Pressure leaking from Walbro MDC 15

[elittle]

So I'm pressure testing a walbro mdc 15. On the top of the carb there is a black round clip holding in a screen near the fuel inlet. If i put the carb in a jar of fuel and pump it up all the air comes out through that screen.

I've tried 2 different diaphragms, 3 needles, adjusted the height of the lever 5 or 6 times.

Any idea what is leaking? I've watched several YouTube videos and this and the zama that was used on the mac 130 are identical looking and they all appear to pressure test by just hooking up to the fuel inlet.

Thanks for any info. I've spent hours trying to get this thing working lol.bubbles are coming out that big screen.

 

[Old2stroke]

have you got the gasket on the right side of the diaphragm? In the fuel pump it goes between the cover and the diaphragm, on the dry side of the diaphragm.

 

[elittle]

Yes, I've got it built like the instructions show. I have a second same model carb, built it up, same result. It's driving me nuts.

 

[Chevboy0167]

Here is the MDC 16....... look similar?

 

[Chevboy0167]

 

[Old2stroke]

Yes, I've got it built like the instructions show. I have a second same model carb, built it up, same result. It's driving me nuts.

That screen just covers a vent passage that goes down to the dry side of the metering diaphragm to keep that side of the diaphragm at atmosphere pressure. Check the pathway through the gaskets and diaphragm and mid section of the carb, somewhere there must be a fault (wrong gasket/diaphragm or located wrong) that is letting fuel into the air passage.

 

[elittle]

Here is the MDC 16....... look similar?

View attachment 1242921

It looks identical. The mdc 11, 15, 16 all seem identical, not sure if they really are. But that sure looks like it.

 

[elittle]

That screen just covers a vent passage that goes down to the dry side of the metering diaphragm to keep that side of the diaphragm at atmosphere pressure. Check the pathway through the gaskets and diaphragm and mid section of the carb, somewhere there must be a fault (wrong gasket/diaphragm or located wrong) that is letting fuel into the air passage.

Thanks! Appreciate the help. I will try to figure it out.

 

[elittle]

That screen just covers a vent passage that goes down to the dry side of the metering diaphragm to keep that side of the diaphragm at atmosphere pressure. Check the pathway through the gaskets and diaphragm and mid section of the carb, somewhere there must be a fault (wrong gasket/diaphragm or located wrong) that is letting fuel into the air passage.

I did put in new welsh plugs. If they aren't sealed correctly would that cause that kind of an air leak?

 

[elittle]

So I saw a thread somewhere that said to soak the gaskets in 2 cycle oil. I did that, made sure everything was lined up correctly and it's holding 7psi like crazy. Thanks to everyone that replied, I appreciate the help!

 

[elittle]

What's funny though it's i tried it on a carb with no welch plugs put in. So now I need to get it to work on the good carb lol.

I think i took the carb apart so many times the gaskets got smashed and weren't sealing proper. I also made sure to put fuel on the check valve and needle and it worked.