Yamaha YZ125 2019 Owner's Service Manual page 222

ADJUSTING THE JET NEEDLE GROOVE
POSITION
Should the engine be hard to run smoothly at
intermediate speeds, the jet needle "1" must be
adjusted. If the mixture is too rich or too lean at
intermediate speed operation, irregular engine
operation and poor acceleration will result.
Whether or not the richness of the mixture is
proper is hard to be determined by means of
the spark plug and therefore, it should be
judged from your feeling of actual engine oper-
ation.
1. Too rich at intermediate speeds
• Rough engine operation is felt and the en-
gine will not pick up speed smoothly.
In this case, step up the jet needle clip by
one groove or 0.5 groove and move down
the needle to lean out the mixture.
2. Too lean at intermediate speeds
• The engine breathes hard and will not pick
up speed quickly.
In this case, step down the jet needle clip by
one groove or 0.5 groove and move up the
needle to enrich the mixture.
Standard clip position
ADJUSTING THE JET NEEDLE
On the carburetors used in the YZ125, the main
nozzle is a non disassembly type, so it can not
be replaced. Therefore, carburetor setting re-
quires the change of the jet needle.
1. The jet needle setting parts, having the
In the case of the same number of clip position,
changing from 6BFY43-74 to 6BFY42-74 has
the same effect as a lowering of 0.5-clip posi-
tion. And in the case of the same number of clip
position, changing from 6BFY43-74 to
6BFY44-74 has the same effect as a rising of
0.5-clip position.
No.3 groove
7-3
same taper angle, are available in different
straight portion diameters and in different ta-
per starting positions.
Standard jet needle
A. Difference in straight portion diameter.
B. Difference in clip position
a. Reference needle
b. 0.5 richer
c. 0.5 leaner
ENGINE
6BFY43-74
6BFY43-72
6BFY43-73
6BFY43-74
6BFY43-75
6BFY43-76
6BFY44-74
6BFY43-74
6BFY42-74