His first major race as a driver was the 1907 Isle of Man Tourist Trophy. His Darracq retired early, owing to axle failure. This involvement with the closely related Sunbeam, Talbot and Darracq marques continued throughout his career. In the same year he also took part in the Belgian Grand Prix at the Circuit des Ardennes.
Around this time he acquired space in a disused pub, 'The Bald Faced Stag' in Putney, London as a base for his motor-racing exploits.
From 1913 he was an official driver for Sunbeam, along with Henry Segrave. Sunbeam's engine designer, Louis Coatalen, became a friend and assisted his motor-racing career, driving Sunbeam or Talbot cars.
His experience in the 1912 Manx Tourist Trophy led him to develop a more reliable spark plug. The innovation of the KLG spark plug was its use of mica as an insulator. This mica was stacked in sheets and compressed by the centre electrode being tightened on a thread. These insulators gave more reliable performance than the porcelain ceramics used by others.
Production of these plugs began in a small way at 'The Bald Faced Stag', supplying other racers including Segrave and Campbell.
KLG plugs developed a particular reputation for reliability in aircraft use and were in great demand during the First World War. At the outbreak of war he joined the Royal Navy, but his work on spark plugs was considered to be more valuable to the war effort and he was asked to resign.
In 1919 he sold world distribution rights to Smiths, then sold up completely in 1927. He remained as a consultant.
KLG's reliability was particularly attractive to the land speed record contenders and their many-cylindered aero-engines, often with dual ignition systems. Segrave's 1,000HP Sunbeam required 48 spark plugs, a mis-fire amongst which could be very difficult to detect and replace on a windswept beach.
In time, KLG out-grew their pub and a fine building was constructed in the most modern of styles. At one time 1,500 people were employed there. Sadly the building is now demolished and replaced by an Asda store.
On 18 May, 1922 Guinness used the car to set new Land Speed Records at Brooklands: the Brooklands lap record at 121.54 mph, then the flying-start land speed records over a half-mile, kilometre, mile and two miles. The fastest record being 136.05 mph for the half-mile. These were the last land speed records to be set on a racetrack rather than a beach or salt flat.
In his final months towards 1937, he was described as suffering delusions and was admitted to a nursing home. On 10 April 1937 he was found dead in a bedroom at his home near the KLG factory, having apparently gassed himself.
He was buried on 14 April at Putney Vale Crematorium, alongside the KLG factory.
Return of a Racing Dream; THE HUMBER IS 100 - AND ONE MAGNIFICENT MACHINE WILL BE BACK FOR A SPECIAL CAVALCADE
May 26, 2000; HUMBER'S brief but memorable entry into the world of motor racing will be marked this weekend when a magnificent Tourist Trophy...