Gelling of the ultimate 4 race fuel

[racer8]

Anyone having the problem of the u-4 face fuel gumming up in the carb.

I drain my float bowl overnight and still upon riding the next day, my throttle slider is slow to return to the idle position.

Thinking of mixing it 50/50 with another race fuel.

The u-4 is known for doing this, just wonder if anyone had any ideas.

I have 5 gallons I just purchased.

And looking for a fix.

Thanks

[KJ790]

I have heard horror stories about U4 gumming, but I ran it for years in my bikes and didn't even drain the carbs and never had a problem. I would let my 250F sit for a week with U4 in it and never had any problems. Then NY outlawed MTBE, so VP racing came out with U4E, which I ran for a full season with no problems. This year VP came out with U4.1, which was advertised as not having the gumming problems of U4. I figured why not try it. So I threw some in and my bike ran fine. Went to ride the next day and the carb was plugged solid. I took it all apart and cleaned everything and tried it again, this time I drained the carb after riding. Again, the carb was plugged solid. I actually had to use pliers to pull the needle valve out of the seat. I called VP and asked what could cause this and the guy on the phone kept telling me it was impossible and I was making it up. Then he tried to tell me that my story was BS b/c it would be impossible for my bike to even run with the jetting I had in it (which was just a tad richer than stock on the pilot and main, just like everyone else runs). Needless to say, VP has lost a customer.

[Ga426owner]

U4 is not the current VP available Fuel anymore. When it was available, it clearly was labeled telling users tro drain the carb after each use.

If you have just bought U4 it has been discontinued for almost 10mos and you should return it. It did gum up carbs as I found out even after draining it every time.

U4.1 was the next revision....that only lasted a short while...up to the 2007 Daytona 200 - when bikes using it blew up....it was discontinued and now the replacement fuel is U4.2. This fuel is much better at not gumming up a carb, but I still drain it after each use regardless. It also does not smell up the entire shop or house anymore. It does however work very well at adding power to any stock 4stroke motor. And it does cost $$$$. Never dilute U4 you ruin the oxygenation factor of the fuel. You can mix C12 if you prefer

[racer8]

So you are saying that I can mix it with the c-12?

Or that c-12 alone can be mixxed?

Thx.

[Ga426owner]

is it U4 or U4.1/U4.2?

Did you just open the sealed 5gal tank or has it been open to air for some time? If it is fresh use it straight and no premix. Drain after each use.

[TeamPrecisionIT]

Stop being cheap and buy MR9/10!

[racer8]

It is the u4...

I had the shop put 5 gals in my plastic fuel jug,who knows how long its been in thier drum!

I`am just looking at mixing it 50/50 with the ms103 fuel to delute the gumming additive.

Looks like the way to go is with the all n ew u4.2 fuel.

Hows that idea sound????More excuse to go riding and burn up the 10 gal of fuel......saweeeeeeet!!!!!

[djtroy]

I use 4.2 and its great

[jeffboyd47m]

I bought and ran U4.2 at the Mammoth MX this year. It ran real well at the high altitude but was difficult to start my bike when it was hot. I asked the VP guy about the problem and was told that the gas had a lower boiling point and was getting too hot in the float bowl while the bike was hot and not running. Once I ran all of the fuel that I purchased, I went back to pump gas and have not had the problem since. I won`t be buying anymore.

[KJ790]

I got a question why we are on this subject. I have zero experience with race fuel in a Mx bike. All streetbikes here. Anyways is there a huge advantage to it or any? Second say I just wanna run race fuel on race days, Does it affect jetting etc? Last but not least is it any harm to your motor in running race fuel?

There are different types of race fuels. A high octane fuel is needed on engines with high compression ratios to eliminate detonation (mainly modified two strokes). Four stroke motocross bikes do not need high octane, 93 pump gas is all that is needed unless your bike is highly modified. Oxygenated race fuel (such as U4, U4.1, and U4.2) gives more power. These fuels are about 98 octane so they are not super high octane, but they have high oxygen levels. These fuels are illegal in AMA pro racing, but are legal in amateur racing. They give the bike a slight increase in power, as well as making it run crisper. These fuels also smell amazing, but will put you back about $13.50 a gallon. You do have to jet a little richer with oxygenated race fuels.

[racer8]

$10.99 per gal.....175 main jet. Eng is highly ported and modded.

Spoke with VP tech,He said to go and mix a 50/50 or less mixture will be fine.

Then use thier u4.2

Thanks for all the help guys!!!!

[PatrickM]

I use a 50/50 mix of C12 and Shell 91 V-power pumped gas. It runs very well and my bike starts very easy. the only problem is that I see my bike eat more gas than when i ran it on staight pumped gas. The crisper throttle response is worth its weight in gold.

Patrick M.

[Ga426owner]

Stop being cheap and buy MR9/10!

yea it is only 20.00-30.00 a gal....?

[Ga426owner]

I got a question why we are on this subject. I have zero experience with race fuel in a Mx bike. All streetbikes here. Anyways is there a huge advantage to it or any? Second say I just wanna run race fuel on race days, Does it affect jetting etc? Last but not least is it any harm to your motor in running race fuel?

Matt,

power is increased up to 3hp....that is why I use it. and you can definitely tell.

I run nothing but race fuel all the time...I am spoiled and used to the way my bike runs with it...Straight U4.2 or C12 mixed with pump prem gas 50/50

You must jet for it...typically 1 step richer for U4.2

Motor runs much better with it,...it burns cleaner and adds the power

I always drain my carb clean and dry after each days riding with any race fuel

[Kent Rathgeber]

Matt,

power is increased up to 3hp....that is why I use it. and you can definitely tell.

I run nothing but race fuel all the time...I am spoiled and used to the way my bike runs with it...Straight U4.2 or C12 mixed with pump prem gas 50/50

You must jet for it...typically 1 step richer for U4.2

Motor runs much better with it,...it burns cleaner and adds the power

I always drain my carb clean and dry after each days riding with any race fuel

You mix your C12 race fuel 50/50 with pump premium?? I was always told NOT to because I'm just diluting the race fuel.

I run straight VP 4.2 when racing (pump premium when practicing, cause I'm too cheap to practice with race fuel:busted: ) in my 07 YZ450F, but not for the reasons you might think. I run it because the bike starts easier if I stall in a corner, or wherever. I don't run it for the extra power I get or the easier jetting (I just move the fuel screw based on temps. I still have stock jetting in my YZ-F otherwise). I also have no problems with VP U4.2 gumming up the carb.

[Ga426owner]

You mix your C12 race fuel 50/50 with pump premium?? I was always told NOT to because I'm just diluting the race fuel.

I run straight VP 4.2 when racing (pump premium when practicing, cause I'm too cheap to practice with race fuel:busted: ) in my 07 YZ450F, but not for the reasons you might think. I run it because the bike starts easier if I stall in a corner, or wherever. I don't run it for the extra power I get or the easier jetting (I just move the fuel screw based on temps. I still have stock jetting in my YZ-F otherwise). I also have no problems with VP U4.2 gumming up the carb.

yes I mixed C12 for a 4stroke. This was recommended to me by the good folks at ZipTy Racing as this is what they told me the race team uses. This was after I got a bad batch of U4 and it really messed both of my carbs up. In a 2stroke I would run it unmixed. Now that all of the C12 is used that I bought, I use U4.2 straight.