KX Riders
General => In General... => Topic started by: FuriouSly on January 08, 2007, 05:12:43 AM
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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.
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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
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Mine liked LL100 + Amsoil Pro @ 100:1
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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)
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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.
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avaition fuel has a lot more oxyen to make up forlack of o2 at high altitudes
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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.
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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.
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avaition fuel has a lot more oxyen to make up forlack of o2 at high altitudes
Avgas also has de-icing chemicals in it.
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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.
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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.
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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.
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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
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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.
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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?
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Update: I went back and added some info to the original post in GLOW
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Lead is (was) added to fuel for a number of resons. it changes the octane of the fuel and it works as a cushin on impact (not to be comfused with lubercatioon). there are 2 common ways to messure octane, RON (Research octane number) and MON (mechanical octane number). usually at the pump you will see them averaged, ignore it. pay closer attention to MON (usually the lower number) that is the only one your motor will notice.
2 strokes and old 4 strokes love leaded fuel. if you use leaded fuel in modern 4 strokes you can cause a lot of damage.
~steve
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Thanks for the clarification.
I had posted some questions before about jetting, because I was/am getting some surging. Do you think that running higher octane and leaded gas will help smooth that out?
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Does the leaded gas cause a carbon buildup greater than what you would normally get?
Yes and No. On a well built/maintained two stroke motor that is properly jetted with a good quality premix at a ratio of 40:1 or 50:1..... you might tell that the leaded has a little more carbon build-up. BUT, on 90% of the 2S bikes out there there is so much left over products of combustion that you can't tell the difference in buildup. Cheap premix at 24:1 ratio, leaking crank seals letting oil into cylinder, over oiled air filter leakage, and not tearing down the cylinder to scrape out a seasons worth of carbon build-up causes more issues with buildup.
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?
You can easily switch back and forth when needed, just make sure you keep the premix ratio correct. But, once you try some race gas... even at 50/50, you will have a tough time going back to 91 unleaded. Your bike will just not be as snappy.
Do you recommend only using pump leaded, or would an additive be fine?
True lead additives do help raise and stabilize octane in unleaded fuels. BUT, in high performance motors like a KX 2S, the unleaded pump gas just is not engineered with the high energy chracteristics in the fuel from the start. SO, you may take the 91 unleaded to 95 octane with an overdose of additive, but the fuels designed energy level will still be less powerful than VP C12 mixed 50/50 with 91 unleaded. Most true lead additives can be multi dosed to increase octane but usually only by 2 pts per dose.
I had posted some questions before about jetting, because I was/am getting some surging. Do you think that running higher octane and leaded gas will help smooth that out?
Yes and No.... What bike and year do yo have? Whens the last time it has been rebuilt? Top end and Bottom end with new gaskets, crank bearings and seals? Is it jetted right on? Any air leaks at the reed block or intake boot? Surges at idle or when you let of the gas rapidly after full or 3/4 throttle? So many variables to take into account. Funny, but these motors are very simple and yet can be very difiicult to fine tune. Eveything affects everything when it comes to motor performance.
Sly
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Sly - Thanks for the replies.
The surging happens when I let off from around 3/4 throttle. While it is surging, if I feather the gas about 1/8 throttle or less "if that is possible", then the surge instantly stops.
I tried using ether to find a leak, but did not find any. I do have a torque reed spacer, but again, no leak. I even rejet it richer...especially now that it is winter, but even with the richer jets in 50 degree weather, it was surging.
I will have to try this fuel stuff out..thanks for the info!
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WOW, is there anything as good but less expensive than this VP C12 race fuel? This stuff is like 10 bucks / gallon! ...that is what, 5 flicks of the wrist? lol
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WOW, is there anything as good but less expensive than this VP C12 race fuel? This stuff is like 10 bucks / gallon! ...that is what, 5 flicks of the wrist? lol
thats why i usually rike other bikes, the k5 is for speacail ocations. :wink:
as for switching between fuels, you will have to re-jet the bike to make it run correctly and if you are using fuel additives be careful most aditives DO NOT alow your pre-mix to mix. i am not positive but i think the type of alcohols thay use.
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Which VP fuel is better to run @ 50/50 with pump gas? C12 or U2
I'm not clear if the C12 is leaded or not. My K5 was jetted close stock @32:1/pump gas but now I'm waiting on my top end to come back from eric gorr with port work plus a PC works and V2 reeds and curious if I should make a changes richer or leaner before I start it with C12/U2 and syn oil at 50:1.
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run a 50 pilot jet and 175 mian in pwk carb with u2 gas b9 plug yes c12 is leaded
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Only fuel I could find local was the C12. I'm running the beast on it straight for now at 50:1 with mobil 1 racing 2T. Runs great but.........
I'd like to get some U2 to compare then stick with the best from now on.
Question is now my jetting is 55, 165, 2.5 turns, 3rd clip. What changes would I have to make with U2.? My riding averages around 700 feet elevation.
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Redlined:
but now I'm waiting on my top end to come back from eric gorr with port work plus a PC works and V2 reeds
Question is now my jetting is 55, 165, 2.5 turns, 3rd clip. What changes would I have to make with U2.? My riding averages around 700 feet elevation.
So you put Gorr's top end on? What type of porting if any? Up compression? If mild to stock comp then U2 would be fine... its 101 octane leaded.
run a 50 pilot jet and 175 mian in pwk carb with u2 gas b9 plug - stewart
Sound good if mild to stock comp with reeds and pipe. 700 feet may need 55 pilot and needle in the middle clip. You ride and break it in already? IF not, 182 main fat-start it at idle with little blips of throttle for about 3-5 mins until warm and shut down-let cool completely. Do one more time. Then take it out, warm it up and run it HARD WOT on some slight incline hills to set the rings. You'll love it.
Sly
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Hey Sly,
I had already broken in couple days ago using the steps outlined in the complete top end rebuild thread. Except I heat cycle 3 times before I rode it. The piston/cylinder wall clearance slightly under the minimum.
I'm riding today so I'll try the clip, and pilot change to see what happens.
I had EG do his best mid to top end port work. I don't ride alot of tight areas so low-end isn't a concern. Compared to stock it's definitely a little softer off idle but the hit is much harder and seems much broader and also it has a very strong over rev. Before it would sign off flat.
I didnt measure the compression yet. I did check the squish. It was 1.4 with stock base gasket and the .2 metal factory head gasket.
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I cant get leaded fuel here where i live, so i run on shell v power, its got the highest octane rating around here, is it possible to a lead substitute? (I cant get lead either) will lead substitute have the same benefits as regular lead?
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I myself have never been a fan of the lead additives/octane boosters, though some do show slight improvements...they're just not worth the money...otherwise you'd see a lot more of the motorsports industry using them.
If you suspect you're pinging, and can't get good quality fuel...then you could always have your head re-cut, so it'll run strong on the best fuel you're able to get.