Basic knowledge for motorcycle parts: Carburetor

by Goldie 17. March 2011 05:55

If we’ll run through previous blog posts, we’ll notice that many of motorcycle parts issues are more or less connected to carburetor’s work.  Carburetor is known as pretty vital motorcycle part.  The engine without carburetor, would not work. Let us explain what actually carburetor does for our motorcycle in next paragraph.

simple carburetorToday we won’t bother you with modern motorcycle carburetor but with the simplest one that have been around for quite a while. In the picture you’ll see a carburetor on a spark ignition engine which is not the same as motorcycle with diesel engine. The main difference between carburetor on a spark ignition engine and carburetor on a diesel engine is that the first one controls the engine speed by throttling the amount of air send to the engine (carburetor on a diesel engine doesn’t work with air throttling).

The main motorcycle parts of spark ignition engine carburetor are:

Fuel bowl. This motorcycle part provides a source of fuel. It’s like one big dish with fuel where the air pressure over the fuel is equal to the normal atmospheric pressure level. Regulation of the air pressure in the fuel bowl is done by the fuel bowl vent- basic carburetor’s part.

Venturi. This part is portion of the carburetor’s main air passage that momentarily narrows down. How venturi accelerate air coming into the engine?  Some guy called Venturi found out that if you took passageway like a tube, and narrowed it down just a bit in the middle, the air flowing through it would have to accelerate as it went through the narrowed down portion. It would then return to its normal speed at the other side of the tube where things open up again.

Fuel jet. This motorcycle part is connection between the Fuel bowl and the Venturi motorcycle part. How the fuel comes from the bowl to the venturi? Well, pretty much simple pressure technique: As the airflow in the venture accelerates its pressure drops below normal surrounding atmospheric pressure, but the air pressure in the fuel bowl is still at normal atmospheric level and the difference between the two is what draws the fuel up through the jet passage.

Throttle butterfly. Some carburetors have throttle butterfly part. This motorcycle part is there to control the amount of air going into the engine. The stationery engines have a fixed rate carburetor and don’t vary the amount of airflow.

In the upcoming blog posts we’ll get to know more complex carburetors and other main motorcycle parts.

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New motorcycle parts needed around your carburetor or not?

by Goldie 5. March 2011 04:23


Have you ever wondered what’s wrong with your carburetor? Have you ever asked yourself why fuel is coming out of the air jet? And why your good old motorcycle isn’t running?.

 The problem can be solved with simple replacement of one tiny motorcycle part or cleaning of the carburetor. But let’s see what possible situations here are:


  • If the reason for not running of your motorcycle is the carburetor (in this blog post we’ll only talk about carburetor issue connected to not responsive motorcycle) check all jets, passageways and float needle. Why checking the float needle? Well, simple the float needle mustn’t leak when float is raised.  If the needle is not responding, the time is now for new motorcycle part – float needle.
  • Other thing you haven’t figured out is the possible rubber diaphragms on the carburetor (not all motorcycles have it). These small motorcycle parts should not have any pinholes in them.
  • The carburetor is attached to the engine via air jets. Use carburetor cleaner spray to check if there are any air leaks. If the engine speed changes than you have an air leak.  
  • We are not going to write about carburetor cleaning here, the previous blog post for cleaning main motorcycle parts explains carburetor cleaning more in details.

To sum up- for making your motorcycle run - check the fuel, the carburetor, the spark plugs and all connections/ jets in between.