Determine correct Throttle cable length?

I just solved a problem where, on successful kick, my 74 Norton Commando 850 would be running at between 4-5K RPM. Turned out the cable adjustment was somehow moved, not sure how, but so it goes.
The throttle adjustment, which is located about 3 inches from the throttle grip, seems -extremely- temperamental. Moving the adjustment nut eve a little has a -dramatic- effect on the idle speed. Perhaps this is normal, but I found this to be alarming. In fact, simply -moving- the cable was actually increasing the idle speed, as if I was opening the throttle via the hand-grip.
Here's a pic of my cable / adjuster set-up.


The problem has led me to believe that perhaps the Throttle Cable that is installed on my bike is not the correct length - and I want to make necessary corrections.
I found a site, http://www.rockypointcycle.com/c-norton ... _kits.html, that lists three lengths of cable for my bike - and to be honest I have NO idea how to choose the best/correct one.
35" Cable - For Nortons with Euro handlebars
40" Cable - For Nortons with US handlebars
45" Cable - For Nortons (no further description available on the site).

I don't know how to tell if I have the Euro or American handlebars, and my manual shows various styles for each - but, here's a picture:


I have not measured the cable that is in place, but will happily do so if somebody suspects that the information would be of use - I really just wanted to know if somebody knew which cable length I -should- use ... and if anybody has some good info about a particular make/brand/vendor of the correct cable - I'm open to suggestions.

If your cable adjuster has any effect on the idle speed, the cable is set up wrong. There should be slack in the cable when the throttle grip is closed. You'll need to pull the tank and check the cable from throttle grip to carb tops to see if you can make use of the cable you have. First I'd see if you can get slack in the cable by closing up the adjuster just downstream from the throttle grip. If you can't get slack there, you'll have to see if you can get any by adjusting the screws on the carb top. If you can't get slack through either or both of these methods, you definitely have the wrong throttle cable. Once you have the throttle cable set up you'll probably have to adjust your idle speed with the slanted screws in the carb body.

gardenzombie said:

I don't know how to tell if I have the Euro or American handlebars

Click to expand...

The handlebars are Euro style, which are normally approximately 26" wide. The throttle cable seems sufficiently long enough for its length not to be the cause of the problem.