Tech Info

A Boyer Electronic Ignition for a Tri/BSA. twin can be used on the Arrow . The ignition is timed at 2500 rpm. using a strobe when the system is at full advance ( 10 degrees ). The small amount of retard at low revs. helps with starting. A small amount of machining is required to fit the ignition rotor to the Ariel cam and to add a thicker washer to allow the cover to clear the ignition assembly. A Pazon Ignition System is being fitted to the 270 cc Leader engine, this requires no machining and will be used with a dual output coil.

Both the Leader and the Arrow have a 12 volt electrical system using a Boyer Power Box. The set up gives controlled charging and an emergency start facility in the event of a flat battery. The 12 volt system enables higher power bulbs to be used especially in the head light.

The side panels on the Leader are made from fibre glass which although not original are lighter, the off side one being made in two pieces so the top part can be taken off to adjust the carb. without having to take the kick start or gear leaver off. The lower panel has a cut out to enable the gear box oil level to be checked, it’s sealed by a rubber grommet when not in use. The near side panel has a small hatch to allow access to the carburettor ”tickler”


See June and August Chevals 2003 – for information on front brake improvements

Twin Leading Shoe brake conversion shown below.

A 26 m/m bore Mikuni carburetter is fitted to the Arrow, with an alloy extension on the rear connecting it to the rubber air cleaner link so the original air intake filter can be used. The engine ticks over more evenly with the Mikuni carburetter and starts more easily particularly when hot.

The Arrow has a flashing indicator system fitted, the electrical side is similar to the Leader, the flashers are fixed to the head light bolts at the front and to the rear number plate at the rear. Recently the mechanical flasher unit has been replaced by an electronic one, which is more robust and reliable.

Both machines have a rev counter, which on the Leader is fixed in the clock space and on the Arrow in the extended instrument panel. It was necessary to make extensive changes to both instruments to enable them to operate from the coil take off points and give a true reading. Whilst not strictly necessary they are useful in giving an indication of the engines performance and where the power surges are in the rev range.

Alloy barrel

Con-rod with needle rollers in big and little ends

Alloy Barrels – The barrels run cooler around 10-15 degrees C and lose the heat quicker after a session of up hill running or low gear work.


Extended lever for front brake

Next Project – A leader engine with 270cc capacity and 5 port alloy barrels for extra power. This is now on the road and running well.