SANLI CS 3740 Petrol Chainsaw

[David_chainsaw]

Hello can someone please help i did a carb rebuild and new fuel lines tryed to test it today but i can't get it too prime i.e primer bulb not filling with fuel and im sure when i try it i hear air but can't find any leaks and all lines i on

[GardenKit]

If its a remote pump, rather than on the carb, then have you put the pipes on the right way round. Take the pipes off and operate the pump, you will find if its working and which is in, and which is out.

[David_chainsaw]

yes they are on the right way but one of the pipes seems to want to come off like its got air behind it

[GardenKit]

Most 'primers' are actually 'air purge pumps'

 

When the bulb is sqeezed it forces air past a valve and back to the tank. When released it forms a vacuum which pulls down the metering valve in the carb allowing fuel to be drawn up the pickup hose and through the fuel pump into the metering chamber. Keep pumping and all air will be replaced by petrol, and petrol will return to tank.

 

For a purge pump not to work there must be an air leak allowing air into the system rather than fuel.

 

This cold be in the pickup hose walls, metering diaphragm or nozzle check valves. Could also be that the pump diaphragm is leaking.

 

As you have just rebuilt the carb I suspect that the gaskets and diaphragms have been incorrectly assembled or the metering arm is too low to be operated by the diaphragm.

 

If a pipe is being pushed off the primer, it can only be by pressure and this should not be possible as the pressure side returns to tank. Are you sure that you are not trying to push fuel into the carb rather than pull fuel out. (pipes wrong way round)