Salvaging the Walbro carbs

[400brian]

The WRA-31 Walbro carb was first used on the 74 JDX8, eventually being used across the line on the mid-mounts. It cured the issues the 73 JDX8s had with an over rich mid-range. I have ran one on a 340/5, 440/21, and a 440/22 with good results.

I have picked up several in the past few years with the idea of having a spare, and I don't have one yet. I like to see really greasy dirty carbs as I have had the best results with them vs. the clean dry ones with the powdery corrosion on them.
The complete carb pictured here is what a brand new one looked like. The one I have opened up is what I have too often been seeing. I am posting this to relate how to try to salvage them.

The biggest issue I have found is when I remove the 4 screws that hold the plates to the main body, revealing the more or less rectangular metering plate that is held to the main body by 3 countersunk screws.
What happens is that if you twist off any one of these screws, you have a junk carb ( at least as far as I am concerned ). I have a growing collection sitting on my bench, and it is rubbing me the wrong way.

The carb pictured looked like a good candidate. It was greasy and black, and nothing was stuck. But, when I dropped the plates off, I was looking at an orange with rust metering plate, and you can see what the rest of the chamber looks like.
I was PO'ed, but I decided to take a shot. I couldn't get the screw that holds the metering lever out, so I warmed it up with the propane torch, knowing I would sacrifice the spring under it in the process. After applying heat to the screw head and from underneath though the throat, I cracked it loose. The spring had lost it's sprung, so it was tossed.

So now I am up to the metering plate screws, this is for all the marbles. These screws are smaller and the counter sunk heads add to the area to corrode. I heated the plate , the idea was to cook the gasket and take some of the tension off the heads. Then I began heating the underside of the area. I had a small screwdriver that fit the slots well, and carefully tried them. Being as I have twisted them off before, I had a little idea of how much force I could use ( not much ).

I figured patience was a virtue here, so I heated them up, let them cool, tapped on the heads with a small punch, heated everything up again. I did this several times, trying not to force things, finally one came, more heat and another screwed out, and finally the last one was out!
This is the first time I have successfully removed metering plate screws that were stuck! If the carb is clean and shiny inside, these typically are no big deal.

So, the carb is soaking in the solvent. When it comes out, the whole thing will get scrubbed with a brass bristle brush ( like a tooth brush ) to try and get the corrosion off. Then I will have to decide if it is worth a carb kit.

[Matt]

Great post Brian. I'm curious how you do with getting that crap out of those passages there.

[400brian]

After a week soaking in the pail of Chemdip, and some scrubbing, it looks like I may be able to salvage this one.

[AirborneX4Special]

Wow
Can think of some other places and things that might need a week or more of soaking in Chemdip to clean out the filth.

[400brian]

The main issues I have found with these carbs is that the diaphragms get stiff and crunchy. The fuel pump diaphragm flapper valves curl up over time, and I had a broken aluminum leaf valve in my 74 X8, and look at the crud I dumped out of the most recent rebuild.

[400brian]

So I scrubbed the plates with a brass bristle brush about the size of a tooth brush, and got everything much better. I noticed there was a divot in the base surface right beside the fuel return port. I hadn't noticed before, and this was probably the single worst place for a sealing issue ( If you refer to the photo above, look just the the right of the needle seat at the edge of the base ). The way things stood, it appeared gas was going to leak at that spot, there was no way the gasket was going to seal. So I applied a dab of JB Weld and sanded it smooth.

I paid special attention to the area the idle mixture needle screws into, got that as clean as I could. I replaced the packing on the idle mixture needle, that is the larger of the 2 O-rings in the kit, the other is for the high speed needle, and they need to be replaced as these were rock hard.

The choke assembly had been robbed off this carb, so I had to take one off a donor carb. A bit of heat was applied to the screw as it is put in with thread locker. After the butterfly is pulled out of the shaft you can slide the shaft out, taking care so as not to lose the spring and ball that is under the shaft.

After cleaning up the shaft and butterfly, I slid the shaft back in. I had never messed with a choke before, I typically leave them alone. I was worried about losing the ball on installation, but I got everything back in without much issue. Red locktite was used on the screw, you don't want that backing out.

The carb is all back together. It will be on-deck in case I have need for a quick replacement. I have not tried it out, so I have no way of knowing if it will work or not.

[jep_800]

Most guys aren’t too keen on the Walbro’s, preferring the Mikuni’s instead. But there’s a handful of us who use them regularly and like them. They’re quite similar to Tillotson carbs that were used on early Cat’s and others…. (I think I’ve seen Walbro on Cat too). My opinion is the manufacturers would not have used them if they found them to be unsatisfactory during production. The key, as Brian states is having clean passages, good flat surfaces that the gaskets will seal, and finding the correct settings…. One of the items that did change a bit from original is the replacement gasket & diaphragm kits are slightly different which guys discovered that the metering lever arm needed to be adjusted lower (nearly flush with the carb body). That prevents spill back of gas coming back through the throat of the carb.

I have two on CCW KEC 440/22 engines. When clean, and set correctly, they run fantastic! Yeah, there isn’t as much fine tuning that you could get out of a Mikuni, but for great idle and trail riding, I find that they are a great carb.

[jep_800]

The WRA-31 is getting harder to find or I should say harder to find complete and which doesn't get damaged upon tear down... I was lucky that David Clark had one off his 800 which he donated to me to strip down and build up again. This carb had a few issues, but the metering plate and machine screws came out without breaking, so that's a huge battle won. There's a couple missing parts which I've sourced so hope to have this back together and on hand as my spare. Another one saved from the scrap pile!

[jep_800]

Carb is finished and waiting to be used. I'm thinking of actually putting it on my 800 to see if it's as good or better than the one I have on it. That's the problem with these rebuilt carbs is you don't know what you got till you run it, so might be worth the effort to see it in action. We'll see.

[400brian]

Here is an update on the carb I rebuilt at the beginning of this thread.

The first time I tried this carb on an X8, I quickly found I had fuel spraying out of one of the upper plates that has a vent opening out the side near the impulse fitting. So it went on the shelf for a while to think about what it had done.

I recently pulled it apart and looked at the plate in question. I didn't really see anything wrong with it, but there had to be a reason for why it was leaking, so I pulled out the magnifying glass and took a closer look. I quickly identified a couple of places where the sealing rib that is molded into the plate was deteriorated. There seemed to be a break in the rib near the dogleg at the top of the plate in the photo, and another between the two halves. I believe this is referred to as the fuel pump plate, and being as the one side is vented, there shouldn't be any fuel on that side.

I have a box of junk carbs on the shelf, so I picked out a couple of the same plates and cleaned them up and then took a close look at them. Pictured is the one I decided to install.

I recently put the carb on a X8 and tried it again. The fuel spraying out the side seems to be resolved. As I write this I am still in the process of getting the metering arm set correctly, I'll post the results when I know more.

There is a lot of talk around the snowmobile community that the square bottom Walbros are junk. I tend to disagree, but I will acknowledge that 50 year old carbs in many cases have degraded. I suspect this is why some of these carbs just won't work correctly. Recently I am hearing the same thing about 50 year old Mikunis as well, so it isn't just the Walbros. Everything thing we own is busily trying to oxidize it's way back to base components, ie. ore!

So besides thoroughly cleaning the carb, and scrubbing off any corrosion, I suggest taking a really close look at those plates, and make sure that there are no breaks in the ribs that may be allowing leaks inside the carb. I assume you will notice any leaks to the outside. A properly functioning Walbro is a beautiful thing. They allow for easy fuel mixture adjustment to compensate for temperature. Keeping one on your mid-mount allows you to keep the original air box in place. Swapping it out for a Mikuni is not a cure all, just a different set of problems.

[cordes42]

Im curious where did you find a carb kit for the walbro? I only ask cause i have seen on here that some aftermarket may cause issues.
thanks

[400brian]

Vertex is what seems to be available right now, New Breed should have them. I have also used SPI with good result. Genuine Walbro kits, full or just gaskets and diaphragm, haven't been available for years now.

[cordes42]

Okay thank you ill order one from there.

[cordes42]

I got mine rebuilt and it still puked fuel out the throat when you would idle down. So I adjusted the lever inside, i went to flush or a little less it wouldn't start. Now theres barely daylight under the arm and it starts and runs good for what I think. But if you stop and idle for a minute it won't take back off without pumping the throttle. Do I still need to mess with the lever or something else?

[400brian]

Sounds like you are close. When it is up to operating temp, is the idle stable, spool down and die, or does the rpm hunt up and down?

How many turns out is the idle mix needle?