VP U4.4

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who_gives_a6 · #1 Post by **who_gives_a6** » Sun Apr 20, 2014 5:15 am

Anyone run this? I got a couple containers basically free recently. NOTICEABLE DIFFERENCE. Much snappier and runs so smooth. Starts faster than ever cold or hot. Had to add fuel in the map for it since it's oxygenated.

My questions is has anyone had issues running this? Mainly with boiling. I had the headers wrapped and heat tape on the bottom of the tank, and I try to keep the tank topped off. However, if it drops below half a tank it starts to boil it seems and then the fuel pump seems to starve and dies. Cool off and good to go. Any suggestions or prior experiences? They talk about it boiling easy on the VP site so figure our tank setup doesn't help.

MX Quad Dad · #2 Post by **MX Quad Dad** » Sun Apr 20, 2014 1:09 pm

we ran VP fuel in our Moto mainly to insure we didn't get bad pump fuel but the oxgenated fuel was not AMA legal (not that they ever checked) so we didn't use any thing oxgenated. the people at VP were very helpfull with choosing a fuel and other tips like storeing

We ceramic coated our header pipes because it was suposed to help reduce heat loss, plus we also wraped it.

One of the TSB was to reroute the fuel line and not run it over the head. not sure if that is possible with the newer tank. and I think both lines need to be insulated and run in the coolest location possible. with oil in the frame and the air flowing back to the tank also adds heat to the fuel plus the constant circulation doesn't help when it is allways in an insulated fuel line. just the constant pumping alone will build some heat.

would be fairly cheep to zig zag a steel brakeline in front of the radiator to see if it might help

who_gives_a6 · #3 Post by **who_gives_a6** » Mon Apr 21, 2014 1:19 am

Just gave up with it and have sold some/posted the rest of the U4.4 on Craigslist. Was 91 today and couldn't even get 10mins on it. Swapped back to premium pump gas and can run as long as I want again immediately. Just sucks because the U4.4 makes a noticeable difference when riding and smells nice even.

Didn't have the issue running VP 110 and mixtures before. But guess our machines just can't do leaded and oxygenated fuels when it's hot outside.

MX Quad Dad · #4 Post by **MX Quad Dad** » Sat Apr 26, 2014 6:40 pm

I have run several leaded fuels includeing aviation 100 and the only one I have had problems with were bought at gas stations and one area supplier and were called race gas. I learned that around here a lot of stations that sell race fuel use the same pump and tank to sell Kerosen in the winter months. VP also gave me tips for storing fuel

wistech · #5 Post by **wistech** » Sat Apr 26, 2014 7:02 pm

Ive had a couple of boiling episodes with the u4 at the dunes and in gravel pits where its slow speed hillclimbing in the heat. I purchased a couple of these heat exchangers to install in front of the radiator but we have not had a dune trip in a while to test them out. A small fan computer fan fits these perfectly . If you want one PM me and Ill sell one cheap.

MX Quad Dad · #6 Post by **MX Quad Dad** » Sat Apr 26, 2014 10:15 pm

QUOTE (Wistech @ Apr 26 2014, 03:02 PM) <{POST_SNAPBACK}>

Ive had a couple of boiling episodes with the u4 at the dunes and in gravel pits where its slow speed hillclimbing in the heat. I purchased a couple of these heat exchangers to install in front of the radiator but we have not had a dune trip in a while to test them out. A small fan computer fan fits these perfectly . If you want one PM me and Ill sell one cheap.

Have you ever run a leaded gas in the dales? we ran a leaded VP and fuel from a local airport in our Moto (stock), and it ran good. I'm tinking the other race fuel we had problems with were from the stations that used the tank and pump for kerosen and now Im thinking this was before we got the Moto, so we were lucky enough not to have put it in our Dale. banshee and pull tractor were not so lucky allthough it really didn't hurt them other than performance. a local supplier sold a 104 leaded fuel which gave us problems and when we inspected the fuel it had a whiteish cloud floating in it. a VP rep told me it was the lead and asked if it was stored in an above ground tank, which it was

wistech · #7 Post by **wistech** » Sat Apr 26, 2014 10:35 pm

Ive used mr109,u4 and it derivatives , renegade fuels , and 110vp from the local pump the only one Ive ever had any trouble with was u4 for boiling. I must say mr109 was very impressive for lower compresion engines.

Canniboomer · #8 Post by **Canniboomer** » Sat Apr 26, 2014 11:44 pm

Do you have my high flow pump inlet?... can't remember if I sent you any kit, or partials.
And does it have full 1/4" flow fittings, at least, ALL THE WAY to the pump?... or merely stock fittings that are drilled out?, and therefore still only a meager 1/8" fuelpath?... not good enough for running U4 in our hot southwest desert.
The so-called boiling will start in the suction line or in-tank tube itself. It has to start there first, because all liquids boil sooner at lower pressure. The more sucking restriction the pump has, the more vacuum in the suction line, and the sooner that vapor locking will happen, which is
exactly as the symptoms describe. A clogging fuel filter will also cause earlier boiling.
If you come out of the tank with full 1/4" flow fittings, and then transition to a 5/16" in-out filter and then 5/16" smooth into the pump, that will certainly max out the boiling point of any fuel used.

wistech · #9 Post by **wistech** » Sun Apr 27, 2014 2:02 am

For those who have never experienced this issue its unmistakable. https://www.youtube.com/watch?v=Jh9V2PGfCMc Cannondales are cooler because you can see it when you take the seat off. It might be better to just go with a fuel with a higher vapor pressure on the super hot days. The times Ive had it happen it was a half hour wait till the fuel stopped perkolating. We switched to regular gas and didnt have any more issues.