Scootering, number 97, October 1993 - MB Developments sprinter (feat Tango Man picture)
The Tango Man; once banned for slapping peoples ears he took up scooter sprinting and bought a fetching wig.
A standard GP 200 Lambretta is going to be making around 10 hp at the rear wheel. No fun. Ray Kemp and Terry Sheppard's TS1 225 kit is going to be making roughly double that at 20 hp or more. Much better. The top racing scooters and sprinters add another 50 % improvement to that and are getting about 30 hp or so at the rear wheel. So where does Marc Broadhurst find 40 hp at the rear wheel from? - a staggering 400%
improvement on an original Lambretta engine. Now we are getting silly. Motorcycle tuners consider it good going to get a 20% power increase on a modern machine because the factory has done most of the tuning before them, but quadrupling the power output without nitrous oxide, supercharging or turbos is just unheard of.
As you see it here, it is in it's prototype stage and was only raced like this for two runs at the N.S.R.A. Fun in the Rain Weekend at Avon Park. After our photo session it was stripped and will be extensively re-worked before it's second outing at Manby. Despite recording the readings of 40 hp at Allgear in Coventry, Marc's confidence that he would break the scooter record on its first meeting proved to be a triumph of optimism over realism. Nevertheless, for a first couple of runs 14.5 seconds at 92 mph and 13.9 seconds at 95 mph are not bad results.
These runs highlighted lots of problems with the original frame and engine set up. Firstly and most importantly the gearing was way too low, running off the peak of the powerband by 85 mph. This was compounded by problems of clutch slip and wheel spin. The clutch slip was despite a 6-plate 6-spring clutch. For a cure, Marc is going to try an 11-spring clutch. Wheelspin was due to the engine mount and riding positions.
First exhaust mounting on the frame worked okay, but the other under the mag housing shook it senseless and made the hitachi ignition a little upset
The frame has been raked at the front and the engine moved back from the frame on a variable 3-point mounting system. Marc picked the forward sitting riding position to take weight off his wrists and avoid missed gearchanges but unfortunately it also took too much weight off the rear wheel which caused it to spin under power, especially with a brand new tyre.
Another problem was the exhaust which was mounted to the mag housing. As the engine was revved the exhaust actually shook the housing loose on its studs and caused it to move along with the stator plate, affecting the timing. Back to the old drawing board.
Lastly, and potentially more horrifying, was the fact that the engine mount on the left side of the engine started to crack, leaking air and making racing at 90 mph+ interesting.
Humungous reedvalve feeds in straight under the barrel spigot leaving the room where the old barrel reedvalve was to be filled with more transfer ports. Look at the curve in that exhaust.........sexy.
The engine is basically Group 6 specification apart from the crankcase reedvalve system which wouldn't fit in a frame with standard engine mounts. The barrel was once a TS1 but it now sports six transfer ports with the extra two taking up the space where the old inlet port used to be. As well as a huge exhaust port, two extra auxilliary exhaust ports situated above the main transfers feed (round the outside of the studs) into the main exhaust as well, and the whole lot has been water-cooled and fitted with one of Marks off-the-shelf water cooled heads. Crankshaft is a one-off machined from billet and nitrided 64mm stroke item fitted with a TZ Yamaha big end bearing and a Rotax con rod, Carb is a 39mm flatslide Dellorto and the exhaust is a one-off blown to suit this engine. Ignition is Hitachi auto advance/retard and gearing was originally a Special gearbox with SX200 1 st, 2nd and 3rd gear ratios mated to Li 150 4th but when it is rebuilt Marc will be following Trevor Harrison's move to GT200 gearing.
It's a mean, lean, white and peppermint green racing machine. Doesn't sound the same, does it?
On the frame the fuel tank is Honda C90, radiator is Kawasaki AR 125 (to be changed to DT 125) and water-pump is Mini Whale.
By the time you read this the bodywork and riding position will have been considerably altered and hopefully a dustbin fairing fitted similar to that on Richard Baker's Frightened Chicken. Also the frame has been lowered and lightened with the fitting of Honda lead forks and front wheel.
Hopefully by next issue we will have some more results. Things are really hotting up now for scooter sprinting.
STICKY.
Go back to the magazine archive index
www.mbdevelopments.co.uk