How to Stop a Motorcycle from Idling Too Low or Too High

How To Stop A Motorcycle From Idling Too Low or Too High

A motorcycle idle level rarely changes from the standard setting. If your bike is idling high or low this indicates you may have something wrong. Lets go over a few things to check that might help your motorcycle idling issues.

How To Set The Idle

Many older motorcycles that use a carburetor to mix the air and fuel, set the idle with a simple stop screw. The screw prevents the throttle valves from closing completely, allowing fuel to consistently flow into the motor when you are off of the throttle. Just simply turn the screw in or out to adjust the idle. The screw is usually located on the carburetor near the choke. This same screw system is used on the first generation of fuel injected motorcycle engines.

idle screw air screw carb top float bowl

Newer models that have fuel injection systems have an ECU (Engine Control Unit) that controls the idle level. If your bike has an ECU you cannot adjust the idle easily. If your bike is idling poorly with an ECU then this points to a larger problem than simply adjusting your idle with a stop screw. My recommendation would be to take it to a shop and have it tuned by a professional.

ECU mapping idle high or low

A motorcycle idle is usually set between 1000 and 1500 RPM when the engine has reached it’s operating temperature. While the bike is warming up the RPM can be a little higher than at operating temperature. The best idle speed really depends on the type of engine and air to fuel ratio. The best thing you can do to figure out what idle speed is best for your bike, is to search in the user manual. If you don’t have a physical copy, most can be googled and obtained digitally. 

There is risk for running the motorcycle idle too low. This can cause low oil pressure and is a real risk. If you aren’t going to set your idle to the factory level then you should always aim for high idle speed over lower. 

Motorcycle Idle Too Low

If your bike has been warmed up and is idling lower than the recommended level from the manufacturer, you probably have a couple of problems:

  1.  The engine will stall easily or may not stay running without throttle being added. You will also experience stalling during take offs.
  2. The oil pressure in the engine will be very low

Here are some potential causes of those problems:

  • Idle Screw isn’t set properly or the ECU isn’t setup correctly. This is usually the first thing people check.
  • Too Lean Air to Fuel Ratio – stock bikes usually run slightly lean so if you do any modifications such as change the exhaust or air filter. This could result in more air flow than the stock parts and cause the motorcycle to run too lean. Check out my article on backfires that might answer some of your questions about air to fuel ratios.
  • Valves have too tight of a clearance.
  • Throttle Valves are not synced properly.
  • (TPS) Throttle Position Sensor is not adjusted properly.
  • Fuel tank Charcoal Canister is clogged by dirt or old fuel and isn’t allowing enough fuel to the carburetor.

Motorcycle Idle Too High

A motorcycle idle that is a little high is not dangerous for your bike but isn’t optimal either. However, if your bike is revving out, you should shut if off and attempt to resolve the issue or you could blow up the motor. 

When your idle is high these are usually the problems you come across:

  • Louder than usual noise from the motor winding up to higher RPM.
  • You may hear a loud grind sound when you put the bike into gear because the RPM are too high even when you are off the throttle.

Here are some of the probable causes of your high RPM. 

  • Idle Screw isn’t set properly or the ECU isn’t setup correctly. This is usually the first thing people check.
  • Your Oil Temperature Sensor or Water Temperature Sensor has gone bad.
  • Your throttle valves are not synced properly.
  • (TPS) Throttle Position Sensor is not adjusted properly.
  • Throttle Cable is jammed and will not allow the valves to close.
  • Cold Start Lever Cable is jammed and the valves cannot close.
  • You have a leak in your Intake Rubber Hoses which are between the cylinder head and the throttle valve housing.

If you haven’t noticed most of the problems causing high or low idle are the same for both issues. 

Keep your air filter clean and don’t run bad gas. These are things that can lead to or cause idle issues. If your air filter is dirty then there will be dirt particles that will go through it and find their way into your injection system. Over time this could build up and cause a clog and you will find yourself spending a lot more time working on your bike than the time it takes to just clean the filter regularly. Regular maintenance is a huge part of being a rider and should become routine for you. 

Check out my article on How To Start Your Motorcycle If It’s Been Flooded With Water.