Adjust throttle free play

Free play is the small amount the twist grip turns before the cable starts to open the throttle. With too little, the idle rises when you turn the bars and the throttle may not close fully. With too much, the bike feels slow to respond and jerky. Check it at every service.

Safety

• The throttle must snap shut by itself from any position, with the bars straight and at full lock. If it does not, do not ride: see Throttle sticks or does not snap shut.
• If you run the engine to check, do it outside, in neutral, on the stand, and keep clear of the hot exhaust.

You need

• Two small spanners for the adjuster and locknut, a ruler.
• Your bike's value. K-Light 125: 3 to 5 mm at the grip flange. For other bikes use the manual.
• On a carburettor bike, set the idle speed first (Adjust carburettor idle speed and mixture). On a fuel-injected bike the ECU controls idle.

Steps

1. Bars straight, engine off. Turn the grip gently until you feel the cable start to pull. Measure how far a point on the grip flange moved. That is the free play.
2. If it is outside the value, find the adjuster at the grip end of the cable: a threaded barrel with a locknut, often under a rubber boot.
3. Loosen the locknut. Turn the barrel a little and measure again. One direction increases play, the other reduces it: watch the gap change.
4. When the play is right, hold the barrel and tighten the locknut. Refit the boot.
5. If the grip adjuster runs out of thread, set it to the middle and use the adjuster at the carburettor or throttle body end for the big change. Then fine-tune at the grip. Leave the grip adjuster with room both ways so the rider can adjust later.
6. Bikes with two cables (one pulls open, one pulls closed): set free play on the opening cable. Set the closing cable as the manual says, never tight.
7. Start the engine. At idle, turn the bars to full left and full right. The idle must not rise. If it rises, the cable is too tight or routed wrongly.

Check your work

• Free play is within the value at the grip.
• Idle does not change at full lock.
• The grip snaps shut from full open with the bars straight and at each lock.

If it did not fix the problem

• Grip is stiff or slow to return: Lubricate or replace the throttle cable.
• Idle stays high with correct play: Idle speed is too high.
• Electric bikes use a twist-grip sensor with no cable: see Power cuts in and out with the throttle.

Reference values (K-Light 125)