Race gas

So when I was at my local track recently there was a guy selling knock off VP C-12, 110, and U4.

He showed me a print out of the HP and TQ specs when they dyno'ed a few bikes to show the power gains.

He said that they had to go up 4-5 sizes in the main jets to get them to run well. They tested a few 65's, a mod 85, and a 450.

Is it normal to have to go up that many sizes when running race gas?

It seems awful dramatic to me, but then again, if I were an expert on race gas I wouldn't be posting this thread.

What have your experiences been?

It depends. 4-5 sizes would be going from a 165 to a 175-178, and that does seem a little excessive. But you can run a 4 stroke quite a lot richer than optimum and get away with it, too.

The U4 family of fuels is oxygenated, and some increase in jet size is needed just to compensate for the additional oxygen released into the combustion reaction. Some of the chemical elements of race gas, such as toluene need to be run richer to burn correctly, too.

U4 fuels will realistically add as much as 2 hp to a well tuned 450, but that's about it.

Does all race gas smell good? At my track the guys racing in the class above me are running full race gas and it smells like heaven:busted: jk. But someone told me it was U4 but im not sure...:thumbsup::worthy:

So when I was at my local track recently there was a guy selling knock off VP C-12, 110, and U4.

He showed me a print out of the HP and TQ specs when they dyno'ed a few bikes to show the power gains.

He said that they had to go up 4-5 sizes in the main jets to get them to run well. They tested a few 65's, a mod 85, and a 450.

Is it normal to have to go up that many sizes when running race gas?

It seems awful dramatic to me, but then again, if I were an expert on race gas I wouldn't be posting this thread.

What have your experiences been?

So here's my experience with U4.2 (don't run the lower version).


  1. I was told 4.2 doesn't gum up your carb (wrong, it does)

    1. It does provide increased HP (it works as claimed)
    2. It's addicting (yes, very true)
    3. It has a very strong smell (yes again)
    4. It's expensive (yes, by a lot)
    5. Are there better and more cost effective alternatives (yes)

In short, Race Gas will pep up your low to midrange by a noticeable amount. It made me smile the first time I tried it, but it's addicting and costly. However, you DO have to not only drain your tank and carb, but you also have to add pump gas and run the bike afterwards as well. If you don't, when you open your carb, you will have a blue film throughout. This is time consuming, but again, race gas does work and probably would be a welcome addition for the YZ.

For myself, I finally got to the point of trying to find a more cost-effective solution that required less maintenance (zero). I found it. A stage 1 cam. This is a 1 hr project and it's essentially a bolt on component. It runs better than race gas, IMO and you can go back to pump gas as a result. Bottom line: very impressive gains with the cam , but not a hard-core change to your top end. The cam lobes are different, but not so aggressive that you are sacrificing your engine. My bike now starts one kick as a result so there's additional benefit. :thumbsup:

In short, a Stage 1 Cam provides a much better bang for your buck with less overall hassle. Nothing to maintain. Also, running race gas, I didn't need to change my jetting at all. Maybe a few turns on the fuel screw, but it ran fine with no changes to the bike.

Hope this helps.

Rick makes an excellent point.

Set aside the annoying, but very necessary additional maintenance for a minute, and look at just the expense.

A set of cams will cost roughly $300 or less once. If you run U4.2, and you burn no more than 10 gallons a month in your bike, it will cost you $600/yr over and above your normal fuel costs for no more power gains than the cam set provides, if that much.

Rick makes an excellent point.

Set aside the annoying, but very necessary additional maintenance for a minute, and look at just the expense.

A set of cams will cost roughly $300 or less once. If you run U4.2, and you burn no more than 10 gallons a month in your bike, it will cost you $600/yr over and above your normal fuel costs for no more power gains than the cam set provides, if that much.

Since I only have one Cam on my biike, a new Hotcam cost me $200. They sell on eBay for much less actually. Surprisingly, there were are total of about 10 bolts for everything. It ended up being a very simple add-on, but the timing can be a tricky for a first-timer. Hotcams has video's on their website that I followed. Really helped.

IMHO, the power gains and torque curve was altered in a VERY positive way, better than 4.2 race gas. I can only imagine combined how the bike feels, but when 4.2 jumped an additional $12 overnight, I looked at my options. At roughly $14/gallon, the cam will have paid itself off in no time since I ride just about every weekend.

My chart looks a little different than the YZ's, but there should be good benefits regardless of brands. The YZ charts looks dated.

http://www.hotcamsinc.com/index.cfm?fuseaction=cProducts.view&productid=485

http://www.hotcamsinc.com/index.cfm?fuseaction=cProducts.list&brandid=10&modelid=35&modelyear=2007&enter.x=66&enter.y=11

The price of U4.2 and the reprocussions it has ,why would anyone put this fuel in there tank.2 horsepower is not worth it,especially on a 450,who knows what your motor picks up from using it.

The price of U4.2 and the reprocussions it has ,why would anyone put this fuel in there tank.2 horsepower is not worth it,especially on a 450,who knows what your motor picks up from using it.

Repercussions? To what?

Race Gas is better than anything you'll put in your bike using pump gas and will run cleaner.

If you need the power....oxygenated race fuels are pour in power.

All race fuels you would run burn cleaner and are overall better for you bike long term....

Question is, do you really need the power?

If you need the power....oxygenated race fuels are pour in power.

All race fuels you would run burn cleaner and are overall better for you bike long term....

Question is, do you really need the power?

i need less power.

Seriously, IDK bout you but thers no way that I could ever fully use all the power in my 06'. It has pure brute strength everywhere...

Seriously, IDK bout you but thers no way that I could ever fully use all the power in my 06'. It has pure brute strength everywhere...

Love the linear powerband on the 06, but frankly, my CRF has a much stronger powerband, especially the midrange in comparison, which is great on the track. In the desert, my 06 YZ had a 5th gear that never ended. It would just keep pulling and pulling forever. I still prefer the CRF's powerband however as I can accelerate quicker and not have to wait for the powerband to kick in.

The extra HP is buying you better low-midrange and torque which the YZ needs. Trust me, try some extra HP and you'll change your tune. HP is not about top speed.

I won a can of U 4.2 at a race last year, and just for the hell of it, ran it in my 07 YZ450F during a local race series. I upped the jetting (can't find the sheet I wrote it down on) and went with it. I did notice an increase in power throughout the range, but I also noticed a major improvement in starting, especially after stalling the bike. It seemed that a sneeze on the kickstarter would fire her up, compared to a couple of full body kicks running pump fuel. Needless to say, given the cost of running race fuel over a year, that improvement isn't enough for this Vet Novice racer to spend the money on race gas.

I won a can of U 4.2 at a race last year, and just for the hell of it, ran it in my 07 YZ450F during a local race series. I upped the jetting (can't find the sheet I wrote it down on) and went with it. I did notice an increase in power throughout the range, but I also noticed a major improvement in starting, especially after stalling the bike. It seemed that a sneeze on the kickstarter would fire her up, compared to a couple of full body kicks running pump fuel. Needless to say, given the cost of running race fuel over a year, that improvement isn't enough for this Vet Novice racer to spend the money on race gas.

You want to consider the Cam route. I've it to work great and it's cost effective.

Love the linear powerband on the 06, but frankly, my CRF has a much stronger powerband, especially the midrange in comparison, which is great on the track. In the desert, my 06 YZ had a 5th gear that never ended. It would just keep pulling and pulling forever. I still prefer the CRF's powerband however as I can accelerate quicker and not have to wait for the powerband to kick in.

The extra HP is buying you better low-midrange and torque which the YZ needs. Trust me, try some extra HP and you'll change your tune. HP is not about top speed.

Yeah, I like the crf engines too. I used to have a crf450 before this bike and I loved the engine as well. I just like the smooth steady power of the yz. My old honda seemed like it would rip your arms off in the mid range. For some reason, the honda just didn't click with me. The yz for me, is my optimal bike. I have a powerbomb/4.1 exhaust combo on my bike, but I was think about throwing a set of hot cams in her the next time I have to open her up...although with these bikes, that might be a LONG time. :thumbsup:

I won a can of U 4.2 at a race last year, and just for the hell of it, ran it in my 07 YZ450F during a local race series. I upped the jetting (can't find the sheet I wrote it down on) and went with it. I did notice an increase in power throughout the range, but I also noticed a major improvement in starting, especially after stalling the bike. It seemed that a sneeze on the kickstarter would fire her up, compared to a couple of full body kicks running pump fuel. Needless to say, given the cost of running race fuel over a year, that improvement isn't enough for this Vet Novice racer to spend the money on race gas.
You want to consider the Cam route. I've it to work great and it's cost effective.

I forgot to mention that I was running the jetting that came in the bike when it was taking a couple of full-body kicks to fire. Now, I've fine-tuned it and it starts first kick almost every time. I don't need any extra power from my YZ-F

I don't need any extra power from my YZ-F

Folks....Time to end this thread. He doesn't require any additional HP. Nuff said.:thumbsup:

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