This is the
"Idle Drop" method described in the Honda Service Manual for the
Shadow Sabre. Many have elected to simply richen/lean their carbs
until their problems disappear (popping on decel, etc.), and have
had no problems. However, if you have a service tachometer, you
can use this method. This method will also have the result of
setting your idle speed to factory specs.
Manual (page 5-18 and 5-19)
- Tachometer (capable of showing 50 RPM changes in engine speed)
(flat-head) screwdriver small enough to reach pilot screws
screwdriver small enough to fit into frame neck cover screws
with 12mm, 10mm, and 8mm sockets, and a 6" extension
- Drill/drill bit for drilling out/removing caps covering pilot
screws (if not done previously)
1: If you haven't already, you'll need to expose the pilot screws.
They come from the factory covered with an Aluminum plug. Find a
drill bit that's smaller than the diameter of the cap, and
CAREFULLY drill a hole through the cap. It doesn't take much
pressure, and if you pop through the cap and the bit hits the
pilot screw, you could damage it. Once you have a hole in the cap,
you have two choices. You can either A) insert a screw into the
hole and remove the cap completely, or B) leave the cap in place
with a hole in it. I chose B, so in the pics you see here, there's
just a hole in the cap (see pic). I don't have to worry about the
screws ever falling out (I don't think they would anyway), and I
can access the screws with a small 'precision' screwdriver.
you choose A, after adjustment some people have replace the caps
with new ones from their dealer, or put a dab of silicone caulk in
the hole to cover it up. I have left mine open, with the drilled
cap in place.
Step 2: Make
sure that your carbs are synched properly (see
page). If you perform carburetor synchronization after setting
the pilot screws, you'll need to adjust them again.
Step 3: Warm
up the engine to normal operating temperature. According to the
manual, stop and go riding for 10 minutes is adequate.
service tachometer with graduations of 50 RPM or less can be used.
I bought Sears' Engine Analyzer for ~$30-$40 (see pic). While this
product is made for cars, I was able to adapt it to my bike.
REMEMBER: Don't burn yourself; the engine's hot!! (Yes...I did.)
1: Remove the seat. If you're running the stock seat, remove the
10mm acorn nut from the rear fender, and both of the 12mm (I
think) bolts from the sides of the seat, near the rear fender
rails. Then slide the tongue on the front of the seat from it's
slot, and carefully set the seat aside (see pic).
Loosen the gas tank. Remove the 12mm bolt at the rear of the tank,
and the 8mm bolt near the steering head. I was able to access the
frame neck covers and coils without having to completely remove
the tank; just having it loose was enough.
3: Remove the right side frame neck cover. The coil wire I needed
to access was easiest to get at from this side. Using a smaller
Phillips screwdriver, loosen the two plastic screws holding the
cover in place. These screws aren't actually threaded into the
frame; they expand a plastic sleeve as you tighten them. This
sleeve, when expanded, holds the neck covers in place. You'll see
what I mean when you get them off. Even with the screws loose, one
of the sleeves didn't compress on it's own, and I had to carefully
pry it out by hand. You'll need to lift the loose tank up slightly
to expose the second screw (see pic).
4: Locate the needed coil wire. The wire required for my tach to
work was the blue/yellow coil wire farthest to the right side of
the bike (closest to you once you get the right frame neck cover
off). See the arrow in the pic. Once you've found it, pull it off
the coil. It's a spade connector covered by a rubber boot.
5: Expose the spade connector. You'll have to slide the rubber
boot on the coil wire back to expose the spade connector,
otherwise once you re-attach the coil wire to the coil, there'll
be no room for the tach pickup wire. The pic here shows the boot
partially slid back on the wire. You can slide it back even
further, if necessary.
6: Attach the tach pickup to the coil/coil wire. My tach came with
an alligator clip pickup. I simply attached it to the coil
terminal, then slid the partially exposed coil wire onto what
remained of the coil terminal. Then I slid the protective cover
over the alligator clip as far as I could get it, to hopefully
prevent any arcing to nearby metal (green cover in pic).
7: Attach the tach to the battery/ground. Remove the left side
cover to expose the battery. I attached the positive tach cable to
the battery's positive terminal, and the negative cable I attached
to a ground I found under the seat (see pic). Now, the tach's good
1: Set the pilot screws to an initial setting. With the engine
off, carefully turn the pilot screws all the way in until they are
LIGHTLY seated. If you tighten them down, you'll damage the pilot
screw seats. Then, back them both out 2 1/2 turns as an initial
setting. I used a "precision" screwdriver (read: small), and on
the end of it I took a Sharpie marker and made a black dot, so I
could count the turns easier (see pic).
Because this tach was made for cars or other engines with 4, 6,
or 8 cylinders, it doesn't read exactly right on the V-Twin
Sabre. On the following pictures of readings, look at the top
line, near "RPM." You'll see it's broken down into 0-6000 RPM
(above the top line), and 0-1000 RPM (below the top line). I
used the 0-1000 RPM scale for this adjustment. Because I had it
set for a 4-cylinder motor (the lowest setting available), I had
to multiply the indicated reading by 2 to get an accurate
result. Since this tach is broken down into 20 RPM increments on
this scale, each 20 RPM increment actually indicates a 40 RPM
change, so it's still useable for this purpose.
Adjust the idle speed, if necessary, to 1000 +/- 100 RPM. Using
the tach, note the initial idle speed. At 2 1/2 turns out from
seated, my initial idle speed was about 450 X 2 = 900 RPM (see the
slightly blurry first pic). While this is technically within
specs, I adjusted it to 1000. (The needle bounces around a little,
so the second pic shows slightly over 1000 RPM.) Turn the throttle
stop screw (see arrow in third pic) to adjust the idle. The engine
can take a minute or so to fully respond to changes, so give some
time between adjustments for it to compensate.
Adjust the screws. Turn each pilot screw out 1/2 turn from the
initial setting. If the engine speed increases by 50 RPM or more,
turn each pilot screw out by successive 1/2 turn increments until
the engine speed doesn't increase. WAIT a minute or so between
each adjustment. I found that it took a bit for the engine to
respond fully to each change.
Adjust the idle speed to 1000 RPM.
5: Adjust the #1 (rear) carburetor. Turn the pilot screw on the
number 1 (rear) carburetor IN until the engine speed drops by 50
RPM (see pic). Then, turn the pilot screw OUT 3/4 turn. This is
the final opening position.
Adjust the idle speed to 1000 RPM.
Adjust the #2 (front) carburetor. Repeat steps 5 and 6 for the #2
done!! Carefully disconnect the tach and re-assemble the bike.
Make sure you press that rubber boot back down over the coil
wire/terminal. And if you moved your tank, be careful that you
don't pinch any hoses running from it when you replace it. Now
start her up and go for a ride!! See if the popping on decel is
gone. If not, you may want to try backing out the screws a little
further, or perhaps rejetting. Be careful, though, I've heard that
if you find you need to have your pilot screws backed out more
than 4 turns from lightly seated, you run the risk of the screws
coming loose, and you may lose them. Good luck!!
questions, e-mail me at