When do you know when to replace the cush drive rubbers?
The previous owner may have noticed a change, possibly the primary transmission was getting a little harsh when going from drive to overrun or vice versa?
Or maybe he had inspected them and found they were getting soft? Sometimes small pieces of rubber can be found in the bottom of the primary case when rubbers begin to break up.
Have you noticed any jerkiness in the primary transmission when rolling the throttle on or off?
If not then there may be nothing much to worry about, although if the rubbers are original they are over 30 years old and could probably be overdue for replacement?
I only tried balancing the carbs by taking the plugs off alternatively
and adjusting the air regulating screw and throttle stop screw.
Removing each plug in turn is one way to set the throttle stops (but removing plug caps with the engine running is not really recommended if you have an electronic ignition system fitted as it could eventually damage the ignition unit or coils) and the pilot mixture would normally be set by turning the pilot screws to give the most even running on each cylinder.
The throttle slides also need to be synchronised using the cable adjusters on top of the carbs.
I am wholly ignorant of vacuum gauges, they sound more accurate,
I would be interested to know how they work?
Vacuum gauges generally give a visual indication of the throttle positions, so by setting the vacuum readings to read equally for both carbs both throttles can be accurately synchronised for lift and throttle stop positions, and you can immediately see any changes in vacuum as you make the adjustments. The gauges are connected between the carb throttle and the cylinder head by rubber pipes, sometimes it is necessary to drill and tap a connection for the pipe adaptor in the inlet somewhere although many modern bikes have these as standard but on a Bonneville the balance pipe can be temporarily removed and the pipe stubs used as the vacuum connections.
I use a Morgan Carbtune (4 cyl.) rod/tube type balancer
http://www.carbtune.com/index.html although there are various different types available (gauge and electronic etc.).
T
he air regulating screws are: left 3 stops, right about 5.
Not sure what you mean by "stops"? Normally I would expect the (Amal Mk1) carb screws to be set around 1.1/2 turns out?
I generally test the carbs by running the bike to work (8 miles) so it goes through many throttle positions, should I be trying just one setting at a time?
If the bike is running OK then there may be nothing much wrong? However if there is a problem where one carb is constantly rich (black sooty smoke? sooty plug?) then maybe the carbs need to be cleaned and the float heights checked, and check the floats are not sticking and that petrol has not got inside them as the floats are hollow and the seams can split?
Here is some carb info you may find useful:
http://www.jba.bc.ca/Bushmans%20Carb%20Tuning.html
