The exhaust pipes had been changed on this Bonnie America and the owner brought because it wasn’t running right and he suspected poor fuelling. We ran it up and it was bad; so we put a new set of spark plugs in (it’d just been dealer serviced, apparently…) which at least cured the misfire, and meant we could get on with the mapping.

With the pipes it needed more fuel, which we added. We also modified the airbox by removing the sound deadening snorkel – it’s made of soft rubber and when you accelerate it closes up!

Rough running Bonnie down to old plugs, an ECU remap sorted the fuelling for the pipes.

Rough running Bonnie down to old plugs, an ECU remap sorted the fuelling for the pipes.