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Round Slide Carburetor Synchronization How To:
Build And Use Your Own Sync Tool!
By Markus
Building the carb sync tool:
- Start with a piece of thin wood, 4 inches by 14 inches.
- Mark it with horizontal lines, every ½ inch. Seal it with polyurethane.
- Find a jar lid, (baby food or other of similar size). Using a screw, mount
it centered left/right, with the jar cover edge up, one inch up from the
bottom of the wood.
- Get a six foot piece of clear and flexible gas line from your local
dealer.
- Center it around the jar lid and mount it on the piece of wood. You can
use "GOOP" on the backside of the hose, or drill small holes and use wire to
fasten it in several places. Make sure both ends of the hose are the exact
same length.
- Fill the hose with antifreeze, (70/30 mixture), so that it is up half way
on each side of the wood, (maybe an ounce or less).
Using the carb sync tool:
Note: These instructions apply to round slide carbs. Flatslides, EFI,
butterflies and diaphragms are different.
- The purpose of synchronizing the carburetors on multi cylinder motors is
to balance the intake on each cylinder. This gives better throttle response,
a smoother idle and better mileage. On a twin, match the carburetors
together. On a triple, do two, then match the third to one of the other two.
Note: If the carburetors are way out of adjustment, you will need to do a
"rough" adjustment first. If the carbs are close, skip down to the "Fine
Tuning Adjustment" section.
Rough Tuning Adjustment:
- Remove the airbox for free access to the carburetors.
- Unscrew the idle speed screws, (big knurled knobs on the side of the
carburetors you can turn with your fingers), so they are no longer touching
the slides. You will feel the resistance change as you are turning counter
clockwise. The slides should bottom out in the carburetors. If not, the
cables may be too tight. In that case, use a wrench to loosen the locknut on
top of the carburetor, and spin in the adjuster so the slide comes all the
way down, and the cable is slightly loose.
- Adjust the idle screw in on each carburetor until it just touches the
slide. Now turn it in another four (4) turns. The carburetors are now
roughly balanced at idle. (Another way is to lift the slide, install a
pencil, turn the idle screw in till it just lifts off the pencil on each
carburetor.) The actual idle speed will need to be adjusted when the motor
is running.
- Now squeeze the throttle slightly, (just off idle is enough), and
look/feel the slide lift. Adjust the throttle cable up on the "slower"
carburetor, until they both lift at the same time. Now you are done with the
rough "off idle" adjustment.
- Next test the "freeplay". Squeeze the throttle slightly until you are just
lifting the slides. How much clearance is there on the throttle lever? The
manufacturers specify this as it affects the throttle safety switches on
many models. The width of a credit card is about right. You will need to
loosen the nut on each carburetor, and adjust in/out the same amount to get
the freeplay correct. Now go back and check the synchronization at "off
idle".
- For the final test, squeeze the throttle full on. Feel inside the
carburetors; are the slides all the way up? If not, check the throttle cable
condition, routing, and your previous adjustments. Also check for
interference with grips, thumb warmers and the like. Repeat for 3rd/4th
cylinder, then move on to fine tuning.
Fine Tuning Adjustment:
- Dig out your synchronizing tool.
- Put the sled on a stand, (very important for safety).
- Start your sled and warm it up, shut it off.
- Ensure the airbox is installed. Hook up your synchronizing tool to two
carburetors, using the port on the "engine side" of the carburetor. (The
ports will be covered with some type of rubber plug.)
Note: Some carburetors may have a smaller fitting requiring adapting. In
this case, use a couple of pieces of smaller diameter (primer type) tubing
forced inside of the carb tools larger tubing. Be careful to keep the
lengths the same and ensure an air tight fit. (See picture.)
- Start the sled but do not touch the throttle.
- Ensure the carb sync tool is level, and adjust the idle screws to balance
the antifreeze from side to side. You will need to adjust the screw on the
carburetor with the coolant at the lowest level, in a clockwise direction.
Adjust both carburetors up or down evenly to get the idle you want. Shut the
sled off, swap the synchronizing tool lines, re-start, and double check your
readings; they should read the same. (If the lines are not the exact same
length, you will get different readings, adjust your line length.) On sleds
with more than 2 cylinders, match the remaining cylinders to one of the
first two.
- Next start the sled again, and squeeze and hold the throttle to bring the
RPMs just off idle. Turn the throttle cable adjuster counter clockwise on
the carburetor with the coolant at the lowest level, to even the coolant. On
sleds with more than 2 cylinders, match the remaining cylinders to one of
the first 2.
Note: Don't let the sled idle to the point of overheating. If you adjust
idle in the summer, you will most likely have to readjust in the winter.
- That's all there is too it. Now go amaze your family and friends!
skrevet af markus1068@aol.com
Copy /pasted af : Daniel