On new scooters, with all parts working well, with a KISS ignition system, and average engine setup... You may never "See", or "Feel" a difference.
However, that is not to say that nothing is happening.
The 90+ octane that most gas stations use, is better. (Sometimes only modestly better. Buying cheap gas, is cheap gas, high or low octane. Buying good gas shows better results.)
What will happen?
Low octane = slightly less HP. (At the 8-12 HP you have, you will not notice 0.2 HP gain.)
Low octane = less fuel burned, or more fuel unburned, potentially, when it happens. (This will cause more exhaust burn after the piston, carbonization in the piston and exhaust, will run cooler internally but overheat the exhaust, produce more NOX fumes.)
Low octane = Less MPG, if your scooter is designed for 90+, and you go for cheap stuff. (Requires more fuel to get you the same distance, since it burns less complete, may be igniting before expected, and burns in the exhaust. Igniting before expected, pushes against the rising piston that is still trying to compress. AKA PING. Still burning in the exhaust, causes excess back-pressure, limiting the ability for exhaust to exit from the explosion pressure. AKA EXHAUST BACKFIRE. Both PING and EXHAUST BACKFIRE are not always loud enough to hear, or feel. You only hear or feel them when they are extreme. Any occurrence will slow you down before you hear it.)
On the contrast...
High octane = More complete burn. (Exhaust carbon is all airborn dust, not surface condensation.)
High octane = Hotter piston temps, cooler exhaust. (This can have negative impact, if you get into 100+ octane. The 90+ octane gives a more balanced internal/external temp, where the scooter is designed to be.)
High octane = Less preignition. (You will minimize or eliminate PING which will result in a feeling of power gain, mostly on high performance, or older engines, where piston wear does not allow excess pressure to escape on compression, or at high speed compression. EG, when you accelerate, and ride near MAX RPM, which is where scooters spend most of their time.)
Essentially, you can set your carb to run slightly leaner, or with less fuel, since you are burning more of it, and since less is needed, for the same power. It will not actually be lean, just less fuel, it will be the same volume of combusted mixture as the lower octane fuel.
If you don't make any adjustments... you will not get more MPG. (High performance engines auto-adjust, with injectors, and O2 sensors that determine rich/lean, by measuring exhaust gas temps. Scooters need manual adjustments to notice change. That is why everyone keeps using bigger jets, they choose to use the cheap stuff, which needs more fuel, and the scooter is not designed for. However, they kiss the MPG goodbye, at the gain of more power or speed.)
Signs you will notice with both...
Low octane (87 and lower):
- Fast rusting exhaust (Spiders and flakes, rusts all over)
- Hard to ride at top speed, (Power loss)
- PING sound, (Hollow knocking)
- EXHAUST BACKFIRE, (Pop or bang)
- Tons of carbon in exhaust
- Sheet of black carbon on spark-plug and piston head and valves
- Typical strong exhaust smell (More NOx, less CO2)
- Difficult to start when cold
- Less responsive to throttle
- Requires larger jet, and more air, (Resulting in more ping)
- Non-ignition, (Empty poof sound through exhaust.)
- Oil stays cooler, (Can use thinner oil 10W30 - 10W40)
High octane (98 and higher):
- Slow rusting exhaust (Blisters slowly in time, rusts underneath)
- Easy to ride at top speed, (Power gain)
- Little carbon in exhaust
- Tan or brown fuel sediment on spark-plug and piston head and valves
- Clean exhaust smell (Less NOx, more CO2)
- Easy to start when cold
- More responsive to throttle
- Requires smaller jet, and less air
- Oil gets hotter, (Requires thicker oil 10W50, 20W40. Thinner oil will carbonize and boil/steam away.)
Once again, those are EXTREME separation...
Using cheap gas, as in from a mom-n-pop fuel station...
86 and 93 are possibly the same fuel, you will not see a change.
using those same fuels from a mid-grade fuel shop...
86 is positively not the same as 93, but it may not be better.
using those same fuels from a high-grade fuel shop...
86 is like water, 93 is like jet fuel... day and night notices.
That 86 from the mom-n-pop, is like 80 from the high-grade fuel shop...
That 93 from the high-grade fuel shop, is like 120 at the mom-n-pop shop. (They meet octane levels, but do not provide the "Additives", or expensive processing, to go with the cost.)
www.offroaders.com/tech/octane.htmdnr.louisiana.gov/sec/execdiv/techasmt/ecep/trans/b/b.htmI could pluck more data, but it all says the same thing... though not so clear...
If your scooter requires 90+, and you use lower, you will NEED to modify it, or suffer with less MPG, less power, PING, etc...
If your scooter requires 86+, and you use 90+, you will NOT see better MPG, though you may see other gains and losses. You will STILL NEED to modify it, or suffer with the results.
ALL 4-stroke scooters are ALL 90+, by design. (If you still have your English converted china-manual, the book will say, or the fuel sticker will say, "Use 90+ rated, Unleaded fuel".)
Until these things come with computers, and oxygen sensors and computer controlled fuel injection... You don't have a real choice.
