Chapter 5 – Fuel feed system
Service manual AJP PR3/PR4 5 - 21
Note:
In carburetors equipped with
acceleration auxiliary pump (Power Jet) the
access to the idling screw becomes more
difficult and may require the use of a small
specific tool (a handmade screwdriver, with
the necessary curves to access the idle speed
adjust screw), as can be seen in the following
figure.
By rotating the screw towards clockwise
increases the engine rpm; if loosened, by
turning the screw in the anti-clockwise
decreases the engine rpm.
Air / fuel mixture adjustment screw
The adjustment screw of air / fuel mixture is
located at the bottom of the carburetor, along
the inlet flange.
By rotating the screw in a clockwise direction
decreases the amount of fuel (lean mixture),
by rotating in the opposite direction increases
the amount of fuel (rich mixture).
Note:
The mixing screw is already adjusted from
factory but due to the pressure difference
related with altitude in some regions, it may
be necessary to adjust it according to the
needs.
Close the mixture screw until it touches
their settlement (do not tighten).
Loosen the mixture screw in 2 ¼ turns. If
necessary, loosen or tighten the screw
from that initial adjustment.
Mixing screw adjustment: 2 ¼ turns.
To be easier to access and adjust the air / fuel
ratio adjusting screw is recommended to use
a special tool as shown in the above figure
and should be identified in the following
similar figure.
