Salvaging the Walbro carbs

[cordes42]

I ran it Saturday for awhile. And somehow the bog at idle is gone but it's hard starting after sitting over night in a heated shop. The idle screw is at 1 and a quarter turn.

[400brian]

Do you have the screened pickup fitting in the tank with a check ball in it? ( they came with and without ). This prevents the fuel from running back to the tank. I find they work best if they hang straight down.

This sounds dumb, but what is your starting procedure? The Mikuni guys try to start these without touching the throttle, which doesn't work. For first start of the day; Pull choke, open throttle half way, crank till it fires...sometimes you can get the choke pushed off and keep it running.

[cordes42]

Yup that works so much better to start now. Still have fuel residue at the intake of carb. I have adjusted the lever to .015 so I'm going to keep going down. Still boggy at the low end again.

[Cdnturboz]

Brian Quick question - I rebuilt a WDA-32 to convert my 400 over from a bendix, it’s idling ok and has a slight bog when taking off, but the big issue is when I turn off the sled I get a big burst of fuel shooting back out the carb/makes a mess.

Would this be similar to the issues a above with the float arm needing adjustment? (It’s an aftermarket rebuild kit)

[400brian]

I have to say I have never seen backflow of fuel on shut down. If you run with the engine plastic and the airbox removed it is normal to see some spit back on the front of the seat after a test rip.

On the slight bog, Sometimes adjusting the idle mixture screw up or down a little can resolve the acceleration bog.

Taking the two together, my first thought is that the metering lever may be slightly high,

The only Walbro kits that seem to be available right now are the Vertex, I believe they bought out Windrosa. Over the years I have had success with SPI and Windrosa kits. But I gotta tell you, I have struggled with the Vertex. I have found it really difficult to get the metering lever correct.
For years I was setting the arm just slightly above flush with the carb body, and they worked. Now if I set them there they are starving for fuel. I never measured the things, I just set them by eye and they ran. I am going to have to start measuring them I guess, just so I can tell guys where the sweet spot is now. At the moment I'm not sure there even is one.

I was trying out a WRA-31 I had put together as a spare this winter on my 74 X8 with the 440/22. First it was way too rich, I set the arm down and it then idled great, but topped out at 40 mph. I set the arm up a bit more and it hauled ass, but now it acts like it is way too rich at idle, almost as if the arm isn't allowing the needle to close completely. The carb doesn't overflow or anything that obvious, but it doesn't want to idle well and there is a bit of a bog until it clears out and hauls. Also adjusting the idle mixture screw seems to have little to no effect I can close it tight and it keeps idling.
We had little to no snow most of the winter, so I had limited time and conditions to test in.

I have a WDA-32 on a 340/5 engine, and it has performed great, so I do not believe there is any issue with that carb on a 340.

[Cdnturboz]

I took it all apart and adjusted the arm just just above the plate - fired it back up and no more fuel blow back but after a few secs it starts starving for fuel (needed to give it some primer to keep it running. It’s spitting zero fuel (light amount on the seat kind) I think I’ll tear it apart and adjust it slightly higher to give it more fuel.

[400brian]

Lately I have been starting with the arm above the base about the thickness of the arm, and the tweak it from there.

[Cdnturboz]

I went higher than you mentioned above (read your reply after the fact) - idles and starts great (first time I’ve had it idle properly in the 6 years I’ve owned it) no fuel blowing back - but I have a bad bog at full throttle - almost floods it/stalls. Once it hits full throttle it’s fine, it’s if I’m at lower speed and give it full throttle it seems to flood.

I have to almost stop and give it some throttle to clear out then it runs fine. It’s for sure rich in the top end as there is a bit of excess fuel/oil leaking out of the exhaust at the jug after a higher rpm pull.

I have the high speed jet 7/8 out as per the manual - leaning out the high speed needle about a 1/4 turn in helped but not great. It’s super warm out today, +1C (34F) so I might try later this week when it’s colder out too.

[400brian]

I have been having the same experiences trying to find the sweet spot where it works on both ends. They didn't use to be this finicky to set. I am still hoping to find the sweet spot. I have been messing with 2 different WRA-31s, and while I certainly have made some progress, I'm not there yet. That is why I guess I am going to have to start measuring my setting, so I can tell exactly where I am, and document the effect.

[Cdnturboz]

What were the rebuild kits you weren’t having problems with? I might try and find one of those

[400brian]

Windrosa or SPI

[jep_800]

I've experienced most of what you and Brian have been discussing on both my 800 and JDX8... I've currently found that if I have the metering arm slightly above the body, it gets all the fuel it needs on both idle and between 1/2 - WOT. The slight bog here and there, I've been able to adjust away by playing with my low speed and high speed needles. Currently my 800 is damn near perfect. Idles great, throttle response is great, good top end, pulls hard, and has that wonderful throaty growl you get through the tuned pipe when you come to a stop... and it goes right back to perfect idle. I hate to even breath on it, so I don't mess it up.

The JDX8 is close, but I don't seem to have the top end that the 800 currently has.

I found that Winderosa kits were pretty good... I agree with Brian that Vertex is not as accurate. I've looked hard to find actual Winderosa and not a Vertex that advertised as that, but they're really hard to find. I did find an SPI, and I cannibalized that kit and a Vertex kit to rebuild a spare I have on the shelf. I had to inspect every gasket and diaphragm, and even did some trimming hoping to make sure everything is lined up as it should. Haven't tested that one yet.

Jason

[400brian]

I rebuilt the engine in my 74 X8 back in 2021. I rebuilt the Walbro WRA-31 at the same time. I had put 2000 + miles on the sled after having gotten it running in 2007. Excessive end play at the crankshaft was the reason it was rebuilt.
Since the rebuild, I have not had a good time with the sled. Despite having good success with Walbros up to that point, I just couldn't seem to get the rebuilt carb dialed in. The problem ranged from over fueling to running short of fuel at the top end.
The most recent apparent issue seemed to be over fueling. If you refer to the first photo, you can see the black goo has been spraying out of the exhaust. In my experience this indicates gross over fueling, or an engine running on one cylinder. The spark looked good, so more tinkering with the carb seemed in order.

Last night I pulled the plate stack off and adjusted the metering lever. Normally I just eyeball it, and they work. As noted though, recently that has not been working. I laid a piece of .030 thick steel across the gasket surface and wrote down where I estimated I had it set. I then pulled a spare WRA-31 I had taken off because of the same issue, adjusted the metering lever, noted and recorded that position, and put the carbs in a box for testing today.
For whatever reason, I felt the most confident about the sled's OEM carb. I bolted it on, fired up the sled, and it ran terrible. Smoking profusely, no throttle response, and would not idle. I didn't waste much time with it before deciding to try the second carb.

When I originally acquired this carb, it was a mess. Corroded, rusty, and oxidized. Guys told me not to bother with it. However, the three metering plate screws were successfully removed with some heat, so I went through it . I think I tossed one plate as too badly corroded, and the main body got a dab of JB weld to fix a sealing surface. I had tried running it a couple times over the past three years, but it didn't work any better.
So today I bolt it on and crank her over. She barked right off, and idled nicely! The throttle response was excellent, and the smoke was at normal levels. I decided a test rip was in order. We got a dusting of snow this afternoon, so the lawn looked like the test track. I would like to test it on a longer run, but there simply wasn't any place to do that.

I pulled it out of the garage and fired it up. After getting it lined up on a short straight, I punched it. Holy cow! That sucker hooked up, pulled the skis off the ground, and hauled ass! I couldn't believe it, the sled hasn't ran like this for ten years. So after ripping around the lawn for a bit to verify this wasn't a fluke, I put it back in the garage to get the goo cleaned off and everything put back together. Dang it, it is going to have to go in the trailer with the rest. Heading for the Ride with the Champs next week.

[400brian]

Another thing I have just learned is a tool to clean the Walbro inlet seat. It is called a tortilon, it is a tool made of wound paper, and is used to blend charcoal and pencil art work. The seat is not replaceable in the Walbros, so the best you can do is polish them. Some have tried Q-tips, but it has been pointed out that a 3/16" dia Tortilon can be used with a little polishing compound to shine them up. I found these on Amazon.

The following was posted on the Walbo Face Book page:

We've been having some good discussions lately regarding the WD, WR, WDA series of a Walbro Snowmobile Carburetors. Here is another important tip to consider when you are rebuilding one.
Unlike the Tillotson models, the inlet seat is secured into the throttle body and it is not replaceable. These are made of brass and like most non-ferous materials, it is subject to corrosion. A corroded or dirty inlet seat can cause inlet needle sealing issues that result in hard starting due to loss of prime and/or excessive flooding.
The fix in this case is to use something called a tortilon. These are available at any artist supply store like Michael's or Hobby Lobby. Office Max or Office Depot may also carry them. Of couse, there are plenty of online sources for these too. They are made from tightly rolled paper and come in various sizes.
To resolve a corroded or dirty inlet seat, use a 3/16" size tortilon with a small amount of polishing compound or cleaner wax to the tip and the sides. Toothpaste also works since it's a mild abrasive. It'll slide in and since it's made from paper, it'll conform to the taper at the orifice of the seat. Twist it around by hand for a bit and the tortilon witll blacken as it cleans the dirt and corrosion from the brass. Use a Q-tip to clean out the seat occasionaly and to check your progress. Once the Q-tip comes out clean, you've gotten it as clean and corrosion free as you will likely manage. Use some solvent to thoroughly clean any residual compound from the seat, install a new inlet needle (Walbro PN 82-30-7) and you have a fully refurbished inlet needle and seat.

[400brian]

Another good post from FB:

The documentation on inlet lever height is somewhat fuzzy. Both of those types of metrering diaphragms are original Walbro equipment. I have more commonly seen the "buttonless" style on the right used with carburetors meant for a multiple carburetor arrangements like the WD2-1, WRD -1 and the WD1-1. The remainder of unmolested carburetors that I have run acrosss had the button type on the left.
Service instruction documents illustrate the inlet lever adjustment both ways: 0.005" - 0.020" ABOVE the throttle body gasket surface and 0.005" - 0.020" BELOW the throttle body gasket surface ( see photo below).

It's important that the metering lever allows the inlet needle to close firmly under the full spring pressure, a flooding condition will surely occur if it doesn't. It also has to lift enough when fuel is drawn out of the meterming chamber to open the needle. If it doesn't, a lean condition occurs because the metering chamber cannot refill fast enough. To make things more complicated, OEM Walbro metering diaphragms incorporated the gasket whereas aftermarket types use a separate gasket. This allows an extra source of air leakage, variation in gasket thicknesses and variation in button heights. This has been one of the primary reasons rebuilt Walbros malfunction. This has been going on for years.

There are solutions to these issues. First, use a straight edge scale (on edge) and lay it across the metering diaphragm and gasket that you plan to use. I usually do this after I have laid them on the top of the fuel pump stack after rebuilding. This will place the metering diaphragm in it's relaxed state. Note the distance between the button and the scale (or the disk and the scale if it's buttonless type). You can use a feeler gauge if you need too but I have noticed that most aftermarket kits it ends up being nearly zero. Next, adjust the inlet lever above or below the throttle body gasket surface as needed to take up the distance you measured between the scale and the button (or surface of the disk). So in the case of the aftermarket kits that measured zero, you would place the arch of the inlet lever even with the gasketing surface of the throttle body. If the metering diaphragm that you plan to use is the buttonless type, you would have to raise the metering lever above the throttle body whatever the height of the button is (it's usually about 0.020"). The whole point here is to determine where the inlet lever height needs to be in order for the inlet lever to fully close under spring pressure and also for it to activate quickly when the metering diaphragm lifts. This was a little hard to explain, hopefully this makes sense?

The air leakage issue between the metering diaphragm and the metering gasket on the aftermarket kits usually is a non-issue. Even if they initially refuse to seal up well, after the gasket absorbs a little fuel, it softens and swells creating a good seal. Sealing ridges don't exist on the throttle body but they do exist on the metering plate in the fuel pump stack. The ridges effectively seal the metering diaphragm to the metering plate but they don't do a great job sealing the metering diaphragm to to the metering gasket. Of course, with the OEM Walbro metering diaphragms that were one peice, this wasn't an issue. If you encounter a particularly stubborn situation here, and you cannot attain a decent seal between the throttle body and fuel pump stack, a little Aviation Form-A-Gasket between the metering diaphragm and the metering gasket usually resolves it. You essentially recreate the OEM type by adhering the two. I have also had to occasionally flat-plate a throttle body that has had damage preventing a good seal.