TILLOTSON TCT User manual

Adjusting your Tillotson TCT
There are two primary methods of adjusting the TillotsonTCT fuel system. The first method
is to adjust only the idle speed through the idle speed screw. This adjustment is done if
engine is hunting or not running steady only at idle. The second is to adjust the air-fuel
ratio through the AFR screw. This adjustment adjusts the amount of fuel being delivered
from idle through wide-open throttle and is used if the engine is hunting or running
abnormally at more than one speed or if the problem is not corrected through adjustment of
the idle screw (possible causes include operation at altitudes greater than 400m (1312 ft)
above sea level or a change in the grade of fuel used).
1. Adjusting the Idle Speed Screw.
If the engine is hunting or running improperly only at idle, you can adjust the amount of fuel
being delivered at idle by turning the idle speed screw with an allen key. Turning the screw
clockwise increases the idle speed. The gauge on the top of the TillotsonTCT shows how
many degrees the throttle shutter is open. If adjusting the idle screw does not solve your
problem, return it to the original position and adjust the AFR screw as shown in the next
step. If the engine still does not operate operate properly, first open the idle screw a few
degrees at a time, then adjust the AFR screw up to 1/2 turn.
Figure 1.1
On Tillotson vertical engines, the idle speed screw is accessible through a hole in the air
filter cover.

A. Remove the Cover Plug A (Figure 2.1)
B. Place screwdriver into the well and seat the screwdriver in the slot of the AFR screw
(Figures 2.2 and 2.3)
C. Turn the AFR screw in 1/8 turn increments, counterclockwise to make the fuel
mixture richer or clockwise to make the fuel mixture leaner (Figure 2.4). If the
engine continues to run rich or lean after the initial adjustment, a further adjustment
in 1/8 turn increments may be necessary.
small flathead screwdriver
Figure 2.2
A
Figure 2.1
Figure 2.3
Figure 2.4
Turn counterclockwise in
1/8 turn increments up to
1/2 turn to make richer.!
Turn clockwise in 1/8
turn increments up to 1/2
turn to make leaner.!
2. Adjusting the AFR Screw.
If the engine continues to hunt or run improperly at speeds other than idle, you can adjust the
entire air-fuel mixture range by adjusting the AFR Screw. On models with the EPA limiter
screw, the adjustment is made with a small flathead screwdriver. To adjust:

Technical Data
Figure 2.2
B
C
D
E
B) AFR screw
C) Fuel needle
D) Cam Follower
E) Cam
How the AFR Adjustment works: The
The AFR screw adjuststhe needle
height relative to the cam position.
Full Adjustability: The TillotsonTCT technology also permits the engine to meet emissions at all points of
adjustment within normal operating paramaters (that is, prior to substantial degredation in engine performance ).
Raising the needle richens the mixture (increases the fuel)
while lowering the needle leans the mixture (reduces the fuel).
For most 160-208cc engines, normal adjustment
parameters is +/- 1/2 turn from standard.
*The Black line indicates the ideal AFR curve, where we set the engine to operate to minimize emission and
maximize performance and and fuel economy. The AFR is approximately 14.5 at idle and the H
+NOx emissions are 6.5 to 7.5 g/kWh.
*The Red and Blue linesindicate the normal adjustment parameters, +/- 1/2 turn. Engine performance begins
to degrade beyond that range. The engine is still well within emissions parameters, with H+NOx emissions at
about 8.5-9 g/kWh.
*The black dotted and dashed lines indicate where the engine begins to violate emissions. Before reaching
the black dashed line, the engine is running too lean and hunting. Before reaching the black dotted line, the
engine sounds bad and is smoking under load.
*CO emissions are within guidelines at all curves.