Carburetor Synchronization (Carb Sync)

[berserker789]

I'm trying to sync my carbs since the last time I took my carburetors out and cleaned them, I changed the tension cable and now have to re-adjust them.

The idle sync is simple enough. I adjusted the sync cable when idling around 1200 rpm and the vacuum pressure is pretty equal.

However, I'm confused when it comes to the high rpm sync. When I was adjusting the throttle cable initially without the carb sync tool, I was basically just trying to get the throttle bodies to open at the same time when I pull the throttle. However, if I have to adjust just the front carb throttle cable to adjust the high rpm carbs, that changes the rate at which the throttle bodies open.

Also, when I adjusted the front throttle body, I couldn't get the vacuum guage to be equal no matter which way I adjusted the throttle cable on the front carb. The vacuum needles would actually go the opposite way when I hold the rpm high.

What am I missing here?

[Lechy]

Have a look here:
http://intruders-alert.com/viewtopic.php?f=32&t=4139

[navigator]

First, make sure you have 1/8" of freeplay at the throttle grip.
Second, adjust the sync cable so that both carbs butterfly plates start to open at exactly the same time.
Third, adjust your A/F screws.....instructions below.
Forth, you will need a manometer (sync tool) to perform the sync, either home made or bought.

A/F adjustment
1. Make sure you have about 1/8" of free play at the throttle grip.
2. Motor off,Gently seat each A/F screw and set both A/F screws 2-1/2 turns out
3. Engine running at operating temp, lower your idle to about 800 using the thumbscrew on the rear carb.
4. Engine running at operating temp, turn an A/F screw CCW until the motor starts to stumble, Then screw CW until the motor starts to stumble again, count the number of turns between, then screw CCW to achieve the best idle...about 1/2 way between stumble points.
5. Repeat on the other carb.

Now sync:
1. Remove screw near each manifold, install sync tool. (don't lose the fiber washers)
2. Raise idle to 1000 rpm with thumb screw.
3. Remove gas tank and hook up an aux. fuel source.
4. Engine running at operating temp, adjust the idle sync cable to balance carbs using sync tool. (rear cable on front carb)
5. Using the throttle grip, raise the rpms and hold them constant, any rpm will do between 2000 and 3000 rpm.
6.Adjust the throttle cable to balance carbs using sync tool. (front cable on front carb)

Presto!
7. Remove sync tool and replace screws and fiber washers.
8. install gas tank.
9. Test ride and smile.
You may want to blow a fan on the engine, it can get quite hot.
Make very small adjustments, and tighten each locknut when done.

[berserker789]

Alright, I managed to sync the carbs and the idle. Both high rpm and idle are showing the same vacuum points on the carb sync tool. It was a PITA. I think the throttle cables have been replaced at some point and the throttle cable to the rear is a tad too short IMO. I loosed it completely at the rear carb and still had to loosen it at the handle bars at the max amount just to have some free play. I had to adjust the front carb to match the rear since the rear throttle body would open up first.

I did not adjust the A/F ratio. Where are those screws located?

[navigator]

On the side of each carb is a buried screw that looks like this:



It may have a solid brass plug covering it, with a small hole in the center. Carefully put a sheetrock screw in that hole, and wiggle the plug out with vice grips.
Carefully seat the screw counting the number of turns on each.

Skip to the bottom of this thread for the A/F video:
http://www.intruders-alert.com/viewtopi ... =32&t=4139

[hillsy]

Squirt a bit of penetrating oil on the idle mixture screws before you try and turn them in - very easy to munt the threads on these if they haven't been touched for a decade or more.

[Lechy]