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Robspring81

'08 Jetting question

8 posts in this topic

Anyone got the hot setup for 2000-3000ft in the so cal desert? I ordered a Zip-TY Fuel/Air screw to cure the bottom bog blues and I am thinking of stepping up to a 165 main and a 48 pilot....any input???

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Ahhhh young Jedi....needles are available with different taper profiles to tune carb performance. They are typically labled using a letter code (or sometimes combo of letters and numbers), in the same way that jets are labeled with a number system correlating to size of the hole/passage. Your bike comes stock with an NLFP needle, the NFPP needle will have a different profile and looks like some are using that as part of the jetting setup they have arrived at that works for them, although most on the above referenced thread are using stock. If you want to get really technical, you can find info on what each letter refers to as part of the description of the taper.

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What is an NFPP needle??
Information on the different needles available is in the tuning section of your manual, along with part numbers.

All NFL* and NFP* needles have the same taper profile. The third letter in the string tells how high the taper is on the needle. The difference between the NFL and NFP is that the taper is lower by half the difference between two clip grooves on the L series. Thus, an NFLR is one half clip leaner between 1/4 and 3/4 throttle than an NFPR if both have the clip in the same position.

The 4th letter has to do with the diameter of the straight portion of the needle. This has the greatest effect on mixture from 1/8 to 1/4 throttle, as the carb transitions from the pilot circuit onto the main circuit. Here, the ID letters are sequential, from rich to lean (because it runs from smaller to larger diameter). An NFLQ needle, then, would be one increment richer from off idle to 1/4 throttle than an NFLR, but the same after that.

In the particular case of the NFPP vs. NFLR, the former is one half step richer from 1/4 to 3/4 throttle, and two steps richer from off idle to 1/4. The half step at higher throttles is probably not a big deal, but the change to the straight section may be. What Todd has done by going this route is to add fuel during the transition phase to help with throttle response without richening the idle mixture to the point that the bike runs dirty or is hard to hot start, which is the approach too many people take, IMO. He says it works well for him.

Actually, having just looked at both, the tuning section of the '06 or '07 manual is more detailed than the '08. You might want to download one.

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Wow,, I thought jetting a bike was already a little complicated, the whole needle thing and letter codes just doubled the complication level. The JD jetting kit, are they a good investment? It comes with two different needles for different altitudes. Not sure what the letter codes are for the needles, imagine I could call JD jetting and find that out.

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At least some of JD's needles cannot be categorized by Keihin letter codes, as some will have multiple tapers. His jet kits do usually work well, but they may be more expensive than buying your own pieces. On the other hand, in the event that they work out well for you, they can save a lot of time.

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