Honda CB300R 2019 Owner's Manual page 48

Starting the Engine
If the engine does not start:
Open the throttle fully and press the start
a
button for 5 seconds.
Repeat the normal starting procedure.
b
If the engine starts, open the throttle slightly
c
if idling is unstable.
If the engine does not start, wait 10 seconds
d
before trying step a & b again.
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If Engine Will Not Start
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