Chris-PA
Where the Wild Things Are
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.
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:
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:
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.
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.
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:
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:
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.
