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by Mark Daniels

The idea with ‘Freebies’ is that you get the bikes for free, but they might cost more to fix up than they’re going to be worth…

KTM Hobby

In 1957, KTM presented its first take on the popular new moped market, in a ‘best-of-both-worlds’ interpretation the 50cc ‘Mecky’ was a single-seater scooter with pedals!  There were several makes of similar hybrid scooter/mopeds made around the later 1950s, but their lack of continuation into the 1960s probably says everything you need to know about the success of the concept.

Moving on, KTM presented its somewhat more conventional Hobby automatic moped in 1968, which was released in different versions: the original 50cc ‘Mofa 25’ version was introduced with a rigid fork and rigid frame, then joined by other model combinations with telescopic fork & rigid frame, or telescopic fork & swing arm rear suspension frame.

On the continent, a Mofa 25 could be ridden without the requirement for a driving licence, but were restricted to a top speed of 25km/h (15.6mph).  The engine was the Fichtel & Sachs type 502/1A motor with the usual Sachs 38mm bore × 42mm stroke specification for 47cc, and was simply restricted in performance by fitting a small-bore 8mm Bing carburettor.

An unrestricted automatic ‘Moped 40km/h’ (25mph) version was also offered.  This had a larger 12mm Bing carburettor and was rated at 2bhp, but was classified under different regulations and needed a driving licence.

It was a logical progression for KTM to utilise a moped engine from fellow Austrian manufacturer Puch in place of the German Sachs motor and, in 1970, a Hobby  II model was unveiled, now fitted with an automatic Maxi E50 motor rated at 2.2bhp.  This ran in production alongside the original Sachs-powered Hobby, though the Puch-powered model never made its way to Britain.

KTM’s expansion had now brought it to the point of offering a range of over 40 models and employing a workforce of 400 personnel.

Part of the KTM range

Glass’s Index records that KTM imports to the UK resumed in April 1972, with the base model Automatic Hobby rigid frame moped, then joined by the four-speed Comet Cross sports moped from May 1973, and the Comet GT four-speed sports moped from July 1973.

Listed imports of the rigid frame Hobby ceased in November 1973, when it seemingly was replaced with the De Luxe Automatic Hobby with rear suspension, however our green K-registered Hobby Automatic De  Luxe was UK registered in November 1972, so again we’re not so sure of the accuracy of the official Glass’s dating information in this case—and again it appears the De  Luxe sprung frame model had actually been introduced earlier than suggested by the ‘official’ Index (our previous red Hobby registered in July 1972).

To a casual glance the KTM might appear a fairly similar style to its fellow Austrian manufacturer’s Puch Maxi, however the Hobby is very different animal.

A (missing) continental-style, cast-aluminium lifting handle is normally attached to the front of the seat post, which would be folded out for one-handed lifting in balance.

One puzzle is why, when Sachs went to all the trouble to produce the 502/1A ‘compact’ engine, they didn’t also go for lightness and make the cylinder barrel out of lightweight alloy instead of heavyweight cast iron?  It just didn’t figure, and the bike feels quite solidly built for an automatic commuter moped, so we roll it onto the scales, and it’s 7st 4lb (46kg).

You may also wonder what might be so special about a ‘compact’ engine, and its trick is that the motor bottom-end is no bigger than the crankshaft!  The crankcase is just a round cylinder with the top-end bolted onto one end, and doesn’t have any of the additional length of conventional motors that house primary reduction drives or a gearbox.  The motor still needs a primary reduction drive, so how did Sachs get around that?  Well actually, they didn’t—it just looks like they did!  This is the moment you need to get your head around the engineering of what may be one of the most extraordinary automatic moped engines ever made: it’s got an epicyclic primary reduction planetary gear set!

After the crankshaft, in a line to the left of the motor, there’s the engagement clutch to start the engine, the centrifugal automatic clutch, then a planetary gear set, all within a thickness of just 10mm, driving out to the front sprocket, beyond which is the Bosch mag set.

It’s a fantastically engineered little motor, and all credit to Sachs for pulling off what nobody seems to have done before or since, but most of its riders would be completely oblivious of the trickery going on inside the motor—all they want is reliability and performance, and that’s where some of the shortcomings start to creep in.

The motor is built with an overhung crank, which dramatically limits its practical revs because the design becomes inherently prone to vibration as the revs increase.  The inboard engagement clutch is operated by the same cable that works the decompressor, but, if you need to replace the cable, you have to take the motor out of the frame and strip the whole thing right back to the crankcase to engage the cable in the operating arm, unless you have the impossible skills of a keyhole micro-surgeon to do it through a tiny screw plug hole in the top of the case.  For any normal human mortal it’s simply impossible!

There’s other weird stuff about the motor too, like the decompressor site in the cylinder head that Sachs left blank!  Instead they put the decompressor into the sidewall of the cylinder and vented it through a hole 20mm down from the top of the bore!  The Sachs ‘compact’ engine certainly looks futuristic with its single-sided appearance and radial finned top-end that gives the impression of a Flash Gordon spaceship, but maybe it’s best not to expect rocket-like performance from 1950s’ style sci-fi…

After comprehensively rotting away, the wheels were rebuilt with new chrome plated Takasago rims laced onto the original Sachs pressed-steel full width hubs with stainless steel spokes, and wearing new 2.00×17 tyres.  The rear hub contains a back-pedal brake operated by the pedal chain, which works a Bendix inside the hub to operate a conventional brake shoe arrangement by a gear driven cam.

Swing arm rear suspension and telescopic front forks are all greased spring units with no damping.

A 6V × 18W Bosch mag set powers the electrics with 15/15W beam/dip headlamp, 3W rear, and an electric horn, which only croaks at low revs and completely fails to work at higher revs, because it’s got a DC horn on an AC system.

A sprung parcel clip snaps down on the rear carrier but is rendered ineffective by the basket fitted on top of it.

There are several reasons why operating the Hobby feels as if it’s going to be little strange … if you rotate the pedals forward, the bike freely pedals forward just like a bicycle, without any engagement to the engine.  Then if you turn the pedals backwards it engages the back pedal brake.  Because of the hub brake type however, if you reverse the bike, the pedals don’t rotate round backwards as they would on a conventional freewheel, so Hobby is much easier to navigate backwards because reversing pedal rotation can be rather a nuisance when backing traditional cycles.

To engage the engine, there’s a large lever on the left handlebar, which is orientated so that it looks like a brake lever—but actually functions as a dual-action decompressor and starter clutch lock, in much the same manner as on a pedal Puch Maxi.  Pulling in the lever engages the motor and opens the decompressor, while turning the pedals makes it spin, then release the lever hopefully to get it to start.

Below the right-hand side panel, the petrol tap is operated by turning it back for on and down for off (like, that’s not confusing at all?)

The 12mm Bing carb has a short rod out of the top, which you push down to engage the choke shutter, and a flood button to the float chamber (just like a Puch Maxi) which you can tickle for extra enrichment when it’s really cold.  Since it’s a pleasant spring day we resist any urge to agitate the button.

You can start on the stand by kicking the pedal forward while holding the decomp, then release the lever halfway down its stroke.  Sometimes a couple of spins might get the motor to fire up, but if this fails and you get bored of trying, then pedal away, intermittently pulling in and releasing the decomp lever, and it usually starts within two or three spins.  Run for a little while before opening the throttle to clear the choke, at which point the motor settles to a regular tickover.  The exhaust sounds quiet and smooth compared to our previous red example in 2016, since this green bike is fitted with a modern chrome silencer that is appreciably more baffles than the original exhaust had.

We gingerly open the throttle to feel if the choke will clear, which it does quite readily, and with a couple of blips to clear the tubes, it feels as if the bike is ready to go!

The Sachs engine proves responsive to the throttle, delivering a strong and confident increase in revs as it steams against the single-speed automatic clutch to initiate motion, while the muffled silencer tone clears to a smooth drone as the motor comes under load.  The pedal ratio feels too low to assist the take-off, while the engine pulls doggedly through the initial phase, then slides into main drive-lock with no hesitation, and pulls onward with a strong and torquey urge as the speedo needle seems to fairly whiz round the dial.  20, 30, 40, (which should be the rated design speed), but carries on well past 50, and still going well as the needle wildly swings on round to over 60!  Maybe the 60km/h VDO speedo on this bike isn’t an instrument to be relied upon … good job we have our pacer tracking our steps.  It doesn’t take much to get this Hobby off the clock, with the needle pointing back at the rider, and even further round to the 7 o’clock position and back against the stating pin!

It’s fair to say the Sachs engine in our Hobby was revving hard during the run, but we had no idea what the score was.  Best on flat 29mph, and best on long light downhill 30mph.  The surprise was that this 502/1A motor ran clearly throughout while our previous one suffered from bouts of staccato four-stroking as exhaust gas scavenging seemed to break down as revs increased.

Our previous red Hobby’s best on flat performance achieved only 26mph, which was mostly in four-stroke firing.  Ducking into a crouch would barely make any difference since the bike was more held back by its disrupted combustion than by air resistance, and the best downhill run in a crouch paced at 29mph.

The engine on this green example was obviously running cleaner than our earlier red bike, and seems to relish the challenge of any uphill climb, as the engine digs in hard to power up any ascent.

The Sachs 502/1A engine has a contained operating rev range because of its design, and will only work within that envelope.  It really wouldn’t be sensible to try and make it do any more than it does in standard trim.

Though dull at tickover, the lights seemed pretty good once the revs got up, and Hobby only has a 6V × 15W AC headlight and 3W tail.  Both brakes displayed effective performance, however the rear seemed to need a long arc of back-pedal rotation before it would engage, which made its operation point particularly difficult to judge, and the brake could readily come in hard when it did bite, so the rider needed to be careful.

Another trap the unfamiliar rider can easily fall into is instinctively grabbing the decompressor lever in mistake for a brake, which doesn’t quite achieve the desired stopping result…

It may seem slightly unusual for a bike equipped with a decompressor to also be fitted with a cut-out button to kill the ignition (early pedal versions of the Puch Maxi had a similar arrangement).  Most machines started on a decompressor are invariably also stopped on the decompressor, but using the decomp lever on Hobby also engages the clutch, so if the bike is standing on its wheels, it clumsily lurches forward to stop in a stall (not cool).  Push the cut-out button and the engine just quietly dies out (much cooler).

If however you happen to have put the bike onto the stand while the motor is still ticking over, then pull in the decompressor lever, it doesn’t stop! The rear wheel starts spinning because the starter clutch also becomes engaged, and pulses of two-stroke smoke loudly vent from the decompressor—but the engine continues running (very silly!)  This seems to happen because the decompressor only partially decompresses, because it ports through the sidewall of the cylinder, so there’s still enough compression for the engine to continue running with the valve open.

KTM continues as a successful manufacturer of modern sports and Supermoto motor cycles, but no longer makes mopeds.

The KTM Hobby was a total wreck that came as a freebie, but what’s been the cost to fix it?  Rims, spokes, and re-lace £228; tyres, tubes, rim tapes £42; silencer £40; speedo drive £10; blast cycle parts £80; paint £27; headlamp £65; tail lens £10; decompressor £20; switch £15; piston rings £12; capacitor £8; handlebars, pedal arms, and cotter pins £22; pedals £7; grips £4; cables £60; side panels £50 = £700 and a huge amount of work!  Would it even fetch that much?

Yamaha Passola

Back in January 2017 we featured a very low mileage Yamaha Passola electric-start model and, seven years later, we have another Passola—but this time it’s the ‘other’ kick-start model.

Evolved from an earlier naked-frame, step-through Passol S50 model which was launched in Japan in 1977 (but not sold in UK), the Passola was a panelled mini-scooter derivative developed in 1978.  Yamaha released its Passola SA50M kick-start mini-scooter model in the UK in May 1980; it was powered by a fan-cooled two-stroke motor of 40mm bore × 39.2mm stroke for 49cc, 12mm carburettor with reed valve induction, and rated 2.8bhp @ 6,000rpm with max torque delivered at 4,000rpm.  Engine compression ratio for the original kick-start SA50M model was given as 6.4:1, but when the electric-start SA50ME version followed in July 1982, the compression ratio was ‘softened’ down to 6:1.  It’s likely the compression ratio reduction was necessary to give the feeble 6V electric starter a better chance of spinning the motor, but such a change would compromise the power output and seems to be reflected in a lower rating for the ‘Electric’ of 2.27bhp @ 5,500rpm.

There would be an explainable reason why the kick-start Passola models might perform a little better than the ‘Electric’.

Our kick-start Passola is a fairly early example, registered in September 1980, and finished in somewhat neutral combination of stale white and beige, so appears rather like a dated and discoloured domestic appliance.  Equipment is basic and controls are simple: the left bar set has switches for beam–dip, horn, and indicators left–off–right, then the right bar set has lights on–off (but no starter button), while brake lighting works from both levers.

A 40mph speedometer sits in the handlebar nacelle with a key ignition switch off–on, and just a single warning indicator light for oil reservoir level, which seemed a little odd as Yamaha ‘skimped’ on a high beam indicator lamp.  A steering lock is fitted into the headstock column and is operated by the same ignition key from a lock inside the front apron.  A helmet lock is fitted to the rear left of the saddle, and again works from the common ignition key.

The 6V battery can be accessed for service by tipping up the seat, so you can slide the battery cover forward without having to take off the rear carrier frame (and box), but fitting the box on the carrier does complicates the matter.  Beneath the saddle is the fuel tank with indicator gauge and the oil reservoir filler, but the original spark plug spanner kit strapped beneath the seat has long gone—though it would have been of little use if you needed to use it by the side of road, because the spark plug is completely inaccessible without several other tools to dismantle most of the back end of the bike.  It’s like a scootering version of an executive puzzle, but with no solution.

Rear suspension is by the engine pivoting to a single strut, while the front forks are short travel telescopic.  The pressed-steel fabricated wheels are booted with 2.75 × 10 tyres.

One notable aspect of the Passola is its complete lack of the in-built storage that one would more typically associate with a scooter.  These mini-scooters were primarily just a basic form of personal transport, and may only have the small rear and front carriers (if fitted), so any real carrying capacity could only be created by fitting the front wire basket or adding an after-market rear box, which is exactly how our kick-start Passola is configured … and that genuine Yamaha forward mounted basket defines exactly the ‘soft market’, girlie mini-scooter shopper this bike was targeted at.  Because you can’t lift the bike by the edge of the saddle without the seat popping up, there’s a useful raised handle-hold on the rear carrier frame.  Fine, but when you fit a box, the hand-hold becomes completely inaccessible, so you’re reduced to hauling it onto the stand by struggling to lift the box, or dragging it back by the handlebars.

Our Passola M’s 1980 dating places the model in the early years of ‘Sloped, 30mph restricted regulation, and it accordingly wears a ‘limited specification’ decal stuck to the forward frame tube; Yamaha 50s could often seem somewhat ‘indifferent’ to actual performance compliance, but will it go as well as our Electric Passola?  Or maybe even better since the kick-start version was specified with a 6.6% higher compression ratio?

Starting is as simple as you could image, just put in the key, turn the ignition clockwise and the oil light blinks to tell you the level is good to go then, with the kick-starter mounted on the transmission case, you’ll need to stand on the left side of the bike and kick with your right foot.  Just one swing, and the motor starts up first time and doesn’t seem to even need the throttle twist-grip touching.

An automatic vacuum fuel tap will enable petrol supply as the engine spins, and the automatic thermal choke mechanism disengages as the motor warms up.  Throttle response may prove a little ‘fuzzy’ in the early choke phase, so it can help to let the engine run and settle for a while before setting off.

Opening the throttle from standstill delivers a soft and smooth getaway, with mild acceleration in first gear up to a change point around 15mph (indicated), where the mechanical two-speed automatic transmission slides the shift into top, at which the motor resumes the process of building up revs again through the second ratio.  The obviously higher 8,389 mileage motor on our kickstart Passola doesn’t feel as eager as the sub-1,000 mileage motor off our previous Electric Passola; also note that the milometer  only indicates four digits and resets after 9,999, so you’re never going to be sure how many times they might have been round the clock.

Initial take-off is commonly accompanied by a nervous steering weave as the rider comes to terms with the inherent twitchiness from the small wheels, but you’ll soon get used to this as the sloshy handling continues right up its range.  A firm hand at the tiller points Passola along the course you might like it to go, but at every bump or bend the bike feels as if it’s waiting for any opportunity to dive into the roadside bushes.  The diabolical handling is not helped as the speed increases, while we silently scream along in seemingly infinite revs.

While Passola’s motor runs smoothly and quietly right up its range, comparable period Honda Express and Melody models break into irritating bouts of four-stroking at their upper revs, so in that respect the Yamaha is slightly better to ride.

Not knowing the accuracy of this speedometer, and especially considering the previous Electric Passola indicated 12% slow, the test ride was tracked by our pacer.

Generally, running on flat indicated 30–32 mph with downhill peaks up to 34, while our pacer clocked this off at 35, so the speedo on this bike was consistently indicating 1mph slow, but our kickstart-M version was notably paced performing 5mph slower than our earlier Electric Passola

Passola’s road-holding was wholly dreadful, handling like a drunk at the end of an evening, stumbling out of a bar and into the cold night air.

Brakes proved effective enough, though any firm application at speed could contribute to further instability of the bike’s road manners.

The SA50M kick-start model was UK de-listed in October 1983, while the Passola SA50ME Electric continued on listings until October 1985, so even the youngest examples are now nearly 50 years old, and all qualify for historic exemption.

If you’re wondering about the last time you saw a Passola on the road, there are a number of reasons why you may not have seen one for some while—they didn’t prove particularly durable…

The centre stand comprised a riveted assembly, but the rivets commonly worked loose, so the stand fell apart, and the bike fell over.  The plastic moulded panels were particularly brittle, and completely shattered plastic leg shields became very common.  The vacuum fuel tap with the automatic thermal choke control was a combined unit with a common diaphragm, which is fine as long as it works, but when it doesn’t … the special parts are obsolete, which can be a problem, so you have to plumb in an aftermarket vac-tap to the fuel system, since that’s always the section that fails.

The rear brake tended to receive harder use than the front (for obvious reasons), and because of the small drums, their linings wore out quickly.  Removing the rear wheel meant taking the exhaust off, but Passola’s odd engine arrangement really didn’t suit the wetter northern European climate.  Passola had its carburettor at the front of the motor, with reed-valve induction direct into the front of the crankcase, meaning its exhaust was sited at the back of the cylinder, and exited directly into the front of the rear mudguard, where the tyre threw water directly onto the hot exhaust pipe and manifold nuts.  The exhaust systems rotted like crazy, and trying to undo the rusted manifold nuts invariably sheared the studs off in the cylinder.  A cover inside the front of the rear mudguard to shield the exhaust could have made a big difference to Passola’s chances of survival, but it was all getting too late by then … the mechanical two-speed automatic transmission system was beginning to look expensive and obsolete against the simpler CVT design, which was something new and cheaper that had already come along.

Our Passola came as a freebie with a frozen engine, though that was resolved with work and no requirement for motor parts.  So total cost to fix it?  Tyre £20, brake shoes £16, tank clean £40, vac-tap £8, battery £14 = £98, + a fair bit of work and time.  The bike has been on the road and in regular use for the last year, which seems like a worthwhile result.

Next—Our main feature ‘The Ghost’ may well compromise prospects of a third feature in our next edition, but if we do find space to squeeze something in, then we might be going on ‘Safari’ with some notes from the Denny tapes.

This article appeared in the April 2024 Iceni CAM Magazine.
[Text & road test machine photographs © 2024 M  Daniels]

Making Freebies

The idea with ‘Freebies’ is that you get the bike(s) for free, but they might cost more to fix up than they’re going to be worth…

Both the bikes in this feature came from John Squirrell, and both were machines that were already long dead when he got them, then stored in a damp shed for some ten years before Mopedland workshops were ‘lucky’ enough to get the opportunity to fix them—but at least we got the bikes for our article.

We had (sort of) covered both machines in previous articles, the red KTM Hobby in Fifty Quid-2 in September 2016, and an electric-start SA50ME Passola in the New Generation article of January 2017, but our latest kick-start SA50M was actually a different model.

Theoretically the higher compression ratio SA50M kick-start version (6.4:1), should have performed better than the lower compression ratio electric-start version (6:1), though the ‘M’ was obviously higher mileage and maybe its best days were behind it.

As it worked out, the electric-start surprisingly outperformed the higher compression kick-start, which we could only put down to motor condition, since both bikes seemed to run well enough, just that the lower mileage electric-start engine felt stronger.

From a decrepit wreck with a seized engine, the Passola SA50MM recovered well: to a decrepit wreck with a running engine; though everything worked, so it was put into use and, with a little further running maintenance, it was still in use a year later.

The KTM Hobby has a unique motor in the Sachs 502/1A, which has a planetary gear set for the primary drive reduction, but this is all internal mechanical trickery, and the greater majority of riders in the 1970s who purchased these machines would have had no idea of the wonders inside their engine.

The Hobby was just a humble and basic priced moped.  The main expectations of its customers were cost and reliability; while it happened that the bike was cheap, unfortunately it didn’t prove so reliable.  The Achilles heel proved to be failure of the decompressor/clutch-lock cable, which instantly rendered the motor unable to be started, and replacement of the broken cable required the entire bottom-end of the motor stripping out to engage a replacement cable.

Surviving Hobby examples are now few and far between, so when we get a chance at another one, yes, we’re going to take it.  This green example worked out very different from our first red example in 2016.  Green’s motor ran much cleaner with no four-stroking and achieved 3mph faster on flat, while red had spluttered out at 26.

The general performance and running difference might be put down to better carburation, though both bikes were fitted with the same carb model.  Maybe red was running rich?  Possibly different float levels?

It seemed unlikely the new versus old silencers were a factor, but who knows?

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