A lot of hot air is devoted to “what fuel to use?”. Much of it is really quite unnecessary. Here’s the basic facts:
- Octane is a rating, I.E. 91 = Premium while 87 = Mid Grade. It is actually a measure of the resistance to detonation (aka ‘knock’, ‘preignition’ or ‘dieseling’) under compression. The higher the rating, the higher compression you can run.
- With high compression, lots of ignition advance and high octane fuel, the result is more power generated. Pick any one of these factors on it’s own, and you get no advantage and very possibly serious engine issues. For racing, high compression, premium fuel and advanced ignition work great. That’s for a motor that will be rebuilt frequently and not operated in stop/go traffic situations. For road riding in stop/go traffic and even at the rather modest speeds of touring, that same motor/fuel would not be a great choice.
- If you do some research on this discussion online, the burning characteristics on higher octane fuels are surprisingly different that low octane fuels. But it makes sense that if high octane fuels resist preignition, they burn slower and hotter at peak power. Low octane fuels burn fast, thereby developing their power in a short time-span. Who knew?
For road riding & touring: - Engines with 10:1 or higher compression NEED premium fuel, unleaded or not, to avoid pre-ignition.
- Engines with less than 10:1 compression run fine on unleaded regular gas or “mid-grade” gas.
High compression motors generate more heat on the compression stroke than lower compression motors which will cause ‘pre ignition’ if you try to use low octane fuels.
High octane fuels are more resistant to pre-ignition BUT a low compression motor will develop LESS power with high octane fuel than the same motor running premium!
Don’t believe me? That’s OK. Search the Internet, there’s tons of well researched info on this.
About Leaded vs Unleaded Gas. If you ever work on a vehicle that’s been sitting with leaded gas in it, you’ll find that gas congeals into a brown goo called “varnish”. Unleaded gas tends to dry into a white powdery material.
To avoid fuel degradation issues with unleaded gas, throw in about 1/2 cup of SeaFoam or Stabil fuel treatment whenever you fill up your tank – that’s it. Then your bike should be fine even if it sits in storage through the Winter.
There’s always an exception! Unless your motor is over 10:1 compression, using high octane fuel is wasted on day-to-day driving – with one exception. If you have a lower compression motor that’s accumulated lots of carbon, it may be prone to preignition caused by the carbon becoming very hot in the combustion area, which can ignite mid grade fuel, causing “knocking”. If you switch to premium, your power will go down but doing this will protect the motor. If you take that motor and run it hard with premium, you may reduce the carbon build-up to some extent, allowing you to return to midgrade.
Ethanol fuels react badly with old original gaskets and O rings. However, you should rebuild fuel systems as part of refurbishment or restoration in any case. Typical modern O rings, gaskets and hoses involve materials which are often referred to as “Buna N”, “Viton” or “Nitrile”.
We’ve had ethanol for quite a while now, so manufacturers generally plan for it. When sourcing fuel system materials, read or ask suppliers to confirm that their products are OK for use with ethanol fuels. The answer will almost certainly be “yes” because that’s been the standard for these items ever since ethanol was first mandated in over-the-road fuels.
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