the turns. Instead of absorbing the bumps, the suspension caused the bike to veer off course.  The change in direction isn’t violent, but you must make small, deliberate steering corrections to keep the bike going where you want it to go.

The TX650A cruises along smooth highways and open roads nicely.  You can change lanes quickly and predictably, and zip in and out of traffic with ease. 

But on rain-grooved freeways, the front end has a noticeable wiggle, and you must make a conscious effort to keep the bike going perfectly straight.  This wiggle is due in part to the ribbed front tire, which tends to follow the wavy, combed pattern on the road.  On twisty, mountain-roads, the TX650A handles best if you glide it through the turns with a gradual, smooth motion.  You can’t charge up to a corner and flick the bike over at the last moment because it responds slowly to such treatment.  If you try to manhandle it around corners, it resists.  If you use a gentle flowing motion, the bike swoops around these same corners gracefully. 

Some TX650A owners and Yamaha dealers told us that the bike’s suspension was stiff when new, which sometimes caused some of these handling peculiarities.  They claimed that the bike handled and steered quite differently once the suspension softened up slightly.  Our test bike had a stiff suspension, so we went to a local Yamaha shop and borrowed another TX650A, one with over 5000 miles on it.  We wanted to find out for sure which of the handling quirks were caused by the stiff suspension, and which were related to the high center of gravity. 

We found that the softer suspension on the borrowed bike had the ability to soak up bumps more efficiently, so cornering through rough turns was more precise and unaffected, and the need for small steering corrections didn’t exist.  And surprisingly, the cornering ground clearance was just as good with the soft suspension.  We could tilt it over just as far as our stiffly-sprung test bike, and it felt just as stable.

The other handling idiosyncrasies, the ones caused by the high center of gravity, were the same on the borrowed bike as on our test machine.  The borrowed 650 felt top-heavy around slow corners, was awkward at slow speeds, was affected by gusts of wind, and responded best to a gradual approach into a hard turn.  And since it had a ribbed front tire it too wiggled in the rain grooves.

For hour-long trips, the TX650A is comfortable; but on longer jaunts, it becomes very uncomfortable, mainly due to the thinly-padded seat.  The seat is hard and slants down at the front, so as you ride along, your body gradually moves toward the gas tank. In this area, the seat padding is thin and doesn’t offer much support.  You can feel the seat base pushing on your rear end, and after a short while you feel some saddle sores forming.  If you move back on the seat, there’s a little more padding, but still not enough to be really comfortable.  The stiffness of the suspension made the hardness of the seat even more annoying.  The inability of the forks and shocks to absorb small bumps and ripples caused the bike to bob up and down, which hammered the seat against our butts.  On our test bike this was very aggravating: but on the borrowed 650, the broken-in suspension was considerably smoother.  Solo riding on the borrowed bike was just about as smooth and comfortable as two-up riding on the test bike-and that wasn’t bad at all. And even though the suspension on our test bike is insensitive to small-and medium-size bumps, strangely enough, they absorb big jolts fairly well without transmitting much shock to your body.

The handlebar/footpeg/seat relationship is fine for people shorter than 5′ l0″, but some long-legged riders will find it a bit cramped. The handlebars are high enough and have a nice rearward rake, but you’ll find yourself sitting in a squat position, with your knees high and sharply bent. This eventually makes you uncomfortable and restless.

Engine vibration also has a negative effect on the TX650A’s comfort. You get a tingling sensation through the hard, thin handgrips, and through the rubber-covered, rubber-mounted footpegs; but the largest amount of vibration comes through the seat. 

The 650 has two rpm ranges where the vibration is most pronounced. The first occurs from 1500 to 2500 rpm; it then becomes negligible from 2500 to 3500 rpm. Then, from 3500 until redline, the vibes steadily increase as the revs get higher. The mirror is only useful in the 2500 to 3500 rpm range; at all other rpm, it’s wasted. It’s hard to tell if you’re being followed by a bus or a compact car.

One nice thing about the TX is its quietness. There is very little mechanical noise produced by the engine, and the note from the mufflers is a deep, throaty one. Our decibel testing showed that it produces only 86.3 db (A), so you won’t offend any citizens with loud, unwanted noise.

The Yamaha’s front disc brake worked perfectly and consistently during the whole test. It required only a two- or three-finger pull on the lever to bring the bike to a stop, and it never wanted to lock up the front wheel.

Although the rear brake isn’t very powerful, it does an adequate job of stopping the rear wheel. You have to press hard on the brake pedal to stop the bike, so you should never lock the rear wheel accidentally.

The brakes work nicely during panic stops. They’re progressive and stop the bike quickly and predictably without fading. The bike also doesn’t get sideways or out of shape when both brakes are full on; it stops in a straight line every time.

From 30 mph, we got the TX to a screeching halt in 37 feet 1 inch, and from 60 mph, it took 137 feet. The testers never felt apprehensive about using the full stopping power of the brakes because they worked so predictably. A beginning rider will also find the brakes reliable, consistent, and easy to use.

We were very pleased with the TX650A’s reliability. The machine spent some punishing hours at the dragstrip and on the dyno, plus many miles on the streets and highways.  Nothing broke, fell off or stopped working, and that’s what reliability is all about.  

The clanky starter and the oil leakage from the breather are problems that Yamaha is aware of.  They are currently in the process of working out factory modifications, which will soon be available at no cost to all TX650A owners.

The TX650A has a rugged, quiet engine that produces a wide band of usable power ranging from 2000 to 7500 rpm.  Once over 10 mph in first gear, it pulls steadily and strongly all the way up to top speed.  The close-ratio gearbox provides even gear spacing, and a short, positive lever throw.

The handling is unusual, with a high center of gravity that makes the bike feel top-heavy in slow turns, awkward while maneuvering at walking speeds, prone to be affected by sidewinds, and reluctant to be tossed into a hard corner too quickly.  When the TX650A is new, the forks and shocks are stiff, causing the bike to skip around and change direction while cornering on ripply or mildly choppy pavement.  After the suspension has a few thousand miles to loosen up, the 650 corners more precisely on these same turns.  And smooth, high speed turns create no problem, either when the bike is new, or after the suspension wears in. 

The seating position is fair, the seat is hard, and the ride is bumpy when the bike is new.  Again, after the suspension settles a bit, the ride is much better, but the seat still doesn’t offer much long-range comfort.  The vibration of the engine can be felt through the handgrips, the footpegs, and especially in the seat.  

The brakes are progressive and easy to use, the bike stops in a straight line, and the only reliability problems we encountered were two that the factory is aware of and in the process of rectifying.

Yamaha has done some of their homework, but not all of it.  The bike still feels very top heavy, which affects the handling quite a lot.  And if, for some reason the suspension on a new 650 should fail to soften up after a couple thousand miles or so, the owner will be in for many long miles of frequent erratic cornering and rough riding.  And although the level of vibration is lower than on previous 650s, this bike cries out for Yamaha’s Omni-phase balancing system, which could lower the vibration to a level more in line with current standards. 

The TX650A has the potential to be a true sporting bike in the tradition of the British twins that it originally copied.  It has bettered these bikes in many areas — electrics, electric starting, oil retention, reliability and ease of maintenance.  But if there’s one thing that these almost-extinct British bikes have going for them, it is near-impeccable handling, and in that respect, the Yamaha should have to stay after school for some extra lessons