Yamaha YZ250F(Z) Owner's Service Manual page 187

ADJUSTING THE LEAK JET
(ADJUSTING THE ACCELERATOR
PUMP)
The leak jet "1" is a setting part that
adjusts the flow of fuel discharged by
the accelerator pump. Since the ac-
celerator pump operates only when
throttle is open, the leak jet is used to
adjust a fuel mixture ratio for quick
throttle opening and is therefore dif-
ferent from other setting parts that ad-
just a fuel mixture for each throttle
opening (each engine speed).
1. When the engine breathes hard in
quick throttle opening, select a
leak jet having lower calibrating
No. than standard to enrich the
mixture. <Example> #70 → #60
2. When rough engine operation is
felt in quick throttle opening, se-
lect a leak jet having higher cali-
brating No. than standard to lean
out the mixture. <Example> #70
→ #80
Standard leak jet
* Except for USA and CDN
CARBURETOR SETTING PARTS
Main jet Size Part number
Rich #190 4MX-14943-45
#188 4MX-14943-95
#185 4MX-14943-44
#182 4MX-14943-94
(STD) #180 4MX-14943-43
#178 4MX-14943-93
#175 4MX-14943-42
#172 4MX-14943-92
Lean #170 4MX-14943-41
Pilot jet Size Part number
Rich #50 4MX-14948-07
#48 4MX-14948-06
(STD) #45 4MX-14948-05
*(STD) #42 4MX-14948-04
#40 4MX-14948-03
Lean #38 4MX-14948-02
Jet nee-
dle
Rich NDJN 5TA-14916-JN
(STD) NDJR 5TA-14916-JR
Lean NDJU 5TA-14916-JU
Rich NCVN 5TA-14916-VN
Lean NCVU 5TA-14916-VU
Rich NFLN 5TA-14916-LN
#70
*#110
*(STD) NHKR 5TA-14916-KR
Lean NFLU 5TA-14916-LU
Rich NFPN 5TA-14916-PN
Lean NFPU 5TA-14916-PU
Leak jet
Rich
(STD)
*(STD)
Lean
* Except for USA and CDN
Size Part number
NDJP 5TA-14916-JP
NDJQ 5TA-14916-J1
NDJS 5TA-14916-JS
NDJT 5TA-14916-JT
NCVP 5TA-14916-VP
NCVQ 5TA-14916-V1
NCVR 5TA-14916-VR
NCVS 5TA-14916-VS
NCVT 5TA-14916-VT
NFLP 5TA-14916-LP
NFLQ 5TA-14916-L1
NFLS 5TA-14916-LS
NFLT 5TA-14916-LT
NFPP 5TA-14916-PP
NFPQ 5TA-14916-P1
NFPR 5TA-14916-PR
NFPS 5TA-14916-PS
NFPT 5TA-14916-PT
Size Part number
#40 4JT-1494F-03
#50 4JT-1494F-07
#60 4JT-1494F-11
#70 4JT-1494F-15
#80 4JT-1494F-19
#90 4JT-1494F-23
#100 4JT-1494F-27
#110 4JT-1494F-29
#120 4JT-1494F-31
#130 4JT-1494F-33
#140 4JT-1494F-35
7-3
ENGINE