2007 YZ450 running VP U4.4

I purchased a 5 gallon drum of VP U4.4 to run in my yz450. I read as much as I could regarding the debate about race gas being worth it or not, and decided to try it out. I understand that there is not much to gain as far as power without ignition timing changes, but I thought it would be worth it for a cleaner burning fuel, non-ethanol blend. I also hope that the lead would provide benefits.

Please don't take this into a debate about the cost of fuel, I probably only used about 1 to 1-1/2 gallon for a hour and half track ride. The cost difference for the day was really only like 10 to 15 dollar difference between pump fuel and race gas. I don't get to ride too often so long term the cost will probably be only 100-200 dollar difference a year, maybe. Plus the metal can for fuel storage will be used for the lawn equipment. :thumbsup:

All I can say is I noticed a much crisper throttle response, well worth every penny imho. I really feel it made a significant noticeable difference. This may be because my bike always was a bit rich to start off, who knows.

My jetting stock on the bike has always been a tad rich based on assumption only in stock configuration. I poured in the race fuel without any jetting changes and the bike ran awesome, although the fuel screw was turned out past 3 turns. I went one step richer on the jetting to a 48 pilot and a 162 main per the recommendation from VP. I ran the bike most of the day around 2 turns out on the fuel screw and at the end of the day went to about 1-1/2 turns out on the fuel screw. Very little to no decel popping, I probably could go a little more lean on the pilot circuit?

My concern is this, I have a tachometer/hour meter on the bike and I follow the guidelines set forth in the thumperfaq stickies on how to jet a carb, but I dont notice a big difference. I set the idle a little high around 2000 rpm's and tamper with the fuel screw without much noticeable difference in rpm's or idle smoothness. I guesstimate that the fuel screw should be out about 1-1/2 turns. Any recommendations?

Edited by motorcross242

If you can't get the idle to fall off a little by running the pilot screw in closer than a half turn out, the pilot is likely too big.

I think that you have misunderstood some of the facts regarding race fuel in general, and U4 in particular. Timing changes are not required to make use of the potential power gains (nor, incidentally, are they necessarily likely to produce any gains at all). This is a misconception created by the incorrect notion that the power gains come from the extra octane, and that the only way to get at the additional power is to make the engine require the additional octane by raising the compression or advancing the timing. These assumptions are wrong. Higher compression does often create a need for more octane, but it is the compression ratio increase that you gain power from. Higher octane simply enables that.

Race fuels produce more power than most typical pump fuels because the fuel blend itself contains more energy potential than pump gas does, simple as that. U4 is one of those race fuel that is oxygenated, which is to say that while it burns, it releases oxygen from compounds within the fuel into the combustion reaction to add energy to it. The additional oxygen is oft times enough that it requires richer jetting in the main circuit to compensate.

You are exactly correct, thank you for your explanation.

Based on information I've collected, would you agree with the following to be worth it considering its maybe 10 bucks more a trip for me a few times a year:

- Ethanol-related problems will not be an issue and you can expect better vaporization, plus a cleaner, more efficient burn than that of street gas.

Well, I don't know what you paid for the U4, and I don't know what part of the state you're from, but U4 would cost me over $17 more for each gallon than the pump gas I run and don't have any trouble with. I'm in San Diego County, BTW.

Well I did pay the full price on this first can to try it out (which was close to 100), but I met someone in the VP booth at A3 who can deliver it in my area for 73 bucks for my next can. He also gave me a 5 dollar coupon so for 68 bucks, its 14 bucks a gallon. 5 gallons will probably last me 4-5 trips to the track.

After it's all said and done, I guess I'll decide if the extra 10-14 bucks a trip is worth it.

I would just like to warn anyone who is thinking about using VP U4.4 about possible damage it may cause. I have a sticky exhaust valve, possible valve/piston damage that I would attribute the problems to the U4.4 I ran once! Having a bike, that is in 100% mechanical shape, all of a sudden have no compression? Especially after having a track day where the bike ran fine?

I called VP, which is ridiculous by the way. There is only one person who can handle technical questions for MX fuels, someone who you have to call on their cell phone. Very unprofessional, making accusations about something I may have done wrong. Playing stupid.

I should have just stuck to pump gas, as I've never had any problems. All this talk about ethanol, being problematic, bs. More like stay away from anything with VP's name on it.

I am now trying to decide about a complete rebuild, valves, head, piston, etc. Great!

Edited by motorcross242

I have a sticky exhaust valve, possible valve/piston damage that I would attribute the problems to the U4.4 I ran once!

Tell me why you would think that.

Not sure which you are referring to?

#1 - Why would I think the U4.4 caused a problem?

Based on the reputation for Yamaha's to have superb reliability I find it very, very hard to believe that this is a mechanical issue. The reason I believe this, is my valves are still within spec, and the timing chain did not slip timing. Also, if this was a manufacturing defect, what is the likelyhood of this happening the day I use race gas? Personally I take extremely good care of this bike, such good care to the point of being OCD about maintenance. I planned on keeping this bike forever. I do not know all that is involved with how or why an exhaust valve could be stuck open randomly after sitting for a few weeks. I've owned this bike since brand new and have changed my oil and filter every ride. Even some rides being less than an hour or two. I'm so bummed that I put so much time and $ in making sure this bike sees and is treated the best and its roached. Like I've mentioned in another post, I believe the U4.4 gummed up the exhaust valve. Maybe it was my fault, maybe the bike was on the rich side. I can do basic jetting, based on what I hear, feel, and see. Maybe its my fault for testing with new products that I dont know everything about. I know I read a lot about U4.4 and it seemed like a pour in replacement with only "modest jetting changes" - VP.

#2 - Why would I think I have possible damage to valves/piston?

I believe I have possible damage, because I tried to kick the bike like normal and there was no compression. Sometimes when I kick, I don't catch TDC and it takes a few kicks to get the compression stroke. I must have kicked the bike 10 times until I took my helmet off and realized the noise (clicking). This must have been the piston hitting the stuck open valve? What kind of damage could someone do to piston/valve from trying to kick over? Also, I put the bike and gear and was debating about bump starting the bike. I didn't. I did walk the bike in gear and it rolled some what freely.

I'm very nervous about riding the bike in its current state. (a bit ocd) It appears to be in normal operation after riding up and down the street. Starts just fine, sounds normal.

I'm debating selling the bike, because I know I'll be ripped off by all the local motorcycle dealers/mechanics. Trust me, I've already inquired I'm not going to invest 2k into a bike thats worth only that. Thinking about going to a YZ250.

Gray - Based on the knowledge/expertise/skill you display I would even go as far as to say, I'd trust and pay you to break the bike down and see if damage was done. And if needed, repair. I know that ain't going to happen, so now what?

Edited by motorcross242

Based on the knowledge/expertise/skill you display I would even go as far as to say, I'd trust and pay you to break the bike down and see if damage was done. And if needed, repair. I know that ain't going to happen, so now what?

Depending on where you live, it could happen. PM if you're near San Diego. But here's the thing about U4.4. It's a heavily oxygenated fuel, meaning that the combustion process releases oxygen into the reaction, which has the effect of rendering any particular jetting setup fairly significantly leaner than it was on non-oxygenated fuel. OTOH, pump gas in California is almost universally oxygenated, although to a lesser degree, mostly, and with more inert ingredients than u4, so if the bike was running OK on pump stuff, it shouldn't be too far off on U4. This is especially true if as you say, the bike was a little rich originally.

The primary causes of a valve actually becoming stuck part way open are most all related to carbon build up on either the valve stem where it meets the guide, or on the back of the valve head. U4 is much cleaner burning than most Cal gas, so it's very, very unlikely that it's to blame for a condition such as that when you only ran the stuff once. Another thing that occasionally happens in coastal or humid areas is that when the bike sits for a fair amount of time, and happens to have been stopped with a valve open, the seats, being cast iron, can rust. If this goes far enough, it can keep the valve from seating until the rust goes away.

A valve can be bent without skipping time if the springs become weak or broken and allow valve "float" at high speeds, a condition where the valve fails to follow the camshaft back down because of excessive inertia during opening. The valve that's bent will have excess clearance at the cam, making it appear "stuck open" from that perspective.

IMO, the U4 is not very likely involved in this in any way, and the whole thing was entirely coincidental. Since VP cleaned up the blend, no one I have heard from has reported any problems with 4.4. U4 and U4a used to gum up the fuel systems with a nasty white jelly if it sat in the bike very long at all, but that was it.

I would agree with grayracer on this. I have been running U4.4 for about 3 years now. First on a 2007 YZ450F and now on a fully modded factory 2010 YZ450F. No problems with either bike. My 2007 had 60 hours on it when I changed out the piston the first time and no valve problems at all. I put in a high compression piston at that time. Didn't touch the head that time around. Valves were in spec still. At 85 hours, I sold the bike and got my new one. New owner has not had any issues with the bike either although he does run normal pump gas in it. I ran that bike for approx. 60 hours on U4.4 and had zero issues with it. You don't even need to drain the carb with the U4.4 like you had to do the older formula's.

I have left over about 4 gallons of this stuff. It's been over 6 months in the metal container in my garage. Is it still any good even though it's been opened??

Edited by motorcross242

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