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New Jets for VP U-4?

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Hey guys, I was wondering if I was going to need to change the jetting on my '04 YZ250F when I start using VP U-4 here in a few weeks. I read somewhere that you may need to. Thanks for any help. The bike is running pretty good right now though.

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I am running some KLOTZ oxygenated octane booster with 93 octane pump gas in my 04 RMZ since I had the top end redone with a hi compression piston and it tends to spit a small flame(pop) out the exhaust when it is cold. Should I go up on the main? I am one up from stock right now.

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We deal with lot of stuff with VP since they have a district office here and a lot of my friends work for them. Also Bruce (head of VP world) is a close friend of us at the dealership.

U4 and U2 are suppose to be direct replacement fuels, IE: you should be able to run them with the same jetting. I find that on most bikes they will run a tad lean because of the weight of the U4 and U2. They will run fine in the bike, but i do go up 1 jet size in every bike i switch over to VP. I have not yet had to go up more than 1 jet size and on a few bikes the jetting seemed to be good without going up (bike was originally rich). Run it for a while and check out your plug. It will look different because it burns cleaner, it will be a silver/grayish color verses the conventional tan.

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Binder,

Thanks for the information on the VP fuels. I was given the recommendation to richen jetting by a local race fuel distributor. It appears has was being conservative or referring to another fuel.

James

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We deal with lot of stuff with VP since they have a district office here and a lot of my friends work for them. Also Bruce (head of VP world) is a close friend of us at the dealership.

U4 and U2 are suppose to be direct replacement fuels, IE: you should be able to run them with the same jetting. I find that on most bikes they will run a tad lean because of the weight of the U4 and U2. They will run fine in the bike, but i do go up 1 jet size in every bike i switch over to VP. I have not yet had to go up more than 1 jet size and on a few bikes the jetting seemed to be good without going up (bike was originally rich). Run it for a while and check out your plug. It will look different because it burns cleaner, it will be a silver/grayish color verses the conventional tan.

Thanks for the info Binder, very helpful.

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