Build your engine to match your fuel.
I first got that lesson back in the 70s when they stopped hi-test and I was driving a 11:1 1970 351C Torino. My street legal KTM 125 often finds itself at a one pump general store, forced to swallow 87 octane. Slight mods have it able to run on 87 octane and still do 140kh (87mph) and climb any hills at highway speeds. On 125cc!
How do you do this?
1) Compact nearly spherical combustion chamber centered around the plug (exhaust valve in a 4 stroke).
2) Lots of Quench/Squish area to prevent detonation, 50% is a ballpark figure.
3) ~0.040"/1mm squish gap and a shape that inspires continued turbulence in the combustion chamber.
4) Port/valve timing that "bleeds" compression pressure at low rpm and increases with RPM.
5) Retarded spark timing because the compact turbulent faster burning charge does not need so much lead.
6) fine tune your plug heat range and compression ratio if needed.
That 11:1 351C required pocketed pistons (I was a machinist) that reduced the compression ratio to 10.5:1, reduced squish gap, high overlap cam with altered timing and backed off ignition timing. This is that same engine (Torino got rusty) in a Maverick on 87 octane:
The KTM 125 was easy.
Raised base gasket and dropped head, essentially raised all the ports 0.010", & ign timing.
I lost a tiny bit of low end torque and gained a tiny bit of top end, all on 87 octane.
Work on the Blaster discovered that shaving anything off the stock head or basegasket was risky for detonation. I have to thank JoeAK47 for help and sharing information on head shapes and squish gaps. The stock Blaster squish gap is 2-3mm and the head volume around 25cc IIRC. With the right timing, chamber shape, squish gap and porting you can run as low as 18cc on 87 octane (if built with that in mind) and still make great power.
My son and I have 4 Blasters, a Banshee and 4 KTMs (125, 250, 300, 380) floating around here.
All run on 93 octane and several have been "de-tuned" to run on 87. You don't give up much.
Service station premium 93/94 octane fuel is much more readily available and reasonably priced than Avgas or race fuel. It stores fairly well up to 3 months in a sealed can. I hear your stuck float issues, but I have a problem blaming it on premium fuel and using $5/gal fuel as an answer. Most guys around here who are using race gas or avgas are doing it just for bragging rights. Besides bragging they also have excuses for why it is never running right "today". Patches and work-arounds have their own way of compiling problem.
Solve the needle valve/float problem (clean tank, new filter, new parts etc) and you can run fine on premium fuel.
Steve
