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Moto-Mike

Needle in a haystack...YZ timing!

3 posts in this topic

I am about ready to try YZ timing and am a bit confused on which needle jet to use.

Some people are running the stock 'DRS' while others are running the 'DVP'. What is the difference? This years carb comes with a 'DRS' and the 98 and 99's must have came with a 'DTM'. Does last years "needle of choice" the 'DVP' the best choice for the 2000? Thanks for any help/recommendations on this matter-

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2000 Yamaha WR400F

1988 Honda NT650 Hawk

1977 Suzuki RM250B

1974 Honda XR75K1

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Moto-Mike and interested others,

Start by reading the owners manual section on carb tuning and I will guide you through the needle codes and corrections to the figures shown.

(A major factor here is the carbs are different but the needles can be used in both)

- needles :DTM,DVP,DVR,DRS

- first letter: D = .75 degrees taper, the same for each and affects 3/8 to 3/4 throttle. (YZ426 uses E = 1.0 degrees and is richer in this range)

- second letter: T,V,R, these refer to the distance from the clip to mid taper. This affects 1/8 to 1/2 throttle. All DR- needles are 1 clip richer than all DT- needles. All DT- needles are 1 clip richer than all DV- needles. Think of the second letter as nothing more than changing the clip position. Thus a DRP-#2 clip equals DTP-#3 equals DVP-#4, no difference in jetting at all.

- third letter: M,P,R,S, these refer to needle straight diameter and affect only 0-1/8 (or at most 1/4 throttle). M is the most rich (2.715mm), then P (2.735mm), R (2.755mm), S (2.765mm). This is low throttle jetting only.

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Now what to do with a '00WR DRS needle? - it has a richer clip location and a lean straight diameter so to make a best guess try a DVP or DVR and go 1 clip down. This will richen 0-1/8 throttle and lean out 1/8-1/2 throttle. ( 2 clips lower will be equal jetting at 1/8 to 1/2 throttle - DRS#2 & DVR#4 are nearly identical) Don't try the DTM unless you want a big change richer 0-1/8.

(The short answer - DVP#4 to start with)

Good Luck !

James Dean

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Thanks J.D. Whew that's some pretty technical stuff...my brain has a hard time following all those variables in those codes. :) I'll go with your short answer and order the 'DVP' tommorow. Thanks again!

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