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ttr250dude

Why is race gas prone to stalling?

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I used to run 100% leaded 110 Sunoco in my bike and it stalled like a mofo, it would die literally every 1/4 mile in technical single track. I now use 100% pump fuel and it lugs through low rpm like a tractor and never stalls. Why is that?

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Hmm... Thats a good question. I dont think it has anything to do with race gas. If it did its because the race gas is harder to ignite.

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I used to run 100% leaded 110 Sunoco in my bike and it stalled like a mofo, it would die literally every 1/4 mile in technical single track. I now use 100% pump fuel and it lugs through low rpm like a tractor and never stalls. Why is that?
Sunoco 110 is a fairly low quality pump "super premium" and gets the extra octane by less expensive chemical means that end up with the fuel needing extra heat to make it ignite. It's somewhat like the summer blend gasolines used in a lot of places around the country.

Normally, with a high quality fuel that has more octane than the engine needs, there is no penalty in power or performance, only in the fact that you're wasting your money buying it. But with a lot of the cheap stuff, you start hearing complaints about hard cold starting and frequent stalling at low speeds when you don't have any real need for that much octane.

Real race fuels can provide additional power because their chemical blend has more energy potential, not because they have a higher octane rating. Octane is resistance to detonation, and nothing else. If pump premium doesn't ping, you don't need any more.

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I used to run 100% leaded 110 Sunoco in my bike and it stalled like a mofo, it would die literally every 1/4 mile in technical single track. I now use 100% pump fuel and it lugs through low rpm like a tractor and never stalls. Why is that?

To my understanding when switching from pump fuel to race fuel some jetting tweaks will be required for optimum performance. I'm NO fuel expert, however race fuel does NOT burn "quicker" race fuel burns more "complete". Race fuel actually combusts slower than pump fuel. I believe you typically need to lean out your jetting slightly to compensate for the different burn characteristics of race fuel. Maybe this had something to do with your erratic engine bahavior ?

Edited by Polar_Bus

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To my understanding when switching from pump fuel to race fuel some jetting tweaks will be required for optimum performance. I'm NO fuel expert, however race fuel does NOT burn "quicker" race fuel burns more "complete". Race fuel actually combusts slower than pump fuel. I believe you typically need to lean out your jetting slightly to compensate for the different burn characteristics of race fuel. Maybe this had something to do with your erratic low end engine bahavior ?

I've found in my 2 stroke, typically with 110 race fuel, I need to go down 2 mainjet sizes and 1-2 clips leaner on the needle.....and appropriate air screw adjustments.

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sounds like you should just stick to premium?

And if you're having a hard time spending the money elsewhere, send me a pm, my tuition could use a major sponsor!

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To my understanding when switching from pump fuel to race fuel some jetting tweaks will be required for optimum performance.

Race fuel actually combusts slower than pump fuel.

I believe you typically need to lean out your jetting slightly to compensate for the different burn characteristics of race fuel.

The first statement is true, the other two aren't.

The burn speed changes very little from one fuel to another, and is not related to octane.

A number on race fuels, primarily the oxygenated fuels like the U4 family, require richer jetting to compensate for the added oxygen that gets released to the combustion process. Fuels with a high content of toluene may require richer jetting as well.

The biggest problem the OP has here is that the premise of the post is flawed; race gas is not more prone to stalling. Sunoco 110 is, however.

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Race gas isnt any harder to ignite than pump gas.

That can be your little secret.

Gray: who is right? me or him? Im 99% sure that in a post somewhere you said that high octane gas isnt any harder to ignite than pump gas.

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High octane fuels are no more difficult to ignite with a spark or flame than low octane fuels.

Cheap fuels of any octane number can be a problem.

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Cool. Where can i get vp u4.4 shipped to me at a reasonable cost? Theres a place that sells vp and sunoco fuels about 20 mins from my house. Only problem is that they won't place orders smaller than a 55 gallon drum.

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Cool. Where can i get vp u4.4 shipped to me at a reasonable cost? .

Depends on what your definition of "reasonable". Shipping costs WILL kill you. I have a few local to me race shops, and my local Haffners gas station carries CAM II. Ive used the common VP C12 as well with excellent results. Many auto race shops have 55 gallon drums of VP on hand and will sell to you by the gallon. Ask around local to you. That VP 4.4 might be difficult to get as it looks like a new AMA legal motorcycle specific only race fuel. If you want the 4.4, I believe VP sells 5, 30 and 55 gallon drums for purchase..

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IF you rejet for it, a good fuel like U4 will get you 1 or perhaps 2 extra HP in a 450.

If you end up with the final true cost of your fuel at, let's say $7/Gallon conservatively, you burn 1.5 gallon an hour, and you ride 2 hours every week, that's $1092/year. Divide that in half because normal pump premium here is around $3.50, and you have $546 for the two hp for a year. That's not too bad a deal, except I don't think you can get it that cheap, and, here's the kicker, if you stop paying for it, the power goes away. :smirk:

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Gray: i wanna make sure i got this figured out. So most race fuels will give you a couple extra hp, but the stuff i was using is such poor quality that it doesnt provide any gains and can actually create problems?

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