Husqvarna 555 Carb test, what is this hole?

[Broke Again]

Trying to pressure test this Zama el49. I'm getting bubbles out of this hole on the back face. It goes through a weird hole in the intake underneath the main boot.

What is it for? Is there supposed to be air coming out when pressure testing? I cant find any explanation for it.

 

[J D]

That would be the impulse to drive the pumping diaphragm (which probably has a crack in it)

 

[Broke Again]

Thank you. I just put a new diaphragm and gasket, as well as new reed valves and a gasket in it. The reed valves are on the bottom and the diaphragm is on top. Does the impulse travel through the body to the top of carb?

 

[Old2stroke]

Thank you. I just put a new diaphragm and gasket, as well as new reed valves and a gasket in it. The reed valves are on the bottom and the diaphragm is on top. Does the impulse travel through the body to the top of carb?

What exactly are you calling "reed valves"?

 

[Broke Again]

What exactly are you calling "reed valves"?

These things. Sorry I've heard them called reeds before and my mind immediately went to snowmobiles



These are the old ones in the order the Husqvarna states. The black one on the bottom against the carb, the clear one in the middle, and the gasket on top.

Last night I pulled it apart again after reading about a few people having trouble getting new gaskets to seal, one solution was dipping them in mixed fuel. I figured I didn't have much to lose since buying a new carb is almost more cost effective. I tried it and it worked, it held 20kpa and didn't move at all for thirty minutes and I have no leaks through the impulse. I'm guessing it was just leaking through one of those reservoirs into the impulse channel.

I hope I didn't hurt the gaskets by doing that but for now im going to say its fixed. Ive also heard people saying new carbs sometimes won't hold pressure, but after they run for a few minutes they hold fine. I'm thinking maybe the same thing is being accomplished once fuel is in the carb? I will see what happens and test it after a few tanks.

 

[J D]

If you assemble a carb dry & it doesn't hold pressure first thing to try is a bit of mix through it. Can usually open the metering valve by pressing the dimple on top of the metering diaphragm through the vent in the cover plate to allow fuel to pass through. Carb should hold about 70kpa indefinitely & will usually "pop off" around 100kpa

 

[Old2stroke]

View attachment 1045153

These things. Sorry I've heard them called reeds before and my mind immediately went to snowmobiles

View attachment 1045154

These are the old ones in the order the Husqvarna states. The black one on the bottom against the carb, the clear one in the middle, and the gasket on top.

Last night I pulled it apart again after reading about a few people having trouble getting new gaskets to seal, one solution was dipping them in mixed fuel. I figured I didn't have much to lose since buying a new carb is almost more cost effective. I tried it and it worked, it held 20kpa and didn't move at all for thirty minutes and I have no leaks through the impulse. I'm guessing it was just leaking through one of those reservoirs into the impulse channel.

I hope I didn't hurt the gaskets by doing that but for now im going to say its fixed. Ive also heard people saying new carbs sometimes won't hold pressure, but after they run for a few minutes they hold fine. I'm thinking maybe the same thing is being accomplished once fuel is in the carb? I will see what happens and test it after a few tanks.

Yep, reed valves are a totally different animal and not part of a carb, they are a type of flapper valve that provide one-way valve function when the carb in mounted directly to the crankcase. Those two little flaps in the pump diaphragm are check valves that keep the fuel moving in one direction, assembling them with a bit of light oil or some premix helps with the initial sealing. If you have a choice of pump diaphragms in a repair kit, the best one is the tan (teflon) one, best compromise for fuel delivery and chemical resistance to damage.

 

[pioneerguy600]

Thank you. I just put a new diaphragm and gasket, as well as new reed valves and a gasket in it. The reed valves are on the bottom and the diaphragm is on top. Does the impulse travel through the body to the top of carb?

The impulse moves those flapper valves but does not affect the metering diaphragm.There really is no top or bottom to a chainsaw carb as they can be mounted in any position. That is why on chainsaw carbs there is a metering side and pump side to make it clear which side is being worked on or trouble shooting.