You are reffering to the impulse line. Yes it has to have one if the caburetor has a diaphram in it which is most likely does. This line is located between the back of the housing that secures the carburetor and the crank case. You will have two tubes. One is your tube that takes the air/gas mix to the cylinder and the other small one that looks like a fuel line goes to the crank case, this one is your impluse line. You will notice when you remove the carburetor from the saw that there is a tube on one side of the carb. that goes into the housing. not the fuel line that goes down. This line, when you put the carb. on the carb. plugs right into this line automatically. That is your impluse line. If it has ANY cracking what so ever this is mess of the vacuum that is need to pulse the diaphram.
David Trowbridge, October 2009
