Honda c90 z2 – introduction

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Honda’s Super Cub step-through motorbike is the most successful motor vehicle ever built and a staggering number – over 100 million – have been sold.

my Honda C90 z2 (1978)

Having sold my modern Vespa GTS300 I was on the look out for an inexpensive second hand run-about. Initially I had high hopes I might find one of the great 1970s classics: a Suzuki GT 250 2-stroke. Sadly it turns out I am not the first nostalgic old duffer to look forward to reliving his youth on a vintage Suzuki and legions of fellow oldies have already snapped up most of the survivors. Kawasaki and Yamaha also made cracking bikes of this displacement but It is now hard to find unrestored 250s of any make from this era, and the few that remain tend to command a high price (and are increasing in value rapidly).

A new plan was needed. Despite my youthful interest in nippy 250s I have always had a fondness for scooters and before long I settled on the idea of getting an old Honda C90. The C90 is an undisputed classic and, unlike most other vintage bikes, low mileage examples can still be found for around a £1000. Given the massive numbers sold, I blithely assumed good used ones would be two-a-penny but it seems many of them have been ridden into the ground or have rusted to pieces and – where they have survived – there is a small but enthusiastic group of c90 fans ready to snap them up.

After much patient hunting I was lucky enough to find a low mileage 1978 C90 being sold a few miles from where I live.

Honda, started making their first 50cc step through “super cub” bike in the late 1950s but it was not until 1964 when they introduced the wildly popular “90” (actually 87cc) model, the CM90.

Advert for the CM90 when launched in the US market in 1966

the original CM90 used a pushrod OHV engine that was based on the C200 Benly 90 but a couple of years later Honda released an all-new OHC engine and called the new model the CM91. Honda were so confident in the new engine that they offered a 2 year warranty, a guarantee that was unprecedented at the time. Their confidence was not misplaced and the engine design remained in production for over 35 years1)the last bike to use the engine – albeit with a more modern charging system – appears to be the MD90 which was sold as a mail delivery bike in Japan and was made until the early 2000s. My 1978 bike is one of the C90-Z models produced between 1977 and 1983. Honda called the initial models ‘z2’ and the later models (which came with a new gear change pattern) the ‘ZZ’.

The Z2 and ZZ bikes get a bit of a bad press, owing mainly to their electrics, which were based on a 6v battery ignition design that Honda had first started using in the 1950s. The bikes do not come with a regulator to control the amount of charge going to the battery, instead the design attempts to balance the alternator output so that it is producing enough power to run the electrics with just enough additional current to keep the battery topped up. To this end the alternator is organised with three pairs of coils – the first pair are generating current whenever the engine is running, but the other two only come on once the lights are turned on (the extra power from these coils being needed to run the lights).

There is nothing really wrong with the approach, indeed Honda must have sold millions of bikes just like this in the 60s, however, maintenance issues can cause unfortunate running problems. For instance corrosion in the wiring connections can create resistance in the charging circuit that prevents the battery from charging reliably and – if the battery is not fully charged – then the ignition is effected and this can cause the bike to run badly or make it hard to start.

That said, they still seem to have been pretty popular (Honda sold around 28,000 C90-Zs) and plenty of them seem to have survived in the UK.

My one did run for a bit during the return journey after I acquired it, but conked out after about half a mile on the way home so I pushed it the remainder of the way (6 miles!). Not an auspicious start, but I had already been warned that it had been stored unused for the best part of a year and it was thus likely the fuel had gone bad (this problem is apparently far more common with modern fuel containing ethanol, and any lengthy period of storage can gum up the carburettor).

There are lots of instructions on how to dismantle and clean a carburettor on the web, so I did as instructed and also cleaned out the fuel tank and charged the battery. Much to my surprise it ran! An oil change and a bit of work on the points, brakes followed and before long it was running reasonably well.

Apart from very basic maintenance tasks on cars and bikes, I have never done any automotive mechanical work and I am basically clueless on how bikes actually work, so this was exciting stuff! Emboldened by my early success, I decided to attempt a complete restoration. Let’s see how it goes!

References

1 the last bike to use the engine – albeit with a more modern charging system – appears to be the MD90 which was sold as a mail delivery bike in Japan and was made until the early 2000s

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