Author Topic: "Fuel" needs for the Two-Stroke  (Read 12813 times)

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Offline FuriouSly

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"Fuel" needs for the Two-Stroke
« on: January 08, 2007, 05:12:43 AM »
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...  :-P

   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 fuel

Unleaded 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 level

Leaded 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.

« Last Edit: January 25, 2007, 02:50:32 PM by FuriouSly »

Offline kx666

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Re: "Fuel" needs for the Two-Stroke
« Reply #1 on: January 08, 2007, 05:11:12 PM »
i am soo glad i didnt have to post this, that is a lot or typiung. and computers seem to not like me when i type a lot...

sly is right on, there are many misconseptions on fuel. i used to use 76 race fuel and it was awsomne, then one day about 5 yrs ago? there race fuel vanished. when conoco bought union 76 they cut off the race fuel divition (they thought it was a wast of $$). all oth the chemists started there own fuel company named "Rocket Brand Fuel"
the company its self is very helpful and gave me a ton of info as well as there fuel is awsome (so far, i have a few rides with it but it is hard to find i have to go to OR to get some)

~steve

Offline Paul

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Re: "Fuel" needs for the Two-Stroke
« Reply #2 on: January 08, 2007, 05:41:52 PM »
Mine liked LL100 + Amsoil Pro @ 100:1

Offline kx666

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Re: "Fuel" needs for the Two-Stroke
« Reply #3 on: January 10, 2007, 04:56:01 PM »
wow 100 to1, mabe i am beeing too old school but i dont have the balls for that.. i have been doin' the 40:1 to 50:1 and it took me years to try 50:1 (recomended by dumonde)

Offline 5dracing

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Re: "Fuel" needs for the Two-Stroke
« Reply #4 on: January 11, 2007, 08:21:50 AM »
Mine liked LL100 + Amsoil Pro @ 100:1

Paul,

I was told by a fuel guy not to run Avgas in anything that reved higher than about 3000 rpm's. He said the fuel was not formulated to run at any rpm higher than that. I was going to run this because I was at the airport alot when I was getting my pilots certificate. We used to get it for our fire pumps because of its stability.

I'm confused.
The torch has been passed; Father to Son. He is faster!!!

Offline kx666

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Re: "Fuel" needs for the Two-Stroke
« Reply #5 on: January 16, 2007, 08:52:13 AM »
avaition fuel has a lot more oxyen to make up forlack of o2 at high altitudes

Offline musturbo

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Re: "Fuel" needs for the Two-Stroke
« Reply #6 on: January 16, 2007, 12:43:43 PM »
i have been using sunoco 110 and bel ray h1r  @40 to 1 and all i have to say is it was like riding a different motorcycle!  crazy power at any rpm, easier starting, plug read great.
pin it

Offline KXcam22

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Re: "Fuel" needs for the Two-Stroke
« Reply #7 on: January 16, 2007, 03:58:29 PM »
In my race years in the late 70's I ran a mix of 100/120 avgas and unleaded regular with 85:1 Belray Mc-1.  Was a good combination in those no race-gas days.  The high octane gave a noticeable boost in throttle responce.  I am lucky that I can get 94 octane pump gas doen the road.  The KX seems to like it, but I have mellowed to a conservative 60:1 with the Mc-1.  I'll bet though that if I was running in sand I would be runnign race gas all the way.  Cam.

Offline Danger4u2

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Re: "Fuel" needs for the Two-Stroke
« Reply #8 on: January 17, 2007, 02:08:12 AM »
avaition fuel has a lot more oxyen to make up forlack of o2 at high altitudes

Avgas also has de-icing chemicals in it.
KX 500 Rider

Offline gowen

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Re: "Fuel" needs for the Two-Stroke
« Reply #9 on: January 24, 2007, 01:15:03 AM »
Speaking of fuel.. I still have a 55 gallon barrell of C12 sitting in my garage.. Unused and unopened. Guess it is time to raise the compression on my R1.

Offline raredesign

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Re: "Fuel" needs for the Two-Stroke
« Reply #10 on: January 25, 2007, 06:24:22 AM »
I was completely cought off guard about the leaded fuel.
Does this mean that you still use a 2s oil?
What are the downsides to using leaded fuel?
I am looking to get the most life out of my bike since I don't keep it at high rpms...I am hoping to have it last about a year between rebuilds.
I posted to the jetting section about the surging I am experiencing. It sounds like this could be a solution.

Offline Danger4u2

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Re: "Fuel" needs for the Two-Stroke
« Reply #11 on: January 25, 2007, 06:45:36 AM »
Does this mean that you still use a 2s oil?
Yes on the oil allways.

What are the downsides to using leaded fuel?
Bad on the environment and cost.
I burn 111 octane leaded fuel @ 5 dollars a gal.only because it's cheaper than 101 octane.
If I'm short of cash I'll mix 50/50 with 93 octane unleaded pump gas.

I am looking to get the most life out of my bike.....
Pull maintenance on your bike often.  Keep air filter clean , change trans oil allot.
Change radiator fluid and brake fluid at least once a year.
Do the cable lube and back brake pedal oiled just like the owners manual.
KX 500 Rider

Offline raredesign

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Re: "Fuel" needs for the Two-Stroke
« Reply #12 on: January 25, 2007, 07:35:41 AM »
Thanks for the response.
Does the leaded gas cause a carbon buildup greater than what you would normally get?
Are there downsides to switching back and forth, such as if I want to try it, or if I simply want to use it when I can?
Do you recommend only using pump leaded, or would an additive be fine?

I am not sure I understand the octane vs lead. In other words, what is the difference between 93 Octane and 93 leaded? Doesn't the leaded burn slower, so I really wouldn't need to use a higher octane? If that is the case, does that mean that lead can be a substitute for octane?

Thanks

Offline Danger4u2

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Re: "Fuel" needs for the Two-Stroke
« Reply #13 on: January 25, 2007, 08:25:16 AM »
I'm by no means a fuel expert.  Unleaded is just that, no lead in the gas.  When I had my 65 Ford truck motor rebuilt they installed valves that could handle the gas they make today, unleaded.  If you burn leaded gas in a new car it will clog the catalytic converter.  I've run pump gas in my K5 and it seems to not run as good as running the leaded race gas.  I think you should go back and reread the first post in this thread it will give you a better understanding of octane.
KX 500 Rider

Offline raredesign

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Re: "Fuel" needs for the Two-Stroke
« Reply #14 on: January 25, 2007, 09:59:14 AM »
I understand how octane raises the flash point so that the rod is at full extension when it fires, but is that the same thing that lead does?...or is lead acting as something different?