Originally posted by cjpoole1+Dec 31 2003, 11:19 AM--></span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (cjpoole1 @ Dec 31 2003, 11:19 AM)</td></tr><tr><td id='QUOTE'> <!--QuoteBegin--YFZ439@Dec 31 2003, 11:47 AM
I believe you are mistaken Max-action. The idle is responsible for idle and just off idle, the pilot works up to about 1/4 throttle, then the needle and to a lesser degree the main, from 3/4 on it is the main. If you are good on top and bottom it is most likely your needle.
:stupid [/b][/quote]
my bad...
here is some better information:
Main fuel jet:
The proper main fuel jet will give best full throttle performance, but also affects mixture as far down as 1/8 throttle. I know you don't believe this second part, because I didn't believe it until I saw it happen while tuning an extensively instrumented test engine. Suspend your beliefs about the main fuel jet only affecting mixture when the slide is all the way up & the needle is all the way out of the needle jet and think for a minute. The main fuel and air jets feed the emulsion tube which feeds the needle jet and jet needle. When a more fuel rich emulsion is bled past the same restriction (needle jet area minus jet needle area), the engine gets more fuel. You must select the full throttle jetting first. If you go and find a needle that works with the wrong main jets, it won't work with the right ones, and you'll have to go through the needle selection process all over again when the main jets are correct. Trust me
Needle selection:
1st letter: This portion of the needle controls mixture between approximately 1/3 and full throttle. If the engine fails to respond to main jet changes, you may be too lean on this, causing the tip of the needle to be very large. This would tend to artificially limit fuel flow at full throttle, taking control of WOT fuel delivery away from the main jet. Selecting this is much easier than many believe. If you find that mixture is good at 1/4 throttle, but too rich at 3/4, you probably have a needle with too great a taper angle. If the mixture is good at 1/4 throttle, but too lean at 3/4, you probably have a needle with too small a taper angle. I know you went and made sure the main jets were sorted out before testing the needle taper, right?
2nd letter: This generally doesn't need to be played with much. If, when adjusting the clip, you find that you are at the 1st groove and still need to start the taper later, you may need to select a needle with a longer L1 dimension. If you find yourself at the 7th groove and needing to start the taper earlier, you may need to select a needle with a shorter L1 dimension.
3rd letter: This portion of the needle has the greatest effect on mixture between closed and 1/4 throttle. If the engine is too rich while gradually accelerating through 1/8 throttle, select a needle with a larger root diameter. If the engine is too lean when gradually accelerating through 1/8 throttle, select a needle with a smaller root diameter. You will drive yourself completely batty trying to sort out this if the slow fuel and air jets aren't right. Conversely, you will drive yourself completely batty if you try to sort out the slow fuel and air jets if the needle root diameter isn't right. So you're pretty much screwed either way here. And if you didn't set the float level to 9mm, just go jump off a cliff right now and get it over with because that will have a fairly large effect on how much fuel spurts up through the needle jet when the slide's only open a little bit.
Clip position: This controls mixture between approximately 1/8 to 7/8 throttle. Higher clip position for leaner, lower for richer. Unlike taper, this setting will change mixture (approximately) evenly throughout the throttle position range, with a slight tendency to affect the lesser throttle positions more than greater. You should work to find a needle which allows you to run the clip on the 3rd, 4th (middle), or 5th position. If you find that mixture at 1/3 through 3/4 throttle is too lean, raise the needle!
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