Carb Tuning At Dragon Motorbikes

Carb Tuning
Bike Carbs

Carb Tuning ? How Does it All work then ? –  Carburetors are relatively simple devices. Their primary function is to deliver the correct amount of fuel/air mixture at a given throttle opening (as selected by the rider). However, as with all mechanical devices, carburetors will wear over time and will also require periodic tuning and service and Dragon Motorbikes has the experience to get you back on the road.

Ever had your bike fail to start?

How about it will only run with the choke on?

These, and other common problems, are typically caused by incorrectly adjusted, broken or gummed up carbs. In most cases it is relatively easy to fix the problems with Carb Tuning and a basic set of hand tools. However, first a word of caution.

Working on motorcycles in general and carburetors in particular, can be dangerous, both during the work and after when riding the machine.

Carburetor problems and Carb Tuning  generally fall into three areas: rich mixture, lean mixture, and incorrect adjustment. Diagnosing carburetor problems is relatively easy and follows some telltale symptoms.


1) Rich Mixture means the carburetor is delivering too much gasoline. Typical symptoms of a rich mixture are:

Poor fuel economy
Sluggish acceleration
Choke not needed from cold starts
Sooty or black spark plugs
Sooty or black muffler end pipes
Strong smell of gasoline when machine is at idle
Uneven running (will often slow from regular idle rpm’s and stop)

2) Lean Mixtures means the carburetor is delivering too much air. Typical symptoms of a lean mixture are:

Backfires as the throttle is closed (primarily during coast-downs)
Lurching acceleration
White or light grey spark plugs
Requires excessive amounts of choke to run/start
White or light grey muffler end pipes
Bluing (on chrome systems) of the exhaust header down-pipes

Carb Tuning
Bike carb 1

3) Incorrect Adjustment applies to carburetors that have incorrect adjustment of the air/fuel screw and the balance between two or more carburetors – where fitted.

Incorrect adjustment can produce any of the previously noted symptoms. On multi-cylinder machines, with separate carburetors for each cylinder, the following symptoms are typical of an adjustment problem:

Poor overall performance
Rattling sounds from the clutch
Engine tends to stall easily
Erratic acceleration
Poor fuel economy
Misfires and/or backfires

Correcting Carburetor Problems

Lean Mixtures: This condition is generally caused by the owner fitting after-market accessories such as exhaust systems, air filter systems or replacement carburetors of a different type or size. In addition, if the fuel level in the float chamber is set too low, insufficient fuel will be drawn through the main jet. Some carburettors have a slow speed fuel adjusting screw that regulates the fuel/air mixture in the lower rpm range.

If no changes have been made to the bike, and it previously ran well, a lean mixture can be traced to a leaking inlet manifold or leaking exhaust (often at the interface of header pipe and cylinder head).

Rich Mixtures: This condition is primarily caused by dirty air filters, but it could also result from the owner fitting replacement exhausts and/or carburettor systems. If the fuel level is set too high in the float chamber, a rich mixture will result.

Incorrect Carburettor Adjustment: This situation is mostly caused by poor maintenance. With the inherent vibration of all engines, carburettor parts (primarily adjusting screws) tend to rotate, and therefore change their positions. Low-speed running jets and multi-cylinder balancing screws are the items most prone to self-adjust during normal operation and often require periodic corrections.

Carb Tuning – It’s a black art and very easy to get wrong or make matters worse. Dragon Motorbikes will tune your bikes carbs on our dyno to get the optimum performance from your bike…that’s not just peak power its also throttle response etc.