Analysis and Solution on Typical Carburetor Malfunction (2)

  • Oil leakage

There are two kinds of oil leakage:

1.Rapid leak.

Overflow tube leak quickly, sometimes up balance tube also leak quickly which cause the fuel flow into the engine combustion chamber and the vehicle can’t start.

The cause are as follows:

1.1 There is some big dirt stuck in float bowl.

1.2 Float oil leak.

1.3 Float can’t move smoothly at the float pin.

The solution is:

Clean float needle and feeding pipe, if the float is damaged, then replace it. Or weld it after clean out the oil inside the float.

2.Slow leak

There is a drop of leaking per several minutes after parking the motorcycle for hours. The cause of the problem is that float or float needle is damaged so the seal is poor.

The solution is:

Replace qualified float needle and its component. If the problem still cannot be solved, then you can repair it with float needle restorer.

  • Smoke fault

The motorcycle carburetor is like the stomach of motorcycle, whether the absorption is good mainly depends on the stomach. So smoke is a kind of indigestion, like people have diarrhea. The main reason is that mixture is too thick, the fuel consumption will be larger due to the black smoke, and it will also easily damage the rectifier regulator and influent speedup.
There are two kinds of smoke fault.

1. Idling smoke

There is large amount of smoke when idling, the exhaust noise is dull and you need to step on the gas to start.

The causes are:

1.1 The idle orifice is too large.

1.2 The oil level of float chamber is too high.

1.3 The start enriching valve is not closed.

1.4 There is a big clearance between oil needle and main nozzle.

The resolution:

A: Change a smaller idling jet.

B: Adjust the height of the float, put oil level on 2/5 of the float chamber, which is the

normal oil level. Please note that when opening the cover to observe the oil level,  the carburetor must remain stand, in case the fuel spill out which will cause the inaccurate judgment of the oil level.

C: There are three kind of starting enriching valve: the manual plunger valve, vacuum plunger valve and electric plunger valve. The manual plunger valve can be repaired easier, by cleaning the plunger or replacing the spring or wire. For the vacuum plunger valve, you need to check if there is any damage or leak of the valve or vacuum diaphragm. For the electric plunger valve, it is generally the fault of electric heating unit or supply line, then you need to replace the electric heating unit.

D: If there is a large clearance between oil needle and main nozzle, new parts like chain and sprocket should be replaced.

2. High-speed smoke

There is plenty of black smoke when the revolving speed of motorcycle reach four or five thousand, which shows the obvious deficiencies of the motorcycle at a high speed.

The cause:

2.1 There is congestion at air filter or inlet channel.

2.2 The area of main orifice is too large.

2.3 The clearance between main nozzle and oil needle is a too large.

2.4 The oil level is too high.

The solution:

A Clean air filter or replace paprt cartridge.

B Replace a smaller main orifice.


Hope these will help you know more about your motorcycle carburetor.

Thanks for your time and attention to motorcycle accessories.

Leave a Reply