Two Stroke Motocross
Two Stroke Motocross Forum => Technical => Topic started by: wysguy on May 25, 2011, 10:10:04 AM
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I have a 2006 YZ250 and have been riding it for a couple months. It seems to run well, but I am coming from 3 previous 4 stroke bikes so I am not well versed in 2 stroke performance.
Two other riders that I know that have quite a bit more knowledge than me on 2 strokes say that they went through pistons within 5 hours on their YZ250's because they weren't running high enough octane fuel (race fuel). They both said they ran premium but recommended that if I continue to ride/race my YZ that I run race fuel, or at a minimum blend it with premium gasoline.
This seems like a huge distraction for me as race fuel isn't immediately available, not to mention expensive.
Maybe some background is helpful; I ride 2 -3 days a week all MX tracks. I race monthly in C and Vet classes, so nothing too fast, but still competitive. I am mechanically inclined, I rebuilt the top ends' of my 4 strokes in the past and am not afraid of rebuilding my 2 stroke now.
The bike runs well, the spark plug tells me the jetting is reasonable. I currently use Sunoco 93 octane with 32:1 S2 oil. I haven't pulled the head to look at the piston, but plan on doing that in the near future. I do however notice some odd sounds from my YZ but because I am not used to 2 strokes they may be normal. I cannot tell if it is detonation or just "2 stroke rattle".
Any advice?
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Bikes tend to last longer and happier using an octane of around 104. I buy some 108-110 and mix that 50/50 sometimes 60/40 with premium to keep it around 102-104.
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If I remember correctly, the '06 did run right on the edge of detonation with pump gas. I think Yamaha put a different needle in the carb for '07 to cure this. If you don't want to run race gas, check into the new needle.
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If I remember correctly, the '06 did run right on the edge of detonation with pump gas. I think Yamaha put a different needle in the carb for '07 to cure this. If you don't want to run race gas, check into the new needle.
A needle change seems much simpler, and cheaper, than finding race fuel to ride.
I appreciate the advice.
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Try the needle I guess but all my Rm's and my 04 and 05 Yamaha's almost always would detonate without at least running like 1 gallon 100 to 3 gallons 93, I am now running half and half, and sometimes totally race gas, but the price isnt much different.
There are 2 gas stations that sell 110 around me and its like $5.89 a gallon, hell 93 is like $4.09 a gallon right now.
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I would advise against using only pump gas. Most of it is 15% Ethenol, which will gum up your carburetor and your bike will not run well. Here I can get 109 octane for just over $10/gallon and 108 for just over $8/gallon.
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Every 2 stroke Ive had LOVED race gas. You can tell a defference from the minute you go to clear it out.
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Every 2 stroke Ive had LOVED race gas. You can tell a defference from the minute you go to clear it out.
yep
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I just found an old school gas station with non ethanol 93 ;D it's cheaper than most other places in town too. Gonna get me some of that this weekend.
As for race gas I have used it in the past on my YZ250, it needed it, my KX not so much, when I first got it, it would detonate occasionally on 93 but only if it was last weeks gas. Since I lowered the compression (with two high compression base gaskets) I haven't had a problem , the gas in it now is 3 week old 93, started it up yesterday and it ran fine.
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It's funny, here in Mass I can get away with 93 just fine. I've had my bike (2000 RM250) detonate, but only by jetting it too lean.
I'm not sure what our ethanol content is. I want to say 10%, but I'm not certain.
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My advice is not to use race fuel if you can get away without it. My reasoning is this: As a Vet C rider, the performance gain from the fuel will not be worth the added expense. You would be better off saving the pennies (nickels and quarters!) and putting the money to a riding clinic or school or a new set of tires.
The caveat of course is detonation and piston life. Be sure jetting is correct and you get good fuel. SAMS CLUB or the 7-11 down the street will not have the best quality pump gas. You might pay a little more, but in the long run, it is worth it. Also, at the more expensive gas stations, you stand a better chance of finding non-alcoholic fuel.
Back when I was traveling a lot to the races, I noticed higher gas mileage in my tow vehicle if I spent the little bit extra on good gas. It always worked out in the long run.
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It's funny, here in Mass I can get away with 93 just fine. I've had my bike (2000 RM250) detonate, but only by jetting it too lean.
Same here. Heck I have run 89 in my KDX before with no detonation, pinging etc. I wanted to ride and it's all I had here (I use the cheap stuff in the Craftsman tractor :D ) so I mixed it up and it ran fine. I do not race, but I ride hard.
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My advice is not to use race fuel if you can get away without it. My reasoning is this: As a Vet C rider, the performance gain from the fuel will not be worth the added expense. You would be better off saving the pennies (nickels and quarters!) and putting the money to a riding clinic or school or a new set of tires.
The caveat of course is detonation and piston life. Be sure jetting is correct and you get good fuel. SAMS CLUB or the 7-11 down the street will not have the best quality pump gas. You might pay a little more, but in the long run, it is worth it. Also, at the more expensive gas stations, you stand a better chance of finding non-alcoholic fuel.
Back when I was traveling a lot to the races, I noticed higher gas mileage in my tow vehicle if I spent the little bit extra on good gas. It always worked out in the long run.
Not to sound ignorant, but how do you tell which gas stations sell good fuel? I chose Sunoco because of word of mouth.
And yes, I have no need for the performance gain, the YZ250 is plenty of bike for me and the class(es) I race. I just wanted to treat it properly so it won't fail prematurely.
Thanks
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Last night I decided to pull the head off just to have a look at the cylinder. I could see no signs of damage from detonation, and I would suspect the jetting to be a bit rich although the plug likes just about right.
I am going to do a little scouting around to see if I can find a local station with race fuel as it is not a matter of the expense but more of the hassle to always have some on hand. I guess the 4 strokes have babied me and I am used to grabbing fuel on my way to the track.
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Again, just from my experience; Mobile, Sunoco, BP, Shell, (surprisingly) Hess - the name brands. My guess is that they have more at stake than the budget operators so make their franchises live up to a higher standard.
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Usually I mixed it 50/50 with 93 octane.
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Usually I mixed it 50/50 with 93 octane.
Same here. It actually saves me money in the long haul. Due to the fact of running only pump gas will more easily lead to a failure. For example, I have no idea how to clean a carb, and it costs me 60 dollars to get it cleaned... I'd have to clean it every 3-4 months if I'd want to keep my bike race ready. Not to mention it is more likely to cause a seizure. My best advice to anyone is to find a nice ethenol free station, hopefully 93 octane, and mix it either 50/50 or 60/40 (race gas/pump gas) and try to get a nice 102-104 octane. I would not use only race gas or only pump gas. They are both more likely to wear your engine out sooner. I haven't experimented with octane booster though. I would imagine if you found some Ethenol free fuel and used octane booster to mix it to 103 that would be the best and cheapest.
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I believe in a normally aspirated motor, you technically get the most power out of the lowest octane fuel you can burn... The higher the octane, the harder it is to combust, the lower the power-potential...
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Cool little read...
http://www.rc51.org/fuel.htm (http://www.rc51.org/fuel.htm)
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octane booster is a BAD idea.
Cleaning a carb its one of easiest tasks on the bike. take it off, take off the bowl, carefully remove the float and fuel valve, spray liberally with carb or contact cleaner, use a small nylon or brass brush to clean the bowl, remove the jets, spray cleaner through them if the y are really bad, I've had luck with CLR full strenght to remove lime deposits, and if the pilots clogged a piece of wire out of the brass brush will usually clear it out.
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I believe in a normally aspirated motor, you technically get the most power out of the lowest octane fuel you can burn... The higher the octane, the harder it is to combust, the lower the power-potential...
I believe this may be true with 4 stokes but not with 2. Unless your compression is way high a 4 stroke doesnt benifit from the higher octane
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octane booster is a BAD idea.
Cleaning a carb its one of easiest tasks on the bike. take it off, take off the bowl, carefully remove the float and fuel valve, spray liberally with carb or contact cleaner, use a small nylon or brass brush to clean the bowl, remove the jets, spray cleaner through them if the y are really bad, I've had luck with CLR full strenght to remove lime deposits, and if the pilots clogged a piece of wire out of the brass brush will usually clear it out.
If it was so easy then why did it take over one line to give a broad explanation of what to do? :P
Why is octane booster bad?
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If you are going to use race fuel you will need to richen up the main.
It burns differently.
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Why is octane booster bad?
Because you only have to think about what octane does in the fuel to get the picture. In the internal combustion engine (2 or 4 stroke), fuel is mixed with air and COMPRESSED in the cylinder (exhaust ports closed, piston climbs). This compression causes HEAT and the heat can cause the fuel to ignite when we don't want it to (before the spark plug fires). This is called DETONATION or sometimes referred to as pinging or dieseling. To prevent premature detonation (he he he), the chemical Octane is added to the fuel to enable the mixture to compress further and allow the spark plug to ignite the fuel, not the heat from the compression (detonation). Octane is used TO PREVENT THE FUEL FROM BURNING.
Engine builders design the pistons, cylinders and heads for a specific amount of compression because the bigger the explosion, the faster the engine turns. That in turn determines how much octane is required. Let's assume your stock manufactured YZ requires 93 octane. Run not enough, say 87, and you have detonation and a short lived motor. Run too much and your fuel doesn't burn efficiently, robbing you of power and sending unburnt fuel out the exhaust. Truth is, you are better running the LOWER grade fuel if you can get away with it. However, detonation is a VERY BAD THING. It is a violent explosion within the engine that can cause grave damage. Picture this:
The motor is happily spinning along, piston rises and compresses the fuel. As the rod rolls over the top of the crank and begins its journey down and around again, there is a pop and the top of the piston is gently pushed down again, helping it along. Then on the up stroke, before the rod reaches its zenith, BANG! The heat in the cylinder has detonated the fuel/air mixture and an explosion occurs. Unfortunately, everything in the engine is pushing against that explosion at that very moment. Something has to give, usually the top of the piston, but occasionally the rod.
Look at it another way: You are pushing a child on a swing set. Back and forth, higher and higher. Right at the peak, you push again, timing it just right for the least amount of effort. But then, you get an evil grin on your face and you step closer and put your hands out and push before the swinger has made it to the top of the swing. The instant jarring, stopping and change of direction makes the child cry. You mean jerk. You made the kid cry!
My final analogy for the day. Think of gasoline (Heptane, additives, and Octane) as a Margarita (Tequila, Triple Sec, lime juice). Too much Tequila and you get fired up too early. Too much lime juice and you pee a lot.
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A few things to clear up about deto.
Detonation and pre-ignition are 2 different things(only slightly though) pre-ignition is defined as occuring before the spark event and detonation occuring after the spark event.
The ignition timing is set to say 21deg BTDC so there is a very big 'explosion' before the piston gets to TDC, little extra ones won't make much difference.
Detonation is defined as uncontroled thermal runaway of end gases.
What makes the difference is both pre-ignition and detonation send out shock waves that shock waves collide with the advancing flame front from the spark event. That is what makes pock marks on the piston. Detonation can be heard from a experienced ear or with a sensor developed by those clever bods at HRC who could isolate the 'ring' frequency of detonation and make a under plug peizo sensor to detect it.The 'safe' detonation limit is 3-5 dets per kilometer for a 54mm bore.
Fuel per se does not make a difference, what does is tuning for it. All the go fast bits won't be as good as a stocker tune to the eyeballs.
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I think you just made my day VintageBlueSmoke! That was funny as hell. So I just need to find what my piston/cylinder is set for and start running that?
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EXACTILY!
But you also have to consider QUALITY. Gas from SAMS CLUB is usually bad. I don't know this for a fact but what I think happens is budget/discount gas stations buy OLD gas and then turn it over to people who are willing to skimp on quality for price. You larger operators usually gave a better quality but you pay more. The one thing about race gas is you can usually be assured of the quality!
Finally, all race bikes (that I know of) are running high compression to get the horsepower. Your XR may run good on regular but your CR (and CRF) probably won't.
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I have a 2006 YZ250 and have been riding it for a couple months. It seems to run well, but I am coming from 3 previous 4 stroke bikes so I am not well versed in 2 stroke performance.
Two other riders that I know that have quite a bit more knowledge than me on 2 strokes say that they went through pistons within 5 hours on their YZ250's because they weren't running high enough octane fuel (race fuel). They both said they ran premium but recommended that if I continue to ride/race my YZ that I run race fuel, or at a minimum blend it with premium gasoline.
This seems like a huge distraction for me as race fuel isn't immediately available, not to mention expensive.
Maybe some background is helpful; I ride 2 -3 days a week all MX tracks. I race monthly in C and Vet classes, so nothing too fast, but still competitive. I am mechanically inclined, I rebuilt the top ends' of my 4 strokes in the past and am not afraid of rebuilding my 2 stroke now.
The bike runs well, the spark plug tells me the jetting is reasonable. I currently use Sunoco 93 octane with 32:1 S2 oil. I haven't pulled the head to look at the piston, but plan on doing that in the near future. I do however notice some odd sounds from my YZ but because I am not used to 2 strokes they may be normal. I cannot tell if it is detonation or just "2 stroke rattle".
Any advice?
>:-D yes I have seen 2 bikes blow up on pump gas because of the detonation issues one 04 cr250 and a kx125 so def make the investment now rather than late
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If race fuel is not available in your area you can run 100LL from you local airport.
I run it in my YZ and it's about 5.80$ gal
no pinging here..
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If race fuel is not available in your area you can run 100LL from you local airport.
I run it in my YZ and it's about 5.80$ gal
no pinging here..
Yes you could try...
But over here, in my area, the airports do not sell AVGAS to private consumers anymore... :(
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Wysguy I remember your thread about a cr125, it was funny as hell. You had a bunch of Wisconsin used phrases and words. Anyway if your in the Green Bay area, on north broadway and Mather st. they have 110 octain leaded at the pump, Renagade is the fuels name, they used to have cam2 there. Another spot is by maplewood meats on hwy 29 west of G.B. turbo blue is sold at that station at the pump. There,s a VP dealer on velp ave. in G.B., don,t have an address tho, the boys at Team 2 racing know tho.