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Go Wisp!

Mark Daniels

Since its launch, the infamous Raleigh Wisp has long been tainted with a reputation for sedate performance.  However, this serious and intensive study would seek to show in part that Raleigh sought to address this problem that blighted its first models.

The earliest Wisp seems to appear in the Raleigh Sales Brochure, with a D-registration (1966) while most machines reached the general public between 1967 (E-reg) to 1969 (G-reg.).  Along with the launch, the national dealer network was issued a ring bound Raleigh Industries Service Data Manual, examination of which for the rear wheel (SL12) and Technical Data (WM5) lists the installation of a 44t rear sprocket paired to a 12t front.  This gave the highest standard geared combination available from Motobécane at the time of 13.8:1 (exactly the same as comparable RM4 & RM6 models), but the tiny 12" wheels (16" diameter) could hardly convert this to the same drive ratio as the 19" (23" diameter) Runabout wheels (50" circumference as opposed to 72").  This 44t sprocket is clearly pictured on the brochure illustration models and goes some way to explain the under-geared 25mph maximum of early machines, which must have screamed their little hearts out!  Resultant complaints of this stunted top speed, and the associated mechanical problems with the constant over-revving, prompted the rapid creation of a unique 36t rear sprocket made especially for the Wisp.  This can be seen on most of the later machines and gives a more suitable 11.3:1 ratio in combination with the same 12t front sprocket.

Further to the gearing situation is the specified engine power output, which is given in the Technical Data as only 1.4bhp while most basic Motobécane 'split fin' motors produced from 1963 are rated at 1.7bhp, despite both types being fitted with the same AR10 carburettor.  Made solely on the theory of keeping the float chamber level, the special Wisp inlet manifold with its increased tilt angle to compensate the more inclined engine installation, is only bored to 8.6mm, though this barely accounts for the 18% de-tune!  The principled intentions appeared unnecessary since in tests the carb does seem to function satisfactorily with a slight downdraft, so fitting a standard 12mm Moby inlet could help the breathing (or just open out the standard manifold).

Trying to find further explanations, it could be necessary to look further back to earlier 'continuous fin' Motobécane motors as fitted to RM4s.  These machines also produced only 1.4bhp, also with the AR10 carb, and were superseded in 1963 by the 'split fin' with its 1.7bhp output.  So what are the differences?  Comparison of the barrel porting arrangements reveal the same 18mm × 6mm transfers, though the 20mm wide exhaust port is only 7mm high on the 'continuous fin' compared to 9mm high on the later 'split fin'.  It seems possible that carrying over the earlier porting arrangement in the casting could have restricted the Wisp's 'split fin' barrels.  [Note: all types of Raleigh licensed engines were identified with an R prefix to the serial number on the cylinder barrels.]  Another notable difference occurring around the mid-60s was an increase in compression ratio of the 'round fin' cylinder head from 6.5 to 7.5:1.  Having identical external appearances, this only becomes discernible inside the combustion chamber as the earlier lower ratio features a full natural hemisphere blending to the gasket face, while the 7.5 shows a reduced hemisphere giving a small step to the gasket face with a recessed plug thread and decompressor valve.  The difference in volumetric capacities of 6.7 to 7.7cc is quite subtle and to the layman may only be discernible by the comparison of various heads.

Over the years, many Wisps may have experienced engine or component changes to confuse the original specifications and result in some of the various performance differences seen between machines today.  Raleigh's original intention to de-tune the Wisp motor may have been attributed as a discretionary reaction to the machines 'twitchy' handling due to the combination of tiny wheels, suspensionless construction and high centre of gravity from the rider perched on top of such a light machine.  More likely though, it was to try to compensate over-revving with the low drive ratio on the earlier models, later machines probably used the standard 1.7bhp motor once the drive ratio was improved.  Rating to 1.7bhp specification with 36t gearing should hold little to concern the average Wisp rider used to the nervous handling, but the next chapter promises to take the reader into uncharted territory and is not for the nervous or faint hearted!  Chapter 2, "More Go Wisp", offers practical tuning up to twice the originally specified power output - 2.7bhp!  Blueprint those braking systems and journey into the secret world of the 'Suffolk Racers' as development over three decades results in the first working prototype of the 'Raleigh Wasp', where no Wisp has buzzed before!

First published, June 2001

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