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Why you're running lean! New/diff. fuel answers

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Unread 3-27-2005, 11:01 PM   #1
Pinblaster
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Why you're running lean! New/diff. fuel answers

One thing many ppl don't really think about is their fuel when they get a fresh jug or change brands. I have seen many post about Nitro engines running lean as all-get-out, when they change fuels or buy a new jug of the same brand they have been running all along. Many ppl say one jug is different from the other, even if its from the same brand.

You have to keep in mind that the fuel you are running has Methanol (alcohol blend) and Nitromethane. Both have evaporative properties, which means every time you open your jug of fuel, part of the volatile chemical vapors escape and the percent of nitro, if you are running 20%, becomes around 18% or less and the fuel becomes weaker, by the time you get to the bottem of the jug. So as the Nitro content is depleted, you lean out your carb to get the same proformance out of the fuel. When you get a fresh jug of fuel you are back to 20% (full strength) and all of a sudden your temps go sky high. Therefor you must always retune your carb when you get new fuel or change brands.

The older your fuel is the weaker its going to be, the more air space you have in the jug, the more room the Nitro and methanol has to vaporize and those gasses will escape when you open the jug.

Remember: High nitro-Richer carb settings, Low Nitro-Leaner setting.

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Unread 3-27-2005, 11:08 PM   #2
psunitro
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Not sure how much nitro(meth) you are actually losing at the "bottom of the jug". It is something to think about, but there are MANY different reasons your tune can change and this may be just one of many. ALWAYS retune if changing brands and nitro %.

And the more nitro=richer and less nitro=leaner.........really not true. All depends on the brand and oil content.

Last edited by psunitro; 3-27-2005 at 11:10 PM.
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Unread 3-27-2005, 11:15 PM   #3
4u2nv
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From now on, Im vacume sealing my jugs..hehe ::Jk::
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Unread 3-28-2005, 1:18 PM   #4
rocknbil
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If you look at the following MSDS sheets

Methanol
Nitromethane

You'll see the vapor density of Methanol is 1.1 (with air being 1) and the evaporation rate is a whopping 5.2 (with the ether benchmark as 1,) while nitromethane is has a vapor density of 2.1 and an evaporation rate of 1.39.

This is further complicated by the fact that nitro FUEL is mixed with synthetic and natural oils.

What this means is the nitro really is no more evaporative than water, but the alcohol IS. Even at 5.2 it doesn't evaporate nearly as fast as you'd think - it's only evaporating from the surface exposed to air. If you squeeze the air out of your container, you'll never see a difference. Fuel will go bad from water contamination due to the hygroscopic qualities of methanol long before it will evaporate to the point of changing your mix percentage.
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