Fixed some areas below in
GLOW...
Hey all...
I did some searching and did not find a topic that would encompass the subject of "Fuel" as relating to our beloved motorbikes... We talk about getting the best performance out of our KX motors all the time so I thought that fuel has something to do with that !!
Jetting, premix, altitude, humidity, temperature, porting, spark plugs, compression, exhaust pipes, reeds, reed blocks, flywheels, ignition, etc etc etc.... all these have fuel in common.
First off, two-strokes have different fuel needs than four-strokes plain and simple. To get the 4S out of the way, they can run out of the crate on unleaded pump gas (87-91) and make optimal power in stock form for the masses. Enough said on the 4S, let's make that another topic.
2S are a bit different. In their nature to run good and make power,they are a little more needy on the requirements of the fuel they use. Quick and easy, a 2S doesn't have valves and four strokes to a cycle to remove the combustion products left behind that cause detonation and/or pre-ignition. 2S need a high energy fuel for the power with a high octane to prevent the side effects since it makes power on every stroke and not "combustion process" efficient either. Lots of products of combustion floating around which cause the detonation and/or pre-ignition.
Gasoline mumbo jumbo: RON, MON, octane, MTBE, leaded, unleaded, race, avgas, etc etc etc. Here are some basics to know:
1. The yellow label on the gas pump is not the true octane number that we (motorists-crazy jugheads) should use in reference to true octane in the fuel. 87 unleaded is actually around 85. 89=87 91=88 in America. Euro 95=92.
Even though the label says RON+MON/2 = octane level (for average daily driver automobile use), it is a little lower pertaining to the above average use requirements (i.e. high performance 8,000 RPM motors and up). Octane ratings refer to the ability of the fuel to restrict knocking (predetonation).
Aspirated 2S motors with competition level carburetored motors require more octane to perform optimally.
2. Unleaded is not as good as leaded for 2S. The properties of lead are the most desirable to stabilize the fuel energy and octane to help reduce the side effects of detonation/pre-ignition in fuel. Unleaded has to use alot more chemistry to do the same and still comes up short.
3. Fuel stored in any plastic container for long periods of time will lose its potency faster than you think !! That is your bikes gas tank, your trick $30 VP can, even the wal-mart special. Fuel breathes through plastic and can add moisture to the container in cold/humid climates. Metal gas cans are the best for storing fuel for long periods (months).
4. Fuel loses its potency over time no matter what container you store it in. No real numbers here, but a rule of thumb would be 1 octane point a month... but you get the idea.
What does this mean? Here is what I use to help my friends understand the
importance of fuel in very basic terms:
1. What size motor in cc's? 125(More Compression), 250, 500(Less Compression)
2. What compression do you have? Stock, Medium, High Performance.
3. How do you ride and where? Cruise or WOT-desert, woods, track, dunes.
4. How much money do you make? hehehe... race fuel is expensive...
So, if you have a stock 250 2S and cruise in the woods=fresh 91 octane unleaded with
quality premix would be the least you should use with a BR8 plug and jetted right.
Have a KX5, ride in the desert, with a little more compression, reeds, and a FMF pipe=fresh 91 octane unleaded with
quality premix should be the very least... probably should mix 50/50 to get to 95 octane (108 octane leaded like VP C12 mixed with 87 octane unleaded will get you to about 96)
Oh, you have a KX5 that's ported, bigger carb, high compression, and the kitchen sink thrown in=straight leaded race gas with a minimum of 100 octane (if your comp ratio is under lets say 10:1) with
quality premix. The so called race gas you can buy at the pump ($5 a gallon) in most places is really just unleaded 100 octane which amounts to about 97 octane through epa geek chemists. Anything running with moderate compression should have a minimum of 100 octane, leaded is better.
True leaded race gas with a rating of 108, 110, 112 octane will all do in a high performance motor that we are talking about right now. And yes, that is just about everyone reading this right now. 2S motors are high performance in their nature. Higher octane does not mean more power in that 112 will be more powerful than 105, it just means that your motor might need 110 octane to keep from knocking (detonating and/or pre-igniting) in relation to how built up
(compression) your motor is.
The energy in the leaded fuel above is pretty constant, just that 108 octane might be all you need and it's usually less expensive as well. You having problems with poor performance with your mildly modified motor?
Try some race gas and work your way down the octane levels until you find your bikes liking and fork out the dough to keep it running there.
From a motor?s standpoint,
leaded fuel doesn?t detonate as easily as unleaded fuel, so you?re able to use a higher-compression motor settings. When more compression is run, the bike has greater acceleration. Octane, the rating of a fuel?s ability to resist detonation and/or pre-ignition, is a critical factor in the performance of a modified motor. The infamous "lead" component is the best octane improver on the market, from a cost and benefit standpoint.
With lead you can use the higher energy components, maintaining that overall good combination.
I personally run leaded 112 race gas straight. My KX5 is built up a bit with motor/carb work and most of the doo dads. It is run at the dunes exclusively and just won't run on 100 octane. It pings and overheats... the trademark side effects of LOW OCTANE.
OK, I must say again.... this is my basic talk on fuel and I must apologize for the length. Now I hope my peers will add and correct this topic so that we can all learn and expand our knowledge of this volatile subject. Special thanks to
"Arigato" for the many classes on motors and fuel while sitting around the campfire drinking Vodka and RockStars at the dunes.
Peace... Sly
Addendum added for clarification....
All two-strokes need premix oil in the fuelUnleaded Fuel has no lead in it and generally speaking cannot produce high energy/power levels for high performance motors. Most unleaded fuels are unable to reach over 100 octane. Adding lead to 91 octane pump gas will help raise the octane level but the fuel's initial design will not have the energy needed to effectively use the benefits of the higher octane levelLeaded Fuel of course has lead in it and generally speaking does not come in ratings below 100 octane in most areas. EPA has long since deemed the fuel unhealthy, so the general population has been converted to unleaded... hence the surge of four strokes. The leaded race fuels available today are high energy fuels that need higher octane levels. High compression motors need high energy fuels and high octane.The labels 94 leaded and 94 octane can be confusing. 94 leaded means 94 octane fuel that uses lead to help stabilize the octane for knocking (detonation/preignition). 94 octane can be leaded or unleaded, it's just the octane rating of the fuel.
