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Enduro Intake/Carburetion - 2 stroke Jetting, Reeds, Air Filters, etc. |
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#21
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I'm going to get into the carb this weekend and see what's what - been putting it off and need to do it anyway. I think an interesting test would be to try 60:1 and see if there's any noticeable difference - might do that too on the next ride. Thanks for all the responses gents |
#22
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Material properties of miscible fluids are typically additive. In the same way that density was additive for the previous example. Gasoline isn't particularly viscous around 0.4-0.7 cSt at 40C, infact its generally less viscous than water. Where as 2 stroke oils are around 45 cSt at 40C. So the difference in viscosity is about 90 times in favour of the oil. Lets consider a mix of 50:1, or 2% 0.98x0.4 + 0.02x45 = 1.29 cSt, so you've tripled your viscosity by adding 2% oil. As for your previous comment on the reduction in octane by adding oil, that is again due to the additive nature of miscible fluids, the gasoline has a octane number of say 90. The oil has a much much lower one, probably zero, but lets say 4 for the sake of the example. So when you mix at 2%, 0.98x90 + 0.02x4 = 88.3. So by mixing at 2% you have reduced the octane rating by ~2 points. Thats why you will have read about reduced octane ratings in premix. |
#23
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I was thinking that a more viscous fuel would require a higher amount of airflow to be drawn through the carb, resulting in a leaner condition.
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#24
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I run Amsoil Dominator (not Interceptor) at 50:1 with no spooge but I'm also using a Leo Vince with spark arrestor. I believe Interceptor has a higher flash point than the Dominator, that coupled with the Q could be your issue.
BUT I agree if throttle response is good then carry a paper towel and wipe the sponge on occasion.
__________________
Fred Overstreet 2010 EC250 SixDays 2004 GasGas EC300 -Sold to a good home 2006 GasGas EC250-Sold to a good home 2006 GasGas TXT 280 Pro |
#25
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Correct Oil ratio
This is getting pretty deep into the science. My opinion on this is not to run higher than 50:1 oil ratios. You will give up engine life with mixtures higher than this. When testing outboards with variable injection, the engine can tolerate leaner oil mixtures (up to 100:1) but it will require richer mixtures (40~50:1) to maintain proper lubrication to critical parts of the engine. Since we are running premix on our GasGas I would recommend staying with 50:1. Once this is defined you can focus on the correct carburetor setting to optimize performance.
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#26
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When I have time this weekend, I'm going to pull the carb and check the jetting....need a base line |
#27
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Wait: I'm confused...
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You assumed an octane rating of 4 (perhaps as low as zero) for the oil: wouldn't that low of a rating indicate a dangerous propensity to spontaneously combust? I apologize to all for hijacking the thread earlier. Cudos to fred, mjtursky, and livtoday for helping to get us back on topic. Having said that, I still appreciate noobi's willingness to explain things. Though I have a hard time following the science, I find it absolutely fascinating. Thanks.
__________________
Newest Spanish Girlfriend: 2011 300 Six Days My Daughter is a U.S. Marine |
#28
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My 2012 has no spooge problems and I am using GRO at 50:1.
I have the bike jetted slightly rich (safety), and have great throttle response everywhere. Cheers Mark
__________________
Xr 250 ( first bike) 98 Rmx 2007 Gas gas 300(swapped for trials bike) 2008 280 Raga replica 2012 Gas gas ec 300 E |
#29
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Actually Domiminator has the higher flashpoint but the difference is very small and both are on the lower end of the flashpoint spectrum of the top synthetic oils. I have never ran better oils, yes there are some that are just as good but none (here in the U.S.) can I get as cheap as Amsoil.
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#30
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You've kind of jumped the gun a bit by saying octane is a resistance to combustion, although that's an effect of higher octane numbers. Its a reference to the activation energy of the combustion reaction that must be overcome by work done on the mixture. Work is done on the mixture by compression, it loosely obeys PV=nRT, and as volume decreases pressure increases, but temperature also increases. A lower octane number mixture requires less work to be done, so the activation energy is overcome at a lower pressure than a higher octane mixture. Hence the resistance to combustion. Now when the spark goes off, there is a localised hot spot where the spark has arced, and that is what overcomes the activation energy and causes combustion. Now oil doesn't combust under compression alone, so an octane number doesn't apply. So when you dilute the gasoline with oil, the overall mixture volume has a lower octane number because the oil doesn't contribute to it. Also, flash point does not mean ignition, specifically it means the point at which it becomes a combustible vapour. So an oil still requires an ignition source once in a vapour state. Gasoline doesn't necessarily. As for viscosity increases, I would say it is possible that you could have a reduced flow through the jets if the viscosity was increased by a large enough amount. I feel that that would be incredibly difficult to model. Hope that helped a bit. Last edited by noobi; 01-10-2014 at 09:12 PM. |
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