THE TwinMax TO SYNCHRONIZE THROTTLE BODIES ON THE R1100RT/R1150RT
contributions from G. McCurdy, Dick Frantz & Lee Sayers)
achieve equalized fuel/air delivery to the engine cylinders
at idle and moderate throttle openings.
result is to produce a smooth and more efficient running engine
Theory Of Operation
the tubes attached and the engine running, the difference,
if any, in the vacuum from the two sources is sensed by the
TwinMax, and presented visually by a needle on the TwinMax’s
meter face. If one throttle opens more than the other does,
it will cause the needle to move toward the hose attached
to that throttle.
operation, with the engine not running, the needle on the
TwinMax meter must be centered while the hoses are attached
to their respective vacuum source. This should be done at
the highest sensitivity setting in order to achieve the most
accurate zero setting.
the synchronization, with the engine running, the needle may
vibrate, or oscillate, in time with the opening and closing
of the intake valves depending on rpm. “Centering” the needle
to achieve equalization consists of setting the throttle openings
so as to cause the needle to swing (or oscillate) an equal
distance to either side of the Zero Point on the meter. The
most effective sensitivity setting to use during equalization
is to achieve about a º inch to 3/8-inch total swing of the
the RT Throttle BODIES is a two-step process. First the idle
fuel/air mixtures are equalized, and then the intermediate
speeds controlled by the throttle bodies (twist grip) are
both the right and left side body panels are removed to gain
access to the throttle bodies and the hose connections. Removing
the left side panel may not be required if the idle synchronization
is not bad and adjustment can be controlled by the right Air
Bleed Screw and you can attach the hose to the TwinMax to
adjustment is accomplished with the engine running at… idle.
That means with the throttles closed.
Open throttle, or intermediate speed,
synchronization is accomplished by changing the operating
length of the RIGHT SIDE throttle cable by use of the adjuster
at its end at the throttle body. This adjustment may be accomplished
at any STEADY rpm achieved by locking or holding the throttle
grip opened in the counter clockwise direction. Traditionally,
adjustment is done at 4000rpm. However, some folks feel that
2500rpm, or the speed achieved when both throttles are just
opened produces the same, or very similar results.
If you like to travel at a given speed, note the rpm
you cruise at and make the adjustment there, or at least check
it at that speed as well.
This will minimize any vibration at your favored cruising
speed. Note that
in the following text, 2500rpm is used as the reference.
TwinMax, with fresh battery, and with tubes sized for BMW’s
throttle body vacuum ports. ,
Slot head screwdriver, 3mm Allen wrench, 10mm open end, needle-nose
pliers, and room fan (optional).
the warm-up, shut the bike off and place it on the centerstand.
Remove the rubber vapor recovery tubes from the bottom side
of each throttle body.
Place the TwinMax at the seat location so that you
can view the meter’s face.
Insert the hoses from the TwinMax onto the exposed
injector throttle body taps,
A-side to the left and B-side to the right. Make sure
the TwinMax is securely positioned.
Its recommended you use a room fan in front of the
bike to provide cooling so the bike won’t overheat.
Work quickly as the bike can overheat without adequate
glance at the Rider Information Display to make sure the temperature
stays in an acceptable range.
Adjust Idle Screws (for balance throttle body vacuum at idle)
synchronization is accomplished by adjusting the large brass
Air Adjustment Screws low in the throttle body with the throttles
closed. The idle state of Closed Throttles
is confirmed by ensuring:
twist grip is in the full forward position and there is slack
in both throttle body cables.
The throttle flanges on the throttle pivots are bottomed to
the throttle stop
throttle cable displays about º to 3/8-inch play when pushed
to the side.
idle, the fuel injectors deliver a constant amount of fuel
for each cylinder firing, monitored by the setting of the
Throttle Position Sensor (TPS). Adjusting the Air Adjustment
screw varies the amount of vacuum allowed to pass to the
idle circuit, or more graphically, to allow more air to
be drawn past the closed main throttle.
these screws brings about two effects: The idle air/fuel mixture
is changed and the idle speed is changed.
to the need to maintain a viable mixture, with the TPS set
within acceptable values, idle speed somewhere in the range
of 1000rpm, +/- 50rpm should be achieved during idle synchronization.
If synchronization within these values cannot be achieved,
most probably the TPS setting must be changed. That procedure
is outside the purview of this document, and it is suggested
you contact a competent BMW dealer.
an idle speed as high as 1200rpm usually can be achieved without
concern. Much beyond this level causes a non-viable air/fuel
mixture, and may lead to an intermittent condition that is
best described a “sticky” throttle on closure, resulting in
an occasional high idle speed of up to about 1500 to 1600rpm.
Loosen the locknut on the cable adjuster on top of the right-side
throttle body cable, because this is where you will make the
part-throttle adjustment in STEP 2. DO NOT loosen and adjust
the LEFT side throttle cable, as this will effect the validity
of the TPS setting.
Turn on the TwinMax, and allow it to warm up for a few minutes.
Turn the SENSITIVITY knob fully to MAXI (full clockwise).
Adjust the ZERO knob until the meter needle is precisely through
the middle of zero on the scale; this adjustment is very sensitive
and very important.
Turn the SENSITIVITY knob back to MINI (full counter clockwise).
Start the engine and allow it to idle and again achieve normal
operating temperate of 5 bars
Slowly turn the SENSITIVITY knob until a deviation shows on
the scale. The less out of balance the two cylinders being
tested are, the more you will have to turn the SENSITIVITY
knob to show an imbalance on the scale.
Adjust the brass idle/slow running screw(s) on the throttle
body(s) until the meter shows zero. The meter is very sensitive,
so care must be taken to use small increments of adjustment.
Optimally, you want to adjust each screw by an equal
amount, but it’s possible to adjust only on one side.
Attempt to balance by using one side.
If you can’t accomplish the balance in º turn from
one side, then adjust the other side as well.
The brass bypass screws are the only screws you need to turn for the Idle synching operation. ALSO, the screws may be dirty if the bike
has 15k or so on it.
If so, Idle balance can’t be achieved. Shut off the
engine. Take the screws out and clean both of them and their seats
with a cleaner suitable for fuel injection manifolds.
Reseat them, and back out about 1 turn.
Then repeat the operation from 6.
Leave the engine running, and proceed to Intermediate
(to adjust for equal cable pull)
the lock nut on knurled cable adjuster for the right side
throttle body has not been loosened, do so now.
Start with the SENSITIVITY knob about the middle of its range.
Start the engine, open the throttle gently, and run the revs
up to 3000 or 4000 rpm.
The needle will oscillate. Your goal is to have it
oscillate an equal amount on each side of the zero position,
and about º to 3/8 inch in total width.
If the needle movement is not pronounced, increase
Using about 2500 rpm, hold or lock the throttle grip
open (if available your Throttlemeister or similar device.),
and adjust the knurled portion of the right side throttle
body cable adjuster with your other hand. The meter needle
will be oscillating.
Adjust the cable until you can achieve an equal deviation
on each side of the zero point. Let the bike return to idle
(checking needle alignment again). If all is well, shut the
After synchronizing at part throttle, tighten the locknut
on the cable adjuster, making sure that the adjuster does
not rotate with the locknut and alter your adjustment. It
is easier if you hold the knurled adjuster with the set of
needle-nose pliers while you tighten the locknut with a 10mm
wrench to prevent slippage.
Re-check that the TwinMax needle is still zeroed at
the chosen intermediate rpm after tightening to the cable
lock nut and no change has taken place.
Re-check your idle settings to ascertain that they
have not changed. You
may need to work through the synchronization adjustments for
both the Idle as well as Intermediate speeds to fine-tune
If all is well, turn off the bike. Turn off the TwinMax. Smile
about a job well done.
Reinstall the body side panel(s) if you feel it looks better