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For sale by auction at the Haynes Museum, Sparkford on 30th June 2021; What is believed to be the World's quickest accelerating four stroke 125. The last time the UK National 1/4 mile Record was set by a 4 stroke was in 1964, by Jack Terry aboard one of the legendary and now priceless DOHC, 8 valve Honda CR93 limited production race bikes at 16.18. The motorcycle below, based on a 1978 CB125T has achieved an astonishing best of 15.61 @ 83mph. Producing slightly more power than a standard CR93, but approximately 47kg lighter it has frequently run 1.8 second 60' times,on one occasion slightly embarrassing the UK National 9.50 bike champion for a couple of seconds! Below are photos of some of the extensive modifications made and a full description plus links to a number of videos.

The bike comes with a number of spares including a complete modified cylinder head with custom made inlet manifolds along with suitable sprocket for use at track days and demonstrations. Ready to run with clean oil and charged battery, just add Shell VP90 petrol and go!

 
         
  Modifying exhaust ports of Honda 125cc racing motorcycle   Custom made titanium collet retainers for Honda 125cc raing motorcycle  
 

Modifying the exhaust ports to reduce diameter

  Titanium valve collets allow 14,000rpm  
  Custom inlet manifolds made for World's quickest 4 stroke 125cc motorcycle   Custom throttle cable bracket for Honda CB125 racing motorcycle  
  Custom shorter inlet manifolds   Custom throttle cable bracket  
  custom ignition mounting and sprocket cover   Modified Dynatek CB750 ignition for Honda CB125 racing motorcycle  
  CBR250RR carburettors, custom ignition & sprocket covers, hydroformed exhaust, custom catch tank, titanium swinging arm bolt and nut, dummy sump containing total loss ignition battery.   Modifying Honda CB750 Dyna ignition  
  Custom top yoke for Honda CB125   Custom bottom yoke for Honda CB125  
  Custom top yoke, stainless steel forks plugs etc.   Custom bottom yoke  
  Modifying inlet ports of World's quickest 4 stroke 125cc racing motorcycle   Hydroformed exhaust custom made for Honda CB125 racing motorcycle  
  Modification to inlet ports   Hydroformed exhausts: weight of total system 2.2kg!  
  Serdi valve seats fitted to Honda CB125   Custom rear brake lever for Honda CB125  
  Serdi valve seat installation   Custom aluminium rear brake lever + aluminium cap screw  
  Custom chain adjusters for Honda CB125   Custom ignition cover made for Honda CB125  
  Custom aluminium chain adjusters   Custom ignition cover and shorter auto advance stub  
  Titanium cam cover bolts custom made for Honda CB125   Titanium rear brake cam custom made for Honda CB125  
  Titanium camcover bolts   Titanium rear brake cam  
  World's quickest 4 stroke 125 on show at the Bristol Classic Bike Show   Honda CB125 racing motorcycle on Brooklands Test Hill 2014  
  Chosen for NSA stand at Bristol Classic Bike Show 2013   Screaming up Test Hill at the Brooklands Museum 2014  
         
 

First run in 2008 and subsequently continually developed for nearly 9 years including regular dyno testing by UK drag race legend Tim Blakemore. Best time & speed: 15.61 @ 83mph, highest top speed in 1/4mile from standing start 84.4mph.

Built expressly for ¼ mile sprinting at National Sprint Association events, nevertheless I styled the bike along the lines of the 1966 Honda RC116 50cc twin. Flangeless rims were used as they are a little lighter. Basis of the engine is a 1978 Honda CB125T1 for which Honda claimed 16.5hp, however they never exceeded 13hp on the dyno. This one started with 12.3hp and was slowly raised by skimming the head, porting and fitting the CBR250RR carburettors. The biggest gain came from major surgery to the exhaust ports to reduce their diameter, this alone gave a further 2hp. A misfire at 13,000rpm plus was cured by making titanium collet retainers allowing the engine to continue to a maximum hp at 14,000. The bike is currently geared to peak at 14,000 rpm in top gear approximately 50 metres before the ¼ mile mark. Initial acceleration is nothing short of astonishing; my wife having achieved 60' times of 1.8 seconds on a number of occasions, quicker than our Honda CBR1100RR Blackbird drag racer!

Sharon's 100% committed riding style and accompanying howl from the exhausts led her to being known as 'Hooligan' by fellow racers. Bike and rider caused a sensation at the 2014 Brooklands Museum Motorcycle Day. Urged on by the crowd she got a little carried away and like many other top sprinters came to grief after leaping the top of the hill. Bike and rider suffered some damage but a few months later were back in action running quicker than ever. The screen is still cracked as a result of this off and the machine has the patina of a bike that has been raced for 9 years.

Chassis:

1978 Honda CB125T with cut down headstock tube. Centre pressed steel section removed and replace with large diameter tube. Frame cut off behind rear shock mounts. Custom footrest and fairing mountings welded on. Custom made rear set footrests and controls in aluminium and stainless steel. Custom titanium swinging arm spindle and nut.
Rebuilt standard rear shock absorbers with new parts in aluminium and titanium plus custom titanium nuts.

Forks:

1978 Honda CB125T, shortened re-chromed stanchions, shortened springs, modified sliders. Custom stainless steel spring retaining caps. Modified Derbi Senda 50 brake caliper on custom made bracket. Custom aluminium lower yoke with shortened steering stem. Custom aluminium top yoke incorporating ignition switch mount, aluminium crown nut. Custom billet aluminium clip on handlebars with modified Derbi Senda 50 master cylinder and custom brake lever. Modified junior MX clutch lever assembly with titanium pivot bolt. Active super quick action push/pull throttle.

Front Wheel:

1978 Honda CB125T hub in 18" flangeless aluminium rim with stainless steel spokes adapted to take CB125TDC disc. This has been reduced in thickness and drilled. Custom stainless steel spindle and nut with titanium spacers. Standard mudguard with steel brace removed on custom mounting brackets.

Rear Wheel:

1978 Honda CB125T hub in 18" flangeless aluminium rim with stainless steel spokes. Aluminium sprocket with titanium retaining studs and nuts. Custom made titanium brake cam and spindle, aluminium brake lever and aluminium torque rod. Custom stainless steel spindle and nut, titanium spacers. All custom made brake rod and parts in stainless steel and aluminium.

Bodywork:

Custom made seat in mild steel. Extensively modified Honda MT125R race fairing.

Engine:

1978 Honda CB125T, modified standard pistons, valves and advanced camshaft. Custom titanium collet retainers which allow 14,000rpm power peak. Skimmed and heavily modified cylinder head porting with major surgery to exhaust ports. Valve seats fitted by Serco and valves machined to match. Compression ratio unknown (a lot!) Cylinder head and barrel fins have been re profiled and all anti ring webs removed to replicate 1960's Honda GP engines. Custom titanium cam cover bolts. Crankcases have large bore breather and internal passages. Recent new heavy duty clutch plates and springs.
Alternator and kickstart mechanism removed. Custom ignition cover and auto advance unit mounting substantially reducing engine width. Custom sprocket cover/gear change shaft support.
Engine mounting bolts and nuts custom made titanium. Custom oil catch tank in aluminium.

Fuel System:

Custom steel fuel tank. Extensively modified outer carburettors from 4 cylinder Honda CB250RR mounted on custom inlet manifolds. Inline foam fuel filter. Custom made cable mounting bracket and choke control.

Ignition System:

Dynatek Honda CB750 Dyna S pickups with modified backplate, Dynatek coils running total loss from 12V battery in the aluminium dummy sump.

Exhaust System:

Custom made front pipes and custom made hydro formed open megaphones. Custom hand formed aluminium heat shields. Custom aluminium exhaust pipe collets and clamps. Total weight of exhaust system 2.2kg!

Maximum power output recorded at rear wheel 17.4 @ 14,000rpm, however retarding the ignition incrementally reduced this to 16.9hp but gave a substantial on-track performance boost. Total weight ready to race 80kg, 47kg lighter than a standard CR93!

The bike comes with a spare head fitted with custom manifolds together with other spares. There is substantial scope to improve performance as the bike still uses a standard cam which gives a smooth power curve from tick over. An aluminium tank and seat would reduce weight even more. This is an ideal machine to use at classic racing demos where noise restrictions are not enforced.

 
 

YouTube video of 14000rpm dyno run

YouTube video of 15.65 run against CB400N

 

YouTube Video of run against ClubChampion's RD350YPVS

YouTube video first ever run up Brooklands Test Hill, it got much quiker as the day went on!