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Discussion Starter #1
I want to run some race fuel in my hopped up XR to see how it will run out. i went by a dealer and a guy there recommended "Ultimate 4" by VP. He said it was specially formulated for single cylinder 4 strokes.

Anyone used it or like something else?
 

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Ultimate 4 or U4 is a highly oxygenated fuel that is unleaded that most of the pro motocross guys run since the new fuel restictions. Do not spill it because you will be high on the fumes quick. I had a leacky gas cap once while racing motocross and that stuff splashing up in my face and on my gear. I had the worst headache and I was so dizzy that I couldn't ride my second moto. I forget what the octane is though, something like 98. If your xr has pretty high compression I would run some vp c12 to make use of the lead and the octane.
 

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05mxdiesel said:
Ultimate 4 or U4 is a highly oxygenated fuel that is unleaded that most of the pro motocross guys run since the new fuel restictions. Do not spill it because you will be high on the fumes quick. I had a leacky gas cap once while racing motocross and that stuff splashing up in my face and on my gear. I had the worst headache and I was so dizzy that I couldn't ride my second moto. I forget what the octane is though, something like 98. If your xr has pretty high compression I would run some vp c12 to make use of the lead and the octane.
U4 is leaded 92 octane. Very distinct smell (I love the smell - from a distance. Up close it's like Ron said.. wooozy). We run C12 50/50 in our crf450R.

I wouldn't suggest running U4 unless you're just looking to try it to see what kind of kick you can get from race gas. You may pull 3-4hp off U4 alone (wonder why it's so popular?), it's so oxygenated. But you also should shut off your petcock & drain your carb (run it dry?), afterwards, it's highly corrosive. I think C12 is 108 octane (leaded).
 

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Discussion Starter #6
it is a 400 that has been bored out to 426....high comp piston....barnums custom cam...springs..pumper carb...barnums headed and exhaust..yada yada....

i am just looking for a kick...if i take it out to a track for some laps.
 

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U4 is for 4 strokes period not just singles. Other brands make equal or better fuel such as the Sunoco MO2X. It makes equal to more HP then the MR-9 by VP but at way cheeper prices. MR-9 and MO2X both make more power then the U4.

U4 is not used by any Pro Motocross/supercross teams as it is illegal. U4 is illegal in all AMA pro forms of racing. MR-9 and MO2X are legal in Roadracing. And MO2X is legal in Motocross and Supercross. Supercross and Motocross pro racing has a special blend of VP fuel but the name escapes me right now.

U4 is oxygenated and leaded as is MO2X and MR-9
If you run the U4 you will need to drain your tank and run a little pump gas through it before you let it sit longer then say 2 weeks. U4 will gel up and clog your carb.

MO2X you can leave in your bike and it will not gel.

Also MO2X is 115 octane so it would run great in your XR. Anything with 12:1 compression or higher will run good on high octane/oxygenated fuel.

Hope this helps, If you have any more questions pm me. I am in the race fuel biz for Sunoco if you cant tell and want to help any way I can

Ryan
 

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I ran both the U4 and VP 112 in the XR, and for the money, go with the 112. U4 cost 3-4 times as much as the VP, (neat stuff though). Be warned though, with race gas in that bike, when you're in 3rd gear it'll act like its in 1st. :thumbup:
 

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Do you guys know why U4 gels up?

I dont run it cause im on a yz250 but love to learn!!!

I only run 50/50 c12 when at the dunes but would love to understand the corrosive nature of this fuel.
 

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I've run U4 (straight, not mixed with reg. gas) for the last couple years. I do not drain my tank, nor do I drain my carb after use. The gas has not gelled up or caused any damage in either my old 03 YZ450 or my 06 YZ450. Sometimes the bike will sit for a month. Maybe I'm just lucky? Maybe it's the air in SoCal?

U4 is nice stuff and I can get it at my local Cycle Gear.
 

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The reason it gels has something to do with the chemials they use. Remember these hi performance fuels are 90-95% synthetic.

A month is about the longest you want to let it sit. Before I got hooked up with Sunoco I ran U4 in my road race bike and raced once a month with no problems for a while then all of a sudden started having carb problems. Took apart the carb and had a bunch of green gunk in it. Cleaned everything out and it was A ok again. I would be if you took apart the carb you would find green slug.

Best of luck
Ryan
 

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I love the smell of that stuff. I sugested they make a cologne out of it until I realized you'de most likely just have a bunch of fat Harley guys chasing you around......
 

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100 octane racing gasoline available from the pump at the Shell station. $4.99 a gallon. Works great, no goo or corrosion. Bought 10 gallons when I was in Daytona. When that runs out, a local station has 110 octane racing gas, $4.99 a gallon. Not jet feul....racing gas. Look around. Bet you got a station close by that sells it.
 

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treybiker said:
I ran both the U4 and VP 112 in the XR, and for the money, go with the 112. U4 cost 3-4 times as much as the VP, (neat stuff though). Be warned though, with race gas in that bike, when you're in 3rd gear it'll act like its in 1st. :thumbup:

Not sure what you were meaning, but U4 (Ultimate 4) IS a VP gas..
Its not that it is corrosive, it is that the Oxygenate will evaporate and leave a gummy residue behind if left in the carb (or injectors/electric fuel pump on roadrace bikes) for more than a few weeks. Just take the fuel line off the carb and drain..chase with some pump gas and run the bike a bit. Easy..
 

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any of the oxygenated race fuels especially U4 to get the most out of them you need to richen your jetting. I sell U4 and haven't had any customers complain about it jelling up, but VP started putting warning labels on it not to leave it in our bike for extended time. For the Sunoco guy have you done back to back dyno runs of M02x vs U4 under the same conditions ? I have run Mr9 and U4 back to back and they are about the same if mapped properly the difference is MR9 doesn't require the bike to be richened up from pump gas like the U4 does. Yes U4 is 92 motor octane which is the number that is important for race bikes unlike the m+r/2 that sunoco uses like pump gas. using the same method U4 would be close to 100 octane. They also make U2 which is a higher octane version of the same fuel for the same price. Look around the AMA pro races and you will see almost all of the factory teams VP-that should tell you something about the quality of the fuel.
 
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