Build your own throttle sync tool for 4 bucks.
Found this on the web. It was aimed at carbs but can be used for throttle sync.
Essentially it's a differential manometer and looks to be very accurate for balancing vacuum.
You may need to get vacuum tips for the ports to connect to and maybe a couple of restrictors.
Here's the Materials List for the $4 Carb Synchronizer Tool:
•20 feet of clear plastic (vinyl) tubing - inside diameter big enough to slip on the vacuum nipple of your carb (3/16" i.d. worked for my bike, but it's tight, maybe 1/4" i.d. might be better). 15 cents per foot in the plumbing section at my local 'big box' hardware store, Sutherlands.
•A yard stick - Home Depot sells an aluminum yardstick for under $2, but you can make a perfectly satisfactory gauge with a 3-foot piece of 1" wooden lathe for next-to-nothing. (For a 'professional'-looking gauge, I actually used a yellow aluminum 4-foot rule, but that was wretched excess at $5.)
•3M/Scotch/Whatever - clear mailing/packaging tape. You should have some of this left over from the Christmas mailing season; otherwise around a $1 a small roll (and you won't need much).
•2 short nylon zip-ties - You should have these in your garage. If not, buy them in bulk for cheap in the wiring section of Home Depot, Sutherlands, Ace Hardware, etc. - you'll use them and wonder why you didn't have them before.
•A tiny amount of automatic transmission fluid - Actually, just about any fluid works, including used motor oil, colored water, 2-stroke oil, etc. I chose ATF because I already had a gallon of it and (most important) it is really thin and is RED (which looks WAY cool as the indicator fluid against my fancy yellow ruler) and ATF won't hurt the engine if it accidentally gets sucked in the carb's vacuum port.
Building the Balancer
Fold your 20' of vinyl tubing in half and mark the center point. Lay your yardstick down flat on a convenient work surface (kitchen table or floor). Place the center point of the tubing at the bottom end of your yardstick (there is generally a hole at the top end of the yardstick - put the center-bend of your vinyl tubing at the opposite end of the yardstick from that hole). Carefully run the tubing up each side of the yardstick, making sure that the tubing makes a smooth, non-kinked bend at the bottom.
Use the clear packing/mailing tape to fasten the tubing in place on either side ( left and right ) of the yardstick. Thread the zip-ties through the hole at the top of the yardstick and snug the left and right side tubing to the respective sides of the 'stick with the zip-ties. You should now be able to hang your yardstick from the hole in the top ( I use a bungee suspended from a hook in the garage ceiling). The tubing runs around the perimeter of the yardstick and about seven feet of tubing hangs down from the left and right sides of the 'stick. I fold a piece of tape around each end of the tubing like a little flag and mark the left side with an "L" and the right side with an "R" using a magic marker.
Now, put one side of the tubing in the container of automatic transmission fluid and, using the other side of the tubing like a drinking straw, suck ATF fluid about three feet up into the tubing. Maintaining suction for a second, pull the tubing out of the ATF container and then raise BOTH ends of the tubing above the top of the yard stick. Temporarily fasten both ends of the tubing high enough that the ATF drains down to the loop at the bottom of the yardstick. I recommend leaving it overnight so that all the bubbles, etc. work their way out.
Once the ATF has settled into the bottom of the tubing, the balancer is almost ready to use. If everything has gone according to plan, you should now have a nicely graduated rule hanging from the ceiling with a thermometer-like tube running up both sides, with the red "thermometer" fluid about half-way up each side at identical heights. Cut a piece of black electrical tape just long enough to cover the width of your ruler and use it to mark the height of the fluid. Your super-accurate Carb Synchronizing Tool is now ready to use.
It looks something like this
Part number for a restrictor = Dorman 47303 for about a buck each.