Jetting for MR2 over C12???
- Thread starter elvismx
- Start date
murphy's law
Member
- Oct 11, 2002
- 47
- 0
elvis,
i was running c-12 in my 02 cr-250 and found that i had to run a smaller main in the summer to keep it from drowning in fuel. (#370 --stock is #380) i couldnt figure this out because i assumed that c-12 ran leaner than pump fuel. i was wrong. during really hot days i found that if i mixed c-12 50/50 with mr-2 it really cleaned up my jetting so it was spot on. a couple of experts recomended this to me and it worked pretty well. another writer in this forum re-affirmed this when he said that he would ran straight c-12 in the morning moto when it was cool and then added mr-2 as the temp grew warmer to avoid having to pull his carb off and make jetting changes.
i was running c-12 in my 02 cr-250 and found that i had to run a smaller main in the summer to keep it from drowning in fuel. (#370 --stock is #380) i couldnt figure this out because i assumed that c-12 ran leaner than pump fuel. i was wrong. during really hot days i found that if i mixed c-12 50/50 with mr-2 it really cleaned up my jetting so it was spot on. a couple of experts recomended this to me and it worked pretty well. another writer in this forum re-affirmed this when he said that he would ran straight c-12 in the morning moto when it was cool and then added mr-2 as the temp grew warmer to avoid having to pull his carb off and make jetting changes.
According to MXA PC runs MR2 in their race bikes. C12 is higher on the motor octane scale where MR2 is closer to premium pump. MR2 is oxygenated and costs bucks. MR2 will most likely require richer jetting because of the oxygen. VP has a new fuel called Power Four which is also oxygenated and has a lower motor octane than C12 and supposedly has had good results. I may test it soon. Compare your compression ratio to the motor index of the fuels. The closer the motor octane matches your compression the more efficient will be the energy output. I have also read that mixing the 2 fuels compromises the individual fuel performance, probably because the blend is altering the motor octane value. Race fuel should be more consistent than pump because pump is handled a lot. Buying in a sealed 5 gallon can insures integrity. What kind of plug read are you getting?
What on EARTH is that supposed to mean?
Low compression 9.5:1 engines don't need 112 motor octane anti knock. It has never worked for me. For example VP Motorsport 103 is recommended for engines at 11:1 according to my dealer. Ultimate Four has 92.2 motor octane which is what they recommed for my 9.5:1 engine. Are they BSing me?
Fuel recommendations based purely on octane numbers ignore far too many important fuel parameters to be of ANY value. Static (mechanical) compression ratios are useless without considering the Intake Valve Close timing, combustion chamber design and host of other factors. As an example YZ444Fs can easily run 14:1 CR on pump premium without knocking, and 250Fs can do likewise if they are set up correctly, while lots of air cooled engines get into trouble at anything over 9.5:1 on pump premium.
Lots of people selling fuel don't have the first clue about combustion, or fuel chemistry so their advice might not always be valid.
Back to the original question.
Whether or not MR2 will be picky is really an engine issue. Engines that scavenge well, tend to be very tolerant, engines with poor transfers are much tougher to deal with.
If you are currently running straight C12 and have it jetted really SHARP then I would personally bump the main 3-4 steps to play safe. The pilot will probably need a bump and the needle can usually be adjusted within it's range. If you are switching over from pump fuel the changes will be much smaller, and MAY even require you to LEAN the jetting when going to MR2.
Lots of people selling fuel don't have the first clue about combustion, or fuel chemistry so their advice might not always be valid.
Back to the original question.
Whether or not MR2 will be picky is really an engine issue. Engines that scavenge well, tend to be very tolerant, engines with poor transfers are much tougher to deal with.
If you are currently running straight C12 and have it jetted really SHARP then I would personally bump the main 3-4 steps to play safe. The pilot will probably need a bump and the needle can usually be adjusted within it's range. If you are switching over from pump fuel the changes will be much smaller, and MAY even require you to LEAN the jetting when going to MR2.
Last edited:
- Jan 25, 2000
- 1,823
- 0
I've been splashing some C12 in with pump gas for my '03 KX125 to improve detonation resistance, but MR2 seems the better choice, since the KX is a rich running bike that's tough to jet out properly. Oxygenated fuel may be the way to go on some tempermental 125's - another experiment is waiting. :thumb:
My 426 doesn't seem to care what kind of fuel it gets, yet our mildly tuned DS80 that barely pumps out 6 hp is more prone to detonation than any bike I've owned, so it's not necessarily a performance or compression issue when considering race gas. Engine design has a big influence on it's fuel requirements.
My 426 doesn't seem to care what kind of fuel it gets, yet our mildly tuned DS80 that barely pumps out 6 hp is more prone to detonation than any bike I've owned, so it's not necessarily a performance or compression issue when considering race gas. Engine design has a big influence on it's fuel requirements.
bclapham
LIFETIME SPONSOR
- Nov 5, 2001
- 4,340
- 0
Hey Ron...let me know when you want to take a sip out of the brown bottle! that said, i think Rich will tell you that mixing oxy race gas with pump is an even worse idea than mixing c-12 with pump! if you think this route will clean up the spooge, it wont help that much since ive tried, and i but still get spooge even after jetting to the point of bogging and/or detonation! but it has been a bit of a makeshift stopgap for me after i sussed it out....
Just out of interest, how much are you paying for C12? with my entraprenurial(sp?) spirit, i am thinking of buying a 55gal drum of C12 and selling some 5gal lots to my friends so we can get a good deal.....i can get loads of new drums (used once) from work and seal them up so let me know if you are interested
Just out of interest, how much are you paying for C12? with my entraprenurial(sp?) spirit, i am thinking of buying a 55gal drum of C12 and selling some 5gal lots to my friends so we can get a good deal.....i can get loads of new drums (used once) from work and seal them up so let me know if you are interested
- Jan 25, 2000
- 1,823
- 0
I don't remember how much I paid for C12 exactly - 30+ bucks for sure. Mixing C12 with pump is certainly better than running straight pump, but whether it's an efficient use of the fuel is in question. I'm aware that mixing two fuels will not result in a proportional octane number (i.e. mixing half 90 octane and half 100 octane will not very likely result in 95 octane, because combining the fuels is not that predictable). Never the less, that's the route I choose to take. Purists would balk at the idea of combining race gas with pump swill. If I ever learn how to corner fast, I'll run straight race gas (I promise).
Right now, I find the spooge level acceptable. If I putt around too much, then it becomes noticable, but 125 MXr's are not made to lug around on. Let me know what kind of deal you can get. :thumb:
Right now, I find the spooge level acceptable. If I putt around too much, then it becomes noticable, but 125 MXr's are not made to lug around on. Let me know what kind of deal you can get. :thumb:
MR2 IS a VP product. Here's the latest list of leaded fuels from VP.
http://www.vpracingfuels.com/vp_01_fuels.html?mgiToken=D031D80210240E8B415#leaded
- Jan 25, 2000
- 1,823
- 0
Rich, you beat me to it - I just visited the VP site and realized my error. That's what I get for listening to the parts counter guy :confused:. Now I'll have to find the closest local supplier. This may be the best fuel for tempermental 125's, but I'll have to try it before I come to any conclusions.
DOOOH . That's ALWAYS a treacherous path to take. :scream:
Personally I've found oxygenated fuels to be MOST useful on small bore two-strokes so I think you'll be pleased once you tune for the fuel. It's great bang for the buck and will allow you to tune really close to the edge without hurting the engine. It's amazing how much you can wake up a two-stroke with seriously aggressive tuning. Most guys that are satisfied with bolting on a poorly matched pipe and running ultra-conservative jetting (i.e. hopelessly RICH) will never know what they are missing. :thumb:
