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Old 01-14-2008, 08:41 PM   #1 (permalink)
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Jetting - How Rich Is The Jetting Chart?

If my chart says to run a 340.. what would you run?..
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Old 01-14-2008, 08:44 PM   #2 (permalink)
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Um...a 340? Check the plugs, you want them a dry brown color. If they are darker or almost black, go smaller.
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Old 01-14-2008, 09:44 PM   #3 (permalink)
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yea I know how to read the plugs. stock in my sled is a 340 (sled in sig) but it still seems rich. I remember people saying that the stock jetting charts are always rich. I was wondering if there is a set number that is a good place to start.. like taking 10 off the chart or somehthing.
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Old 01-15-2008, 08:30 AM   #4 (permalink)
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In the early 90's lots of guys just took 10 off stock polaris around here. But today you never know whats up with your gas. A little crappy gas will melt down your sweet rebuild if you get too aggressive. After melting down several 500 liquid top ends, I've learned to give up a little performance to save 500 bucks! Was it warm out when you were running rich? Lately I've been jetting rich for cold timps then I drop the needles a notch if it gets real warm.
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Old 01-15-2008, 12:09 PM   #5 (permalink)
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Remember, Ngk Plugs Get Colder The Higher The Number, Hotter The Lower The Number.
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Old 01-15-2008, 12:50 PM   #6 (permalink)
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So if my plugs seem to be running a little too rich would it be best to drop one number ngk plug size before you try dropping a main jet size? The chart for my 1990 Indy 500 jet size chart says in my altitude 1500 ft at -30 to 0 (F) run a .280 jet and from 0 to +30 (F) run a .270 jet. The factory jet they install is a .280 but with the global warming or whatever it seems now days I am running in warmer temps most of the time these days I would say most of my riding has been in +10 to +30 (F) so I bought new .270 jets to put in. I wonder how much risk it is if I happen to run it say -10 to 0 (F) with the smaller jet? It would be easier to change to a one number larger (colder) ngk plug than change jets for below zero temps that seem to only last a day or 2 now days. Does this make sense?
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Old 01-15-2008, 05:13 PM   #7 (permalink)
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I would not go lower than 280 on that unit. The first time I burned down my 1991 Classic it had 270's in it. If you start going that lean you better be darn sure you have clean carbs and good gas. If it runs unbelievable, its too lean. If its warm, drop the jet needles to a "2" but watch those plugs!
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Old 01-15-2008, 06:54 PM   #8 (permalink)
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Then why would the chart under the hood say 0 to +30 (F) run a .270 jet? I am going to try it and keep checking the color of my plugs. I bet over 90% of the time I am running in +10 to +30 (F) degree temperature. I wouldn't care except when I run in about +20 temp it keeps back firing in the exhaust when I let off the throttle, and when it is colder out say +15 or lower it doesn't do it.
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Old 01-15-2008, 08:19 PM   #9 (permalink)
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Dropping 10 isn't going to hurt it, but CHECK YOUR PLUGS!!! If they are getting too light of a tan color, rejet it back.
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Old 01-15-2008, 08:21 PM   #10 (permalink)
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ok.. I will throw the 330;s in.. I ordered 310,320,330, and 350's just to be safe.. Its kinda alot of work to rejet so I wanted to get an idea of what to start with.. thanks
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Fresh Rebuild 12/1/07
Parts Unlimited Pistons/Rings
Bored 30/1000's
Shaved Head
3" Bar Riser
2,200 Miles
(Dont Forget To Grease Your JackShaft Regularly)
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