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What is Jetting?
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Technical Advice
What is a jet? Is Piped and jetted like Bored and Stroked?

A engine needs to have Air and Fuel in the correct mix to run at top power.

The things on a moped that control the air fuel mixture are the carburetor and air box. Inside the carburetor there are holes made to an exact size that allow fuel to pass through and mix with the air. These orifices are called JETS. 

The pilot jet is a small jet for idle speed. The pilot jet air mix is adjusted with the air screw. Most air screws are set about 1 and 1/2 turns out. The slide needle is a long needle with a circlip to position it in the throttle slide. The slide needle controls fuel mixture at 1/4 to 3/4 throttle.  It is adjusted by raising or lowering the needle to control the amount of fuel that is allowed through the main jet. The main jet is for 3/4 to wide open throttle.
Here are some things that affect jet size:

-Changing air cleaner, air box will affect how much air gets to the carburetor.
-Cleaning or oiling the air filter will affect how much air can get through it.

How do I tell if I am running Rich or Lean?
When rich, (too much fuel) the engine sputters,  acts like it is cold, won't warm up, does not clean out, chugs, spark plug gets black, plug fouls, won't rev up.\ When Lean,   (Not enough fuel) Dies out, Wheezes, runs out of gas, Seizes, gets hot, spark plug is white, spark plug has little melted gobs on it,   warms up fast, you can start engine cold and rev it right up.

Why did my piston seize?
On a two cycle engine, the fuel cools the piston.  If you do not get enough fuel through to keep the piston cool, it will get too large for the hole in the cylinder and stick. If you add more oil to the fuel, that means even less fuel cools the piston and it will seize even more. If your piston sticks, that means you are running to lean. If your connecting rod sticks, THAT means you need more oil.

What can I do to experiment?
To make it lean open up the air box a bit make sure the intake boots are not shrinking down clean out the air filter remove the air box.  To make it rich: Close off the intake holes in the air cleaner box.    Hope this helps.

Scooter Therapy Inc
12 North Few Street  |  Madison, WI 53703    
toll free 1-800-411-1543  |  local 1-608-255-1520    

fax 1-608-255-1587  |  E-mail

Scooter Therapy Inc    

12 N. Few St      
Madison, WI 53703 

toll free 1-800-411-1543    
local 1-608-255-1520    
fax 1-608-255-1587    

Hours: M-F, 9-6 Saturday, 10-3  CST

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Scooter Therapy inc.