Adjust Throttle Cables

Adjusting cables while somewhat simple in terms of mechanical tasks, is often not a simple operation when you look at all the adjustments. What? There’s more than one thing to adjust?

Throttle cables:

All bikes come with a push and pull throttle cable system. The pull is obvious to allow fuel to get to the engine in increasing amounts allowing the bike to accelerate by twisting the throttle.  The push cable makes sure that the fuel decreases to slow the bike down and is also there for safety in that it mechanically forces the throttle bodies or carbs to reduce fuel into the cylinder.

At the throttle housing section on the bar sometimes both cables have adjustment, sometimes only one. The same applies on the throttle body or carb end too. One or both have adjustment; so where do you start?

The most obvious place to start is at the bar end. Look at your cables and see which one has the adjustment. Normally you will see an exposed adjuster of a hex shaped cylinder and a lock nut or a nylon cylinder and lock ring. Other cables have a rubber sleeve hiding/protecting the adjuster.

Throttle cable covered

Throttle cable adjustment uncovered

The first test is to use only finger and thumb and see how much free play you have in the throttle cables. Can you get an 1/8 or more of a turn? Is it more or less than that. You “feel” free play with very light movement. Therefore if there’s no movement, there’s no free play.

How much free play should there be? That’s a personal decision for each and every one of you. You can go from zero free play to a maximum of 1/8 of a turn. Any more than that and you are substantially increasing the amount of rotation the throttle grip (therefore your wrist) goes through!

Most throttle tubes range from a 1/4 turn to a 1/3 of a turn. The less rotation you have the quicker the fuel gets to the engine – so what amount of rotation do you have? Go on, get out to your bike and check it!

Welcome back – now you know what you have. Did you check for free play as well? Do you have adjusters at the bar end of the cable? What type? Yes you guessed it, get back out there to the bike………

Now you know what you have for rotation and free play which are essential in knowing what you are dealing with.

The adjusters at the bar end give you a limited range of adjustment. Like a chain, the cable will stretch over time hence the need to take up the evolving free play as the cable ages. Now go back to the adjuster(s), remove the lock ring or nut and move the adjuster to see which direction gives you more free play or less. Now that you understand how the mechanism works, move the adjuster until there is no free play in the cable, then back it off slightly. Remember, no more then an 1/8th of a turn of free play.  Once you have decided on what feels best to you, lock the adjuster in position with the lock ring or nut. Sit on the bike, stand it upright and work the throttle back and forth – does it feel okay in terms of the amount of travel your wrist goes through? Would you like less rotation? Put the bike back on the kickstand and take free play out of the cable. Go through the same process again until you are happy with the adjustment.

I can’t get all the free play out of the cable – HELP!

Obviously not the same bike as above. An example of the "easy" throttle body to reach.

If that is the case, you are in for a lot more work. Sometimes the throttle bodies and cables are easy to access, other times you have to invest 2 to 3 hours to get the job done depending on where the cables are routed. If they are on the end of the throttle bodies or carbs, they are usually easily accessed. If they are in the middle, that normally requires removal of the tank, air box and electrical to get to the cables (ask CBR600 owners how much work this is!).

If you are going this far into the job you need to follow these steps:

  1. Put the bar end cable adjusters at their minimum setting
  2. Get an owners manual and follow the instructions precisely OR
  3. Hold an impromptu social gathering and get concensus on the process going through 1 and 2 and get the job done

You can of course take the bike in to have a professional make the adjustments if the cables are hidden under the air box but honestly it isn’t that hard.

A word of warning here if you are going to do the job yourself.

When adjusting the cables on the throttle bodies/carbs you can over adjust leaving the slides open and fuel going into the engine rather than being fully closed. Once you have made the adjustment, there should be free play at the throttle. If there’s no free play, go back and adjust the cables until you have it!

DON’T MISS THIS CRITICAL STEP!

The acid test is firing up the bike – does it idle at the correct rpm? If you turn the bars to full lock left and right, does the idle remain the same? If the idle rises, the cables are too tight so start over.  Don’t make exceptions and be lazy. Do the job right as the consequences are all very negative!

If you had the work done at a shop, perform this test before you pay for the work done.

How often should I check free play?

In general terms, every time you get on the bike. Why? A cable may start to fray (where the winding starts to break) and suddenly there’s more free play or notchy throttle operation. We  should all spend 5 minutes checking the basics!

The Author:

Dave Moss is the Founder of Catalyst Reaction and Host of OnTheThrottle video programming specializing in technical analysis and how-to segments. He has been working with street, track and race riders and motorcycle suspension and chassis geometry since 1995 and has become an internationally recognized authority in his field through his work with regard to testing and tuning. Dave is an avid rider and races with AFM in Northern California and is the 2011 450 Superbike Class Champion.

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