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Jetting with CHP pipe and U4?????

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I have been using U4 mixed 50/50 with pump gas and just got a new Classic Ultima pipe. I have tried a few plug chops and I keep going up on the main but I am still getting some white on the insulator. Here's the kicker, it has run good with no popping on every main. I started with a 105, then 110, 115, 120, and now a 125.

GPX 131 HC

CHP pipe

Oil sling and flywheel mod

Cat 5 head

tb26mm carb

Any advice????

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The U4 wants more jet over regular pump gas. Usually about 1-2 sizes. But a properly jetted 4 stroke shouldnt show anything on the plug. The plug should look like it just came out of the box. You can read the plug if you want to run the U4 alone, but when you pollute it with pump gas your basically wasting what ever gain you may have gotten on the U4.

The real way to jet U4 is by reading the exhaust pipe. It should be gray an inch inside the muffler. On pump gas it'll be black almost regardless of what you do with the jet. If you try to jet pump gas by reading the plug, by the time you get any color on the plug its going to be way rich and run lazy.

Most of this is fourstroke jetting 101

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Thank you for the help. I mix the U4 with pump gas to gain the oxygen content from the U4 (I live @ 5k ft.), and U4 is the only oxygenated fuel that I can find around here. Are you telling me that I should IGNORE the white plug!!!!

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The plug should be clean. When you say white, are you talking about the plug shell or the porcelin insulator or ground wire or what?

It really doesnt matter much...basically the thrust is you can accurately jet the bike with pump gas by reading the plug.

The crap in regular pump gas is random almost and changes from season to season that you cant rely on what the plug tells you. And that leaves you with jetting by the seat of your pants. If its running harder and harder the bigger the main jet gets, keep going until it gets lazy then back up on the jet sizes and you should be done. The problem is the oxy content of the pump gas is going to change up and down so if youre trying to jet to the cutting edge...youre going to spend a lot of ride time dicken with the jetting. With a mini...they dont burn much fuel anyway so just run the U4 straight and then you can read the plug and get the jetting right and be done with it. One thing to remember, U4 varnishes up reall quck if you leave it in the carb. Even just a week could easily plug the pilot jet.

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I would say get some 100 octane if you can find it. Don't even mess w/ the U4. I have a 131hc piston in mine. Still have 92 main but I am running a 22mm carb and CHP pipe. W/ 93 octane I was getting a bit of spark knock so I have since been running 50/50 mix of 93 and 100 octane. This way I don't get spark knock but I can still read my plug. Puts out 9.6hp so I don't see a need for oxygenated fuels.

Shawn is right though. It does take a while to notice the difference on the plug after a jet change even w/ pump gas. Mixing pump gas and U4 is kind of a waste too.

Also, what kind of air filter are you running? I was running a Uni and had mine dialed in. Went to a different filter and boy did my bike go way rich. I had to drop 6 main jet sizes to get it right. I have since went back to my UNI.

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I am using the Uni filter, and I am using the U4 mixed with 92 because I live at 5000ft. I really need the oxygen in the fuel to compensate for the lack of it we have in the air.

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Run it on one or the other and jet it like that. Whichever you choose. If you jet it on pump gas and get it right you should just be able to go up a couple of jet sizes and it will be right for U4. I understand you are in a bit of a pickle at that elevation for power. I would probably stick w/ straight U4 and jet it that way.

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