Twin carbs cables - WHY ????????????

[Iconic944ss]

After much lube-ing, routing and general fannying about with the cables on my 900ss, I have managed to get a fairly light action on the throttle.

But - WHY OH WHY - is there a return cable on the throttle when the return spring on the carbs is more than up to the task of making the slides close.

Also don't the later models have a single cable throttle ? Could this be retro-fitted to an earlier bike ??

Regards - Frank

[Felix]

The reason for a second cable to shut the throttles has to do with earlier carbs and especially carbs using slides as opposed to butterflys. Slides can easily stick open under deceleration when the engine is pulling a strong vacuum. The slides are being sucked into the engine which makes them stick. If you'd fit a return spring big enough to overcome this effect, you'd not like the stiffness of the throttle for opening.

Carbs that have butterfly throttles are far less prone to this problem and as you say the later fuel injected models which utilise butterflies only use an opening cable.

Yes, you can retrofit them to older carbs, but you have to make a judgement on the throttles potentially sticking open.

[Iconic944ss]

Cheers for that Felix, it sounded very plausible until I thought about it for a while.....

The slides have their own springs under the top cover that act directly on the top of the slide - I have to have a look at my spare set of carbs to see how the cable arrangement works on the carbs but.......the CV carbs still have butterflys in the throats (that sounds awful - :lol: ) and I think its the butterflies that are controlled by the cables while the slides and controlled by the springs and the pressure difference...does this sound right?

Regards - Frank

[Derek]

The butterflies are indeed controlled by the cable and the slides by the inlet pressure but the butterfly spindles also have a return spring. That's the one that will close the throttle if you remove closing cable.

[Felix]

The cables indeed operate butterflies on the CV carbs. My post was more to the reasons in general for dual cables. There are racing carbs (non CV) where the slides are operated via cables and these don't have butterflies. Some of this is historical and has been retained over the years for most carb setups mainly for safety reasons. It's only with the advent of fuel injection that single cables have proliferated.