Repairing Walbro Check Valves

[Randall Ward]

I have a Walbro 21-85 off 10-10 McCulloch. How do you remove the check valve?

 

[Old2stroke]

I too have found the carb diaphragm to be too thin so I bonded two of them together with crazy glue to get the right thickness. They seem to stay together so far.

 

[Ax-man]

I concur , interesting thread. It wasn't until threads like this popped up that you could take those main nozzle check valves out of the carb let alone repair them . I have tools like that leather punch also but never realized you could repair a small engine carb with it along with punching holes for homemade gaskets.

 

[Jasonrkba]

I may have to switch to decaf before trying this.

 

[Ax-man]

I hear ya, teeny tiny detail work to fix a check valve. Need a steady hand and sharp eyes to do this.

I need some saws to work on to try out some of this new info that has been surfacing lately here at AS. I have had some time on my hands lately so I have made a few customized tools to work on them but alas no saws to try them out on.

 

[Old2stroke]

If you can't find the exact right punch, you could try this:
https://www.arboristsite.com/community/threads/make-your-own-punches.327240/

 

[Jasonrkba]

Gonna revive this one. I suspect a bad check valve on a walbro HDB thats in my mac 610. Did anyone find a suitable material to use? Do you think thin mylar would work? This is the first time I am going to try pulling one out. Usually I just replace the screen.

 

[Chris-PA]

Stopped in and noticed this thread - I found an old note, and the rubber I used was 0.014” thick. It came from the diaphragm of an old GM charcoal canister purge valve!

I know that’s obscure, but I have a bin full of old vacuum emissions devices and such from back in the day when such things still existed. I thought at least it might help to know what to shoot for.

 

[Jasonrkba]

I made one from plastic. Im not sure if it works yet because the saw is broke all the way down. I used the blister package from a spark plug. I tested the plastic by soaking it in gas for a couple days. It did not warp or change so hopefully it works because it fit perfect. I have to order new seals and my saw budget is blown for a few weeks.

 

[Jasonrkba]

I'm still kicking around ideas for this and think I might have found something that may work. Polyolefin seems to be extremely resistant to gas. So I searched for different materials made from this and heat shrink for wiring came up. It seems to be about the same thickness and is flexible. The larger diameter may stay flat enough to use. I haven't tried my other fix yet which is basically pvc.

 

[philbbb]

I have accumulated several Walbro WT's, and one WT Chinese clone, that have bad check valves. Usually they pull air through the main fuel port when you pump the purge valve, so you cannot get the air out. This leads to hard starting, and if it's bad enough they may not run. It's a common failure mode and has been quite frustrating.

Walbro has used various fuel outlets/check valve arrangements - some of them have a brass fuel port pressed into the venturi, and some have just a hole drilled at the edge. The ones with the brass insert seemed complex and I had not figured out how they worked, but I needed to fix one so I looked at it more closely. I should have known it would be stone simple!

The ones with the brass insert have 4 thin tabs around the outlet that curl back inward, trapping a small flat disc underneath to form a one-way valve.

View attachment 390162
Some of these are black rubber discs, and with the throttle shaft removed you can reach in with an appropriate tweezers and pull it out. The rubber is 0.010" to 0.012" thick, and quite flexible. The carb I was trying to fix was actually a Chinese "HTIC" clone of a WT, and I hoped to use the disk from a scrap Walbro, but it turn out they used a smaller disk than the Walbro. The Walbro disk is about 3.5mm, and the clone is 3mm. So that meant I needed to make one!

I searched around in my bin of old carb and vacuum emissions parts, and found some appropriate rubber. It was actually a charcoal canister purge valve diaphragm from an old Jeep (probably a GM part). Then I grabbed a leather punch and did a little clean up on the punches. In this shot the original factory disks are on the left, and the ones I made are on the right:

View attachment 390163

The small disk on the lower left leaks, but I'm not entirely sure why - it is mildly potato-chipped so I guess that must be it. Once I made the disk I was able to place it over the brass fuel outlet and tuck it under the fingers. The part worked - it is not 100% air tight, probably because the material I used had a little curl to it, but it's as good as some I've had from new. It held 10" of vacuum, but it still leaks a tiny bit of air. I am curious to see if it holds up to the E10 fuel I use, and will be looking for an other source of material.

In the end the original carb is back in my Earthquake and running well, so it was a successful repair.

Here are the tools and materials:

View attachment 390164

View attachment 390166
I looked at a couple of other carbs, including the WTEA-1 from my Dad's 455R, and it had a clear plastic disk that was way too hard to remove intact. I used a hot wire to burn a hole in it and then was able to remove it. I put a rubber disk in but I could see I marked up the brass surface getting the old one out - it did not seal very well. I don't know if the original disk started out that hard or not - it's hard to see how it could seal if it was. I suspect it deteriorated due to my Dad's use of inappropriate fuel containers.

Thanks for the post...about to attempt this. I may actually use my 3d printer with tpu to make the disk.

Im left with a few questions though. I received this carb after the disks were blown out.

1) You mention the disk should be 3.5mm diameter, but the picture shows two disks. They appear to be different sizes.

2) Can anyone explain to me how the two disks are arranged (Im guessing large disk on top to retain smaller.

3)And what the sizes of the individual disks are?

Thank you!

 

[sean donato]

His disks are from 2 different carbs, 3.5mm and 3mm. You need to make the disk to fit the specific carb you're using. Tpu should be a good choice, has good chemical resistance properties. Getting thay first layer super smooth and flat would be the challenge.

 

[philbbb]

His disks are from 2 different carbs, 3.5mm and 3mm. You need to make the disk to fit the specific carb you're using. Tpu should be a good choice, has good chemical resistance properties. Getting thay first layer super smooth and flat would be the challenge.

Ahhh, okay....in the first image he shows two sets of disks. That made me think there were multiple peices in the valve, and thats kind of how it looks on the parts diagram as well. Thanks for the quick reply!

 

[sean donato]

Ahhh, okay....in the first image he shows two sets of disks. That made me think there were multiple peices in the valve, and thats kind of how it looks on the parts diagram as well. Thanks for the quick reply!

Two carbs, old and new disks for each if I recall correctly.

 

[philbbb]

I was able to 3d print a diaphragm that worked successfully. Maybe not perfect, but good enough and could probably be improved with some trial and error.

Mine had to be smaller. I think 2.6mm Di x 0.2 mm, but then maybe that's just the loose accuracy of the printer. Done in TPU on smooth PEI, with the smooth bottom sitting against the valve matting surface.

I realized the tangs holding the diaphragm need to be tuned a bit to let the diaphragm float up but not enough to block the large exit port.

 

[Vintage Engine Repairs]

Just as a reference for anyone in the future, Ideally that valve should be air tight when wet. However there is an allowance, so if you replace that valve and it leaks a bit, so long as it’s slower than 4-5 seconds per 7psi you’re fine