Pressure testing of fuel system/carb

[thompson1600]

When you pressure test the carb, do you close the H and L or leave them open at their basic setting? Should the carb hold pressure without any loss or pressure? (in most of the other components Stihl says it can hold for 20 seconds and lose a small amount and still be ok).

What are the most common areas that make a carb NOT reuseable for a rebuild kit?

Thanks

Tom

 

[stihltech]

pressure

Pump up to about 1/3 to 1/2 guage. It should hold perfect. Press on the diaphragm with a tag wire, it should pass air and the shut off and hold steady. Close both needles, open one at a time, and press on the diaphragm with a tag wire. Air should pass through both needles somewhat equally and at a pretty good rate.
The first test checks for leakage past the inlet needle. A worn needle, dirty or pitted seat, wreak spring, or a binding lever will cause leakage.
The second test verifies the passages are open. any blockage will slow the drop of air.
I also use soap and water around the outside to look for leaking gaskets, and in the venturi to check the brass valve jet. The jet will also cause a stall at idle.

 

[JimL]

Pump up to about 1/3 to 1/2 guage. It should hold perfect. Press on the diaphragm with a tag wire, it should pass air and the shut off and hold steady. Close both needles, open one at a time, and press on the diaphragm with a tag wire. Air should pass through both needles somewhat equally and at a pretty good rate.
The first test checks for leakage past the inlet needle. A worn needle, dirty or pitted seat, wreak spring, or a binding lever will cause leakage.
The second test verifies the passages are open. any blockage will slow the drop of air.
I also use soap and water around the outside to look for leaking gaskets, and in the venturi to check the brass valve jet. The jet will also cause a stall at idle.

you pretty much summed that up.

 

[thompson1600]

What is a tag wire?

In the first test you have the carb together and are pressure testing it from the fuel intake I assume.

In the second test you have the carb apart and are pressing on the diagphram to see if air is coming out of the H and L holes I assume?

Thanks

Tom

 

[stihltech]

testing

All testing is done with the carburetor assembled.
A tag wire is the small wire on a repair tag. Bend the end up slightly so when you slide it in the vent hole on the metering diaphragm cover, it does not puncture the diaphraghm, like I did the first time.
Use the wire to depress the diaphragm to open the inlet needle.
With both needles closed, if air passes, you may have a leaking welch plug.

 

[Ax-man]

A small rubber coated paper clip with one side bent straight out works good, too.

Larry