Over the past decade Honda has whittled out some amazingly successful motorcycles. Three have been quite conventional in design—Honda's 350 twin, 90cc horizontal single and the 125cc vertical single. These sales classics have done nothing very well except sell in phenomenal numbers. Honda continues to roll ageless four-strokes off the assembly line at the rate of one every 20 seconds. When combined, Honda's trio of sales leaders has placed a total of 1.5 million motorcycles in American garages since 1959. Of the trio, the 125cc vertical single is the most recent. As originally introduced five years ago, the SL125 was an inexpensive street bike with boring performance and incredible reliability. And these qualities are strong in the new XL 125.
Understanding what the XL-125 does and doesn't do well will save interested buyers future disappointments. Honda's XL-series machines encompass their four-stroke single trail and enduro type bikes. The XL 125 falls short of delivering off-road performance like the Penton, Can Am or even the Kawasaki KS125. The 11.14 horsepower engine just can't pull the XL around with gusto. On the other hand, the XL 125 offers low operating costs, dependability, quietness and cleanliness—things that more spirited two-strokes don't have. And the XL is the only four-stroke in the vast field of 21 different 125cc trail and enduro bikes.
If you don't like two-strokes, mixing oil and gas, wet fouling spark plugs, seizing pistons and other smokey side-effects of the ring-dings, then the Honda XL is your only choice.
By two-stroke standards, the XL 125 engine is a maze of complexity. The engine assembly, comprised of 232 parts, is still modern in every respect. All aluminum castings house an overhead camshaft and an all-bearing supported crankshaft and transmission. Wet sump lubrication uses the same oil bath to coat both the engine and transmission parts with 1.6 quarts of 10W 40 weight petroleum.
The trochoid oil pump drives off the crankshaft pinion gear and pushes lubricant to the crankshaft, camshaft and transmission. A centrifugal filter is mounted on the crankshaft end.
The engine remains externally identical to the original SL models. Internally the entire valve train has been modified for greater power with the same Honda dependability.
The rest of the engine is substantially unchanged. Improvements in the breathing system let the XL 125 develop approximately 10% more power than its predecessor. In order to house larger valves the seats have been moved further apart.
The exhaust valve diameter has been enlarged 1.5mm and the intake is 2.5mm bigger. Because the same valve angle has been retained, the distance from the camshaft center has increased and therefore the rocker arm length is 1.4mm greater than the SL model. Combined with increased camshaft lift, longer rocker arms push the valves further into the combustion chamber.
The exhaust valve lift is up 0.8mm and the intake is 0.3mm more. In order to decrease flow resistance, shorter valve guides have been pulled up out of the ports.
Finally, cam timing has been changed and both valves open five degrees sooner and close five degrees later for longer duration.
The major improvements in the internal breathing system are aided by a larger carburetor and more efficient muffler. The tiny 22mm Keihin was replaced with a larger 26mm venturi mixer. The exhaust system is all new; it includes a built-in spark arrestor.
When Honda re-issued the 125 as a trail bike rather than a street machine, off road accouterments took the place of road trim. The high plastic front fender and mud flap come from the MT 125 two-stroke enduro. The rear fender is also plastic. The seat and Elsinore-style steel gas tank come indirectly from the two-stroke enduro bikes. Also from the MTs are the handlebars, levers, controls, instruments and fork assembly. A final trail touch is the inclusion of the block pattern trials-type tires.
To the inexperienced eye the XL 125's decor says fra/7. In fact, however, the bike possesses better street than off-road qualities. The new chassis is more slender than the SL running gear but it's still heavy and quick-steering. The cumbersome weight, slow acceleration, skittery tires and terrible rear damper units will keep riders away from any but easy, hard-packed trails and roads. For a small bike the XL 125 is comfortable. Location of the hand controls is proper, the spring-loaded folding foot pegs are correctly placed, and the long solo saddle remains comfortably firm. Overall comfort for tall and short riders alike is superbly compromised. The 32 inch saddle height allows all but sub-5'6" riders to touch the ground easily.
A full complement of street necessities come on the XL 125. Turn signals are rigidly affixed to the headlamp ears and rear frame member. The large tail light sits high on the rear fender and places the license vertical to the ground. Instruments include an 80-mph speedometer with an enduro tripmeter and a 12,000-rpm tachometer. High beam, turn and neutral indicator lights are bright and visible. The headlight glows only when the engine is turning the six-volt AC generator.
The ignition key is located under the left side of the gas tank. As expected, cranking the engine through requires minimal effort. Cold starts require closing the choke butterfly fully and three swift kicks. The XL 125 engine is cold-blooded and the choke must be flipped open in gradual stages over a five to ten minute warm-up period. The tachometer needle climbs at an even rate to its 9500 rpm redline. There's almost no engine noise, and the exhaust rap is nothing more than a rapidly muted putt-putt-putt. Engine response in all gears is gradual; there's no surge at any point. First gear is relatively low and permits poking along comfortably on flat or slightly graded terrain.
A moderate jump to second gear taxes the engine in sand or on grades. The first-to-second span gives no trouble on street or hard-packed dirt roads. Equal spacing between second, third and fourth enables the bike to accelerate smoothly up to 45 or 50 mph. Fifth gear is set away from fourth and serves as an overdrive on asphalt. Operation of the throttle, clutch and gear lever is exceptionally smooth and easy. A soft spring in the Keihin carburetor makes throttle twisting easy and non-fatiguing. The equally soft clutch lever demands little hand pressure. The friction point arrives quickly as the lever is released but the flywheel inertia of the four-stroke single smooths out gear engagement. The transmission glides from one gear to the next. The rider must use the clutch to assure full gear engagement.
As with any small displacement bike the clutch is engaged and disengaged constantly in order to maintain speed. The big oil-bathed multi-plate unit will take great abuse with little complaint or fading. The overall gear ratio is too high for the vast majority of off-road needs. Installation of a countershaft sprocket with one less tooth would improve off road performance by allowing the engine to spin faster and remain in its power range. The XL 125 is most responsive when the tachometer needle is bobbing up and down inside the 9500 to 10,500 redline zone. The engine runs at its strongest and smoothest around ten-grand. In order to accelerate, climb or pull through sand, the engine must run past 9000 rpm constantly as the gear lever is run up and down. Honda has designed the 125cc engine to rev at the five-digit mark for long periods. Impervious to lengthy jaunts with the throttle held wide open, the XL 125 buzzes happily at ten-thousand.
Handling of the XL 125 suffers drastically from non-functioning rear damper units. The stout chassis has decent geometry with 29.5-degree head angle and over five inches of trail. The MT-type fork, with the long sliders and offset axle location, works very well in the dirt. They are as good as any forks we've seen on a small trail bike. The shock dampers, however, are typical of the Showa units used on Honda's trail bikes. They offer absolutely no restriction to spring rebound.
The absence of shock damping allows the rear of the bike to dance up-and-down like a ping-pong ball on rough water. When decelerating, the back of the bike rises quickly and overloads the front fork, thus collapsing the springs unnecessarily. In corners this causes the XL 125 to dive and plow uncomfortably. On choppy or rocky down-grades the lack of damping prevents the rear tire from getting a good purchase while braking.
As a result the back end has a desire to come around and catch the front. The sluggish engine doesn't enhance the XL 125's off-road handling. Any bike that's down on power like the XL 125 will steer poorly in the rough and out of turns.
To meet both street and dirt needs the XL 125 is fitted with Bridgestone block-pattern trials-type tires. These compromise tires meet all of the XL's street demands but give only passable traction in the dirt. The 2.75-inch wide front and 3.5-inch rear tires don't deliver the grip of bigger trials rubber or knobbies.
The absence of bead locks means high tire pressure must be used to prevent the tire and tube from slipping on the rim. Holes are provided in the rims for bead locks but they are plugged with grommets. During our final trail outing we punctured the rear inner tube—a thing of small consequence with most trail or enduro bikes. The flat tire occurred while riding briskly over a long, smooth trail at approximately 35 to 40 mph. As soon as the tire flattened the XL 125 went into a convulsive side-to-side full-lock wobble. At this time the rear tire was rolling uncontrollably over one side of the rim and then the other. An inexperienced rider almost certainly would have fallen. By the time we rode slowly back to home the tire slippage had pulled the stem and ruined the inner tube.
The wheel assemblies are derived from the SL model with its small hubs and steel rims. The brakes work well in the dirt and are adequate for moderate street speeds. Behind the carburetor is a large, washable foam air cleaner. The chassis has plenty of ground clearance. A small complement of tools will perform most minor adjustments.
Two weaknesses of the XL 125 are not acceptable by 1975 standards. Shock dampers that perform decently are certainly within Honda's reach. Shocks that dampen slightly cost little more than ones which have all the parts but don't work at all.
The absence of tire bead locks— especially on a trail bike—is sinful. Locks are cheap at the factory level and provide a crucial function for bike and rider alike. Like its predecessors, the Honda XL 125 does nothing exceptionally well. It's a small displacement, low-powered street-and-trail bike.
The XL 125 does what it does best on suburban streets and smooth, hard-packed dirt roads. On demanding trails or open highways it can't run fast enough, go straight enough or stop quick enough. The XL 125 remains inexpensive, clean, quiet, dependable, boring and slow.
Source Cycle 1975