I never thought of myself as much of a 'practice' rider. Time is tight, lots to do: family, work (self-employment work-life balance/imbalance), so I make time for the races, but not always the practices. 2020 has been different. There have been no races, so I've craved the practices.
At the couple of practice days I've attended I've had a bit of time to talk to people I don't always get time to speak with either because we're busy racing, or racing on different days, or pitted in different ends of the paddock. This is the case with Mike Fisher, so I made the time to have a better look at his Champion Bultaco.
The first thing I noticed was the massive, modern AIM digital dash, designed for karts. Mike was having problems with his bike at the practice, he thought it was a reed-valve sealing issue, but it's normally very reliable for a 40-year-old two-stroke racebike, and that's down to Mike's research and development. He explained he uses the dash as more of a datalogger than a regular tach. He has a sensor in the exhaust for measuring exhaust gas temp (EGT). Mike knows which temperature the gas reaches when it causes pre-ignition (pinking, knocking) and the piston is at the risk of melting. Knowing this allows him to change the carb jets. There is another sensor that measures cylinder head temperature.
'The dash usually sits under the seat and can download to a laptop but for practice days I can put it up on the handlebars to see RPM,' explains Mike. 'I bought it to understand gearing and to provide tuning information when I get round to trying to build a super quick motor. These old air-cooled, two-strokes get detonation above 220C head temp and are happier below 215C peak readings. Peak EGT is in the 625-725C range dependant on gearing and tuning.
'For gearing I can look at max rpm, rpm in the corner and CHT/EGT. For example undergearing pushes the motor into over-rev and risk of detonation or worse but keeps the revs up in the powerband in corners.'
The bike has a new alloy tank. Mike made the pattern from cardboard, then cut it out of alloy, before his fellow DTRA Vintage racer, Rick Bearcroft, welded it up for him. He then had a motocross graphics company make the stickers. It's a neat job.
'The frame is a Champion or more correctly Schwerma Products. Doug Schwerma built and raced Yamaha twin and Kawasaki triple drag bikes in the late 60s/early 70s, he tuned Yamaha TD road racers, tuned Yamaha DT1s and built DT1 offroad/MX frame kits. He then built flat track frame kits for DT1s, Bultacos etc. under the name Schwerma Products,' says Mike. 'My frame is 1972 it predates the use of the Champion name. Champion went through various incarnations after Schwerma’s suicide following financial difficulties, expensive litigation defending his designs and, it would seem, cocaine (it was 70s California). There are photos of an A&A Racing Jim Odom bike using the same frame as mine.'
Mike explains the history of the Astro name, 'It followed the success at the Astrodome with a Sherpa S framed bike with a 250 Pursang engine. The Champion-framed bikes that Mike Kidd, etc., rode came later. One was sent to Spain to be copied to create the later chequer block production Astros. But it would be wrong to say it is a copy of the Champion. The lower engine mount is copied and presumably the geometry but the construction and materials are very Bultaco (heavier gussets and MIG welds) compared with the Champion (4130, thin folded gussets, TIG welds).'
There are more two-strokes joining the Sideburn-sponsored DTRA championship, with Danny Williams and his Astro (featured in Sideburn 41) and Steph (Sideburn 35 cover model) and her Bultaco joining the class regulars of Sean Kelly (Suzuki), Lucia Aucott (Ossa) and Darren Legg (Yamaha).
Go to Dirt Track Riders Association for more info on the classes.