Special Tuning Conditions; Pre-Adjustment Checks - Honda CRF150R 2020 Owner's Manual & Competition Handbook

Special Tuning Conditions

There are some unique atmospheric conditions or
situations that may require additional adjustments.
It should not be necessary to go more than one jet
size richer or leaner to fine tune your CRF. If larger
jetting changes are necessary, check for air leaks,
blocked or restricted exhaust or fuel systems, or a
dirty air cleaner.
Condition Main Jet Adjustment
long straights next larger
uphill sections
sand
mud
high humidity next smaller
raining
hotter than 113 °F (45 °C)
Once you've adjusted the carburetor for
temperature and altitude, it shouldn't need major
readjustment unless race conditions change
drastically. However, there are some unique
atmospheric conditions or race day situations that
may require additional adjustments. They are as
follows.
To prevent engine damage, always adjust the main
jet before adjusting the jet needle. Always choose
the next richer jet if there is any doubt so there is a
margin for safety.
Main Jet • Go richer on the main jet by one
size when: the track has a very long
straightaway or uphill section, a
high percentage of sand, or the
track is muddy.
• Go leaner on the main jet by one
size when: it is very humid or
raining, or it is hotter than 113°F
(45°C).
After using the chart, and making any adjustments
for special conditions, it shouldn't be necessary to
go more than one jet size richer or leaner to fine
tune your CRF. If larger jetting changes are
necessary, check for worn crankshaft seals, air
leaks, blocked or restricted exhaust or fuel
systems, or a dirty air cleaner.
Carburetor Adjustments & Tuning Tips

Pre-Adjustment Checks

Before adjusting carburetor settings, check the
following:
• air cleaner
• air leaks
• float level
• clogged carburetor jets
• spark plug fouling (improper heat range or
other cause)
• freshness of fuel
• owner modifications (such as exhaust system,
holes in the air cleaner housing, etc.)
• ignition timing
• compression
If the above check out, adjust the carburetor for
your specific racing conditions. Engine response
and appearance of the firing end of a spark plug are
highly indicative of the engine condition.
Refer to the list on page 143 for the optional
carburetor parts.
To prevent engine damage, always adjust the main
jet before adjusting the jet needle. If there is any
doubt — always choose the next richer jet so there
is a margin for safety.
119
Adjustments for Competition