This is a well-tested in competition and extensive experimentation, and repeatable with at least a dozen engines actually tested in flight on a variety of small 35-sized planes (Skyray 35, Flite Streak, Medic, very fast Ringmaster):
- Stock 20FP ABC
- Stock Muffler
- Stock Venturi
- Stock Spraybar
- APC 9-4 or MK-Custom 8.5-4.5
- Low-profile Uniflow hard tan, no pressure
or Sullivan SS-4 clunk tank, set up per instructions (except third tube for overflow, convenience only), suction with muffler pressure
- Thunderbolt 4-cycle
or R/C plug
- Sullivan "Crap Trap" 2-stage filter
10% Champion fuel
- Skyray/Flite Streak-size model
- 60-62 foot .015 stranded lines
Lap time will be between 4.6-5.0. Can be slower or much faster if desired. Ringmaster will be flying about 3.8-4.0 -second laps on 60' lines at proper setting with 9-4.
No break-in required, two-three tanks on ground desirable. to stabilize fuel consumption. Set at about 11,300 on the ground, or peak out and then back off about 5-6 clicks until its noticably off-peak. First flight may sag on hard outsides, will fix itself in a few flights. Fuel consumption will be close to 3.5 oz on first run, will decrease to about 2.4-2.5 oz after about 15 flights, then stabilize.
In-flight setting in level flight should be a rich-medium 2-stroke. If airplane is too fast, reduce venturi with Bru-Line "fine" air filter. If too slow (very unlikely), lean out, or move to 15% nitro. Can be run near peak with little chance of damage. Speed can be tweaked slightly with needle, but running a 4-stroke in level flight will likely result in excessive speed variation in flight. In extreme cases (Ringmaster), speed can be reduced with ST needle, but this is not necessary for run stability, just power reduction. Use 15FP on Ringmaster instead. The engine will spin much more prop. But don't. When in doubt, add less prop.
Things NOT TO DO:
run more load than APC 9-4 prop
run hard tank with pressure
run excessively wide hard tank
add head gaskets
plug up boost port
This will work, there is NO DEBATE that it works, it's not an experiment. If for some reason it does not work, look for some reason aside from engine setup -like all the usual suspects, fuel lines, crud, tank leaks, etc. If you want to experiment, by all means go ahead, but this is good enough to win any advanced contest and most expert contests, and is a completely turn-key operation that repeats from engine to engine. AND IT DOES IN FACT PUNCH THROUGH THE WIND BETTER THAN MOST OTHER SETUPS ON SIMILAR AIRPLANES.
Note that this will more-or-less work on the 25FP, but not as reliably, in my experience. The 25 occasionally runs away unless you use a filter or reduced venturi, which is fine since a properly-running 25FP will GROSSLY OVERPOWER many of these type of airplanes and you will need to slow it down anyway.