I think most quickie pilots will agree that the plane is fine except for the powerplant. Kohler was the first industrial engine mfgr. to come up with a 90 degree twin, so that's what I used. Midwest Super Cubs (MSC) has a long history of making these engines perform reliably so the basic CH 25 (25 hp) was slightly modified:
factory iron flywheel replaced with one duplicated in 6061 Al;
crankshaft extension machined from 7071 Al;
power take off is from flywheel end in order to keep cooling airflow as designed and reduce torsional harmonics;
governor assembly removed;
aluminum intake manifold replaced with plastic one from MSC'
ground-adjustable main jet from MSC
rotating assembly balanced, cam ground, heads ported & matched by MSC;
all metal parts except flywheel (has magnets) cryogenically treated by Cryogenics International;
Earls Performance oil cooler;
CH18 coils substituted for the CH25 Smart Spark so that engine can run without battery;
This Quickie had 300 hours with the Onan, and so far has 18 with the CH 25. Climbs 600 fpm @ 69 kias, gets over 100 mpg @ 73kias, goes 103 kias at 3600 rpm using 1.5 gph.
the firewall forward weighs 1 pound more than the Onan did, and has an electric starter. Briggs, Honda, Subaru, and now Yamaha all make a similar engine. Kawasaki's is water-cooled. Hopefully folks will use one of these engines and get the Quickie fleet flying again!.