ONE IS ENOUGH
Like Frank, I am a member of the ‘one carburettor per engine is sufficient’ club, as was Burt Munroe. In the late 1970s I acquired a 1962 Triumph Thunderbird that was quite nice, but nothing special. It had been Bonnevillised by some PO, with a twin carb head, high comp pistons and big camshafts. It went well when you managed to start it, but you could never tell when it would. I reckoned it depended on how many people were watching: if you multiplied the number of observers by four, that is about the number of kicks required!
A few years ago, I stripped the motor, put in some softer cams, made a spacer and fitted it under the barrel to bring down the compression ratio, and fitted a single carb head. It transformed the bike. It made it such a lovely ride and stopped it feeling as if it was always in a hurry. More recently I fitted a unit construction nine-stud top end, (more sleepless nights for rivet counters, sorry). Now the engine does not leak or use any oil and it is so much smoother. I think the high top pistons must have upset the crank balance. Mick Cooke, member 6177
I was offered the last new Norton Commando for sale in Finland. It arrived via Saudi Arabia where a supply of Tridents and Commandos had stood in a container for ages, before being rescued by an enterprising entrepreneur. The Commandos were all rorty-torty twin-carb models as they had been exported for police use. I wrote to the makers asking if it was possible to manage with a single carb instead of the two.
Their reply included a single carb manifold for the Commando. I was told that with a single carb I’d get better starting, a reliable tickover, incredible acceleration, far better fuel economy and it would be easier to keep in tune. They pointed out that, with the rough running at tickover caused by twin carbs, the engine jerked about and raw fuel slopped down into the bores, suggesting that the engine would suffer dried bores. There was also the question of air filters.
Norton Motors said twin carbs was a ‘fashion thing.’ If the model in the showroom had only one carb then sales would suffer (or something along those lines.) That was all from the horse’s mouth! David Bullivant, member 1638
I’ve always preferred a single carb on twins, and even recall borrowing a T150 Trident fitted with a single SU – probably the smoothest Trident I’ve tried. Big beefy engines like the Commando are delicious with a single carb… Frank W