The Machismo, Thunderbird and Electra draw steam from twin-valve, single-cylinder and air-cooled 346cc engines with identical 70mm x 90mm dimensions. However, the engine on the Machismo and T'bird is a heavily tweaked version of the Electra's, courtesy AVL of Austria. The obvious external change is an alloy cylinder head in place of the venerable cast-iron block, making for a healthy four-kilo weight chop.
Bullets have a long history of troublesome valve-trains, and AVL has addressed it by making valve angles less radical and re-ducing head and stem diameters. Thus, the cylinder and combustion chamber contours were reshaped for better turbulence and efficiency, and Con-stant Velocity or CV carbs installed.
The piston on the new motor — christened 'lean-burn' by Royal Enfield — features a flat top as compared to the old-fashioned domed unit and has discarded the valve recesses in its crown and the split in its skirt. The connecting rod, and the big and small-end bearings have been revised. Pushrods and rockers have been lavished attention and the gear-type lube system has an increased rate of flow for superior delivery.
Compression ratio has been raised from 6.5:1 to 8.5:1, and will instantly be felt by riders gravitating from the relaxed Electra to the Machismo or T'bird.
These two now use electronic CDI ignition, while the Electra uses a Transistor Coil Ignition system. Starting a Bullet remains a painfully heavy task, only mastered with some practice and calf-muscle building — the optional self-starter well worth investing in. An area that could do with attention is the clutch, which feels leaden and a downright chore to use.
Vibrations on the Machismo are somehow far harsher than the other two bikes; even our visiting Autocar UK columnist Colin Goodwin was convinced he wouldn't ever bear children, having enthusiastically clobbered it over many kilometres.
The Machismo and T'bird come with a five-speed gearbox that shifts via a lever mounted on the left, familiar because it is the norm today, while the four-speed Electra sticks to the original right-hand-side gear-lever and convenient any-time-neutral stub. Lubrication for the gearboxes is grease, this archaic tech making the Bullets a rare breed today. Gearshifts are a matter of practice, with too much of a mechanical feel. The Electra gearbox is noticeably smoother than the other two bikes, but all are plagued with false neutrals and a poor feel.
Bullets are famous for their oil-dribbling engines and owners will be well advised to keep a tray beneath the bike each night to avoid a stained garage floor. The culprit is poor crankcase machining tolerances, but most Bulleteers know and turn a blind eye to this.
The entire gamut of changes by AVL has, astonishingly, brought in no increase in power and torque, though Performance is noticeably brisker on the Thunderbird and Machismo. Our acceleration runs to 60kph from rest found the AVL engines giving the Machismo and Thunderbird a healthy two-second advantage over their red sibling. This increased with higher speeds and was also reflected in overall better figures for in-gear roll-on acceleration.