The YZ250f 4-stroke, will put out around 42 Hp ; how much engine weightBack in the early days of US ultralights cut down motorcycle 2 strokes were pretty common.
The YZ250f , 250 cc , is a 4-stroke ; and the kawasaki kx250f , isThe small 2-stroke motorcycle engines are not designed to survive at the "duty cycle" or power level that is used on aircraft.
Mathew, unfortunately due to stall speed issues (real speed checked in flight) neither the Turbulent or the Jodel D9 meet the SSDR rules, neither does the Chilton! This was a finding from CAA and LAA at the time of the weight increase on the category.Keep in mind that the OP is discussing a UK single-seat deregulated type (SSDR) so a maximum takeoff weight of 300 kg/661 lb and a stall speed under 35 kt/40 mph/65 kph, so a very different beast than a Part 103 ultralight. I would suggest a basic design capable of meeting the SSDR specs with a modest VW but repowered with an industrial engine and an Ace redrive. The MiniMax V comes to mind, and because there is an allowance up to 390 kg for amateur-built aircraft permitted before 2003 you might also look for an derelict Luton Minor, Druine Turbulent, or Jodel Bébé to restore as an SSDR type.
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I see you willing to keep costs down and need for technology too. My advise would be: go for car-towed gliders. It does not have to be a HUMMER to pull the glider up. We used a old Renault to tow our Bi-Swift (two-seater). Theere are good plans on the internet of primary gliders. Mike Sandlin has very good and proven plans. Goat and Bug is a good glider of him.
Gliding is pure fun. OK, you need to be a team to have flying days. A pilot, somebody in the car, somebody maybe at the wingtip (might be that it is not needed on GOAT and BUG). The flying is more pure and you will have NO trouble with neighbours who complain about your noisy lawmower engine on your airplane. So ... go soar the sky in a glider and have fun at the lowest cost possible.
Disadvantage: you need a large field to take off due to the length of cable and the car needing to ride. If you have a abandoned road, you are very lucky.