Walbro Spiral Diaphragm K3-WYTA

A lot has changed in our industry with emission regulations, and especially the addition of ethanol in our fuel. Ethanol continues to be a problem for diaphragm carburetors, and Walbro is pleased to introduce a new pad and metering diaphragm, which is the first major change in over 60 years.

This new assembly is impervious to the effects of ethanol and does not deteriorate with age. This is a new spiral metering diaphragm assembly.

Mike Patella was a Walbro senior principal engineer. He was the lead engineer on the project that will revolutionize the small engine industry.

Mike, what's this all about?

“Well Louie, to fully understand the changes we made, let's take a look at what used to be done. It's rubber coated over a fabric. It has a rib around the washer that we call convolution, and has a rivet in the center to hold the washer on. We've had challenges over the years getting a good seal around that rivet to prevent a leak path. The convolution can be a challenge to produce consistently, and of course the rubber deteriorates with age, especially when ethanol or acid is introduced from the fuels.

Now let's look at the new spiral diaphragm. Our new spiral diaphragm has two key components: the membrane and the spiral.

Let's talk about the membrane first. It has a high-grade Teflon film in the center and a Mylar carrier for handling. Also, you can see it has no hole and no convolution, solving those problems we've had for years.

We've set up this display to show you the difference between a conventional diaphragm and our new spiral diaphragm. This stainless steel spiral is a key component. It provides structure and support for the membrane. When the membrane is moved by engine vacuum, the spiral transmits this movement to open the inlet valve. Of course, we use stainless steel so that it will be impervious to ethanol and harsh fuels.”

“So what I'm hearing is this could be the last metering diaphragm assembly I should ever have to put in my carburetor?”

“Yes, Louie, if you install it correctly. These parts are very durable in the carburetor, but somewhat fragile to handle, especially the membrane. You have to be careful not to bend or crease it, as you will damage the part. The spiral is more forgiving, but you still need to be careful handling it.

Let's take the old assembly out of the carburetor and install a new spiral diaphragm.

So first, remove the metering cover, the old diaphragm and gasket, and we have to replace the metering lever.

And as always, this is a little bit of a tricky process. Remove the pin from the old lever. Install the new metering lever.

As you can see, there's a little spoon shape on the new metering lever. This is our new metering lever gauge that's included in the spiral diaphragm kit. The adjustment point for the spiral is on the bottom — it's actually an indentation. This metering lever will extend above the gasket surface slightly. You need to check that adjustment.

Anyone who has ever rebuilt one of these diaphragm carburetors knows they can get a little tricky handling these small parts. We've come up with an ingenious way to make installing this kit easier. So we've contained all the parts in this assembly. Install it on the carburetor on the two pins, hold it with one hand, put the metering cover on over top of it to hold it down, install the four screws, and start them just one turn each.

Then simply remove the clip off the end and pull the sleeve out, and then torque the screws down as normal.”

“Mike, you made the process so much easier. That was awesome.”

And right now, over 500 Walbro diaphragm carburetors can be retrofitted to use the spiral diaphragm kit, and the list is growing. Go to our website and click on parts and service for the complete list of carburetors.

Thanks for watching, and remember to watch for more service videos in the future. And remember to use our website as a very important tool for servicing your Walbro carburetors and products.

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- Consistent performance whether it becomes wet or dry and most importanty does not stiffen or deteriorate with age. Diaphragm's functionality is not affected by temperature extremes.

- Features an inovative design highlighting robust materials like an ethanol proof membrane and a stainless steel spiral support

- Diaphragms provide greater reliability as variations in the molding and rubber application process have been eliminated. Rivet-free design eliminates possibility of leakage.

- Consistent wet-or-dry performance reduces variations in emissions from the factory to the field