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Biggest factor of fuel/oil that affects jetting
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[QUOTE="Rich Rohrich, post: 1471010, member: 16241"] I think what you're doing is interesting. That said, I also think you'll have an incredibly tough time proving any sort of cause and effect correlation between a standalone viscosity test of oil and a repeatable impact on the fuel curve. I know you understand all of the stuff below but for the folks who may not have dug as deep into the subject of jetting it might be useful to remember a few things about jets, jetting and the ultimate goal air/fuel ratio in general. Mikuni hex head jets are numbered by bulk flow, while Mikuni round head jets and Keihn jets are numbered by inner diameter in mm. The flow difference between a Mikuni 175 hex jet and a 180 is about 6cc ~3%) . Keihn jets are numbered by jet id, and the difference between a 178 and a 180 is about .0008" (I'll let those so inclined do the math to determine the flow difference) . Now to further confuse the issue and to get more to the point of how oil might impact "jet flow" keep in mind that air/fuel ratio is based on weight of fuel and weight of air, but jets essentially meter by volume. So we really need to know the weight of the fuel flowing through a jet to understand all this. In simplest terms fuel weight is a function of the area of the jet multiplied by the value of the square root of the fuel head pressure multiplied by the density of the fuel. It looks like this: weight of fuel = jet area * ( SQR Root (head pressure * fuel density) None of the above takes into consideration the changes in fuel vaporization characteristics as you change altitude, which can have a profound impact on the final air/fuel ratio available in the combustion chamber ( the only place a/f ratio is really significant anyway) when the sparkplug fires. As fun as it might be to look at jetting this way, the sad fact is the cross sectional area of two jets marked with the same number can vary FAR MORE than the difference in flow due to small changes in density . Good jets can vary as much as 5% cheap jets can be closer to 10% variance. So I have no doubt you can find some specific differences in "bulk flow" through a jet based on the true viscosity of an oil. How that will ultimately relate to a change in the "usable" (and the word USABLE is critical in this case) fuel mass that the engine sees in the combustion chamber is likely to be open to debate. Please don't read this as criticism, I'm interested in hearing more about what you ultimately find. [/QUOTE]
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Biggest factor of fuel/oil that affects jetting
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