AIR/FUEL MIXTURE SCREWS (a.k.a. PILOT SCREW) ADJUSTMENT

by Tom "911Medic1" Myhre

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.

You will need:

• Service Manual (page 5-18 and 5-19)
• Tachometer (capable of showing 50 RPM changes in engine speed)
• Standard (flat-head) screwdriver small enough to reach pilot screws
• Phillips screwdriver small enough to fit into frame neck cover screws
• Ratchet 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)

PREPARATIONS

Step 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. If 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.

ATTACHING THE TACHOMETER

Any 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.)
Step 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).

Step 2: 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.

Step 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).

Step 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.

Step 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.

Step 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).

Step 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 to go.

ADJUSTING THE SCREWS

Step 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).

NOTE: 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.

Step 2: 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.

Step 3: 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.

Step 4: Adjust the idle speed to 1000 RPM.

Step 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.

Step 6: Adjust the idle speed to 1000 RPM.

Step 7: Adjust the #2 (front) carburetor. Repeat steps 5 and 6 for the #2 (front) carburetor.

You're 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!!

Any questions, e-mail me at tmyhre29@hotmail.com