Most motorcycle problems are caused by the nut that connects the handlebars to the saddle.

Carburettor Synchronisation


Posts : 439
Location : Sheffield, UK

Carburettor Synchronisation  Empty Carburettor Synchronisation

Post by spitonyourgrave22 on Sat 30 Oct 2010, 5:01 am

It's not essential to synchronise the carbs at every service, but it is a good idea especially if you've changed the plugs or air filter. Keeping them balanced will reduce vibes, smooth out the idle and increase power. It should be done last. You will need a double (or quadruple) vacuum gauge. Morgan Carbtunes are good, but if you don't want to shell out £50 you might be able to hire one from your local garage.
The CB is a twin so the adjustment is very easy and unless you are a slow worker you don't need a temporary fuel supply -- the fuel remaining in the carb float bowls will keep the bike running for several minutes. If does stall, you will need to reconnect the tank (just the fuel and vac hose) and run the bike for 30 secs to refill the carbs then try again.

1.Put bike on the center stand, and start her up
2.Increase the idle speed to about 2.5k by turning the yellow plastic knob that hides between the carbs
3.Let the bike get really well warmed up (half way up temp gauge)
4.Meanwhile remove the seat and side panels, and on naked models, the rad shrouds.
5.Stop the engine and remove the tank:
6.Turn off fuel tap and detach the fuel hose, catching any spills
7.Detatch the small fuel tap vac hose from the left inlet manifold
8.Remove the bolt at back of the tank, and on S models remove the two allen bolts securing the front of the tank to the fairing.
9.Lift rear of tank slightly and detatch the two drain hoses at the rear right.
10.Carefully lift the tank clear of the bike. Gently place it on a level surface.
11.Connect the number one hose of your vac gauges to the small stub on the left inlet manifold, where the fuel tap vac hose was.
12.Remove the blanking screw in the equivalent place on the right inlet manifold and use an appropriate screw-in adapter to connect the number two vac gauge hose. Make sure they both fit tightly.
13.Squint down between the carbs from above, and you can just see a horizontal bar between them with the throttle springs wrapped round it, and in the middle of, near where the throttle cable connect, there is a small cross-head screw facing up. This is the balancing screw. Practice getting to it with a screwdriver onto it until you can do it quickly.
14.Start her up. From this point you need to work fast.
15.Let the gauges stabilise. If they give the same reading already, lucky you, you're done.
If not, turn the balancing screw a quarter turn in a random direction, rev the bike a bit then let the gauges stabilize.

Better? If not turn the balancing screw half a turn the other way, rev, and check again...
Keep fiddling with screw, revving the bike and checking the gauges until they give the same reading, or as close as you can get.
Remove the gauges, replace the blanking screw, tank (be careful to securely connect all four hoses), panels and seat.
Set the idle speed to 1300 rpm and give yourself a pat on the back!
It might sound complicated but it only takes ten minutes once you get the knack.

    Current date/time is Wed 26 Jun 2019, 8:51 pm