Discussion Walbro

[antique]

Walbro web site, Tech Tips, metering lever setting, read the whole thing...I'm a NOOB for explaining it this way...
You can believe Walbro's Luiis Salas or Jodi, Pat, and a few others on FG. Your choice...
Good info on high and low needles there too...

[antique]

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[Jedijody]

Not sure what you're talking about, I nor Pat has ever argued with what the tech tip states about the metering diaphragm. In the referenced thread, someone else jokingly called you a noob, not me or Pat, you seem to have taken it seriously.

And the pinch test is worthless on a GS gasser unless you're running a fuel injected racer with nothing but a venturi, so there.

[Rickster]

If the cowling is off I still use a pinch test to verify how fat a idle setting is.. What I am looking for is to see how much RPM is gained during fuel starve.. It does take a little while to get the results though since you are waiting for it to dry up the fuel side of the carb...

Rick

[antique]

The thread was about atmospheric pressure pushing the diaphragm down...No one but myself said it did...So does Walbro...
And if the idle is rich and the fuel is cut off, the engine WILL speed up before it dies...If it's lean it will just die..
So there

[Rickster]

I too agree the Diaphragm is a pressure sensing/acting item.. That makes it "Self" tuning to many changes in atmospheric conditions which allows the gas engines to pretty much be set and forget for year round flying, same reason chainsaws are sold everywhere in the world and seem to "Work" without too much hassle...

Rick

[Kcorb]

	Quote: Originally Posted by Rickster
	I too agree the Diaphragm is a pressure sensing/acting item.. That makes it "Self" tuning to many changes in atmospheric conditions which allows the gas engines to pretty much be set and forget for year round flying, same reason chainsaws are sold everywhere in the world and seem to "Work" without too much hassle... Rick

I respectfully say if you read " THE WALBRO TECH. MANUAL" you would not post this reasoning.

[Rickster]

	Quote: Originally Posted by Kcorb
	I respectfully say if you read " THE WALBRO TECH. MANUAL" you would not post this reasoning.

If the diaphagm is not affected by atmospheric conditions then explain why changes in cowl pressures directly affect the mixture. Seems to me the atmosphere side of the diaphagm is directly affected by the increase/decrease in surrounding pressure thus changing the relationship between the low pressure inside the venturi where the fuel is admitted and the outside (Atmosphere) pressure conditions. This is also changed by the barometric pressure acted upon the diphragm resulting in some tuning effect for corrections due to weather changes..

Keep in mind I am referring to the large pressure diaphragm and not the pump side diaphragm.

Rick

[robbinsp]

n00bs

[RTK]

Too bad they don't include accelerator pumps on more models of walbro carbs

[Super08]

You have it all wrong Rickster. It is not there to allow for corrections. It works in relationship with the vacuum created within the venturi to allow the needle to be lifted off of the seat. Changes in atmospheric pressure act upon this diaphrame to our disadvantage as stated when you get a pressure or a vacuum in the cowl and changes the mixture on us which then requires us to change the needle settings to correct the mixture or better yet fix the airflow problems with in the cowl. When it gets cold in the winter you need to richen the mixture for the colder denser air or if you go from a place near sea level and go to a meet say in Denver will require you to lean your needle settings. The diaphrame does not do this for you. The diaphrame just acts as a barrier so that when the carb starts to develop a vacuum it allows the ambient air pressure to push against the diaphrame which opens the needle off of the seat to allow more fuel into the carb. If the engine is not running the pressure is equal on both sides of the diaphrame and the needle will be closed. When you change air pressure it changes inside and outside the carb at the same rate unless the engine is running. It will not compensate for us. As you go up in altitude the air pressure acting on the diaphrame will be less as you are thinking, but is will also be less on the inside of the carb so it balances out and there is no compensation for altitude. It must be done with the needle settings.

[Low_Cal]

	Quote: Originally Posted by RTK
	Too bad they don't include accelerator pumps on more models of walbro carbs

I agree, then we could have a leaner setting and still get the engine to accelerate without dying. I tried a Syssa engine with accelerator pump carb, but unfortunately I didn't realize the advantage, perhaps due to other issues.

As for the diaphram, yeah all that does is emulate a float bowl in a standard carb, one that works in all positions. Unfortunatly it doesn't compensate for altitude, weather, etc. Proabably need electronic fuel injection and a bunch of sensors to do that.

[antique]

	Quote: Originally Posted by robbinsp
	n00bs

Welcome to the club, guys....
I'm NOOB #1, the rest of you can sort it out....

[jm_mac]

They should have these on DA engines...........

[antique]

I thought DAs were perfect....Most accelerator pump carbs are only on carbs too small for anything over 50cc..