Who knows Walbro HDC carbs?

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So the carb/saw is running on all 3 transition ports in the carb, the L/M/H so as to burn all the fuel W/O flooding AND when the H port on the engine side of the carb loses little air the engine speeds up and is getting a better fuel air mix as the throttle plate starts closing.
Did you put the new PROPER SIZE check valve in your carb? (that you ordered)
I seem to remember that I used my mity/vac pressure/vac tester and I could test/confirm the forward and backward checking of the new check valve using a plastic needle tip adapter on a piece of tygon tubing gently held on the check valve and also confirmed some old carbs as checking ok. (but that does not totally confirm proper operation when checking and the engine running) A itty bitty piece of a knats bristle will hold the little valve open during operation..
If you have replaced the check valve and it's still odd

I would
TRY ANOTHER CARB.
 
So the carb/saw is running on all 3 transition ports in the carb, the L/M/H so as to burn all the fuel W/O flooding AND when the H port on the engine side of the carb loses little air the engine speeds up and is getting a better fuel air mix as the throttle plate starts closing.
Did you put the new PROPER SIZE check valve in your carb? (that you ordered)
I seem to remember that I used my mity/vac pressure/vac tester and I could test/confirm the forward and backward checking of the new check valve using a plastic needle tip adapter on a piece of tygon tubing gently held on the check valve and also confirmed some old carbs as checking ok. (but that does not totally confirm proper operation when checking and the engine running) A itty bitty piece of a knats bristle will hold the little valve open during operation..
If you have replaced the check valve and it's still odd

I would
TRY ANOTHER CARB.
Still waiting on the valve. Probably another week with my luck

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All HDC's have the rubber flap in the check valve. Some are different PN's (The HDC 39 calls for an 86-520 kit)

One carb that does use only a capillary screen are some of the Tillotson HS carbs.

The saw will not run properly without that little flap in the check valve. They are only missing if someone has been in there as they turn to a gooey black mess when they have failed.
Once you have that in, it might be easier to diagnose the issue.
Damn...i ordered the 86-523 kit

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Looks like the difference is the tan valve vs black valve

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Sounds good.

So the new check valve fixed the carb?
Them oiler bar guide plates sure can go south easily and evaporate. I've started saving and labeling my spare bar plates from old saws instead of just throwing them in a bucket.
I think maybe you can get by without the outer but the inner needs the slot so as the oil hole will stay aligned with the bar hole.
 
Sounds good.

So the new check valve fixed the carb?
Them oiler bar guide plates sure can go south easily and evaporate. I've started saving and labeling my spare bar plates from old saws instead of just throwing them in a bucket.
I think maybe you can get by without the outer but the inner needs the slot so as the oil hole will stay aligned with the bar hole.
It seems to have, yes. I tested the carb as per the above guide and it passed. Put it on and it tuned right in. The outer guide on this one acts as a block to push the oil up into the bar.

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Good to know that fixed it. So many problems with check valves, it would be nice if the kits would include them and leave out some of the bits that never have to be changed. When is the last time you changed the inlet valve, control lever, pivot bar and spring?
 
Good to know that fixed it. So many problems with check valves, it would be nice if the kits would include them and leave out some of the bits that never have to be changed. When is the last time you changed the inlet valve, control lever, pivot bar and spring?
I replace the inlet needle valve every time but never the lever or pivot.

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Good to know that fixed it. So many problems with check valves, it would be nice if the kits would include them and leave out some of the bits that never have to be changed. When is the last time you changed the inlet valve, control lever, pivot bar and spring?
Right
I think maybe I seen somewhere, maybe at the Walbro site for these type carbs that the check valve was not intended to be a serviceable item when the carbs were first available.
I've seen some posts on this site that talks about making the different size check valves using a leather punch. I think maybe the material in my kit looked like the tan flapper valve material gasket in some carb kits.
Here is couple links about making the valves and a video of Leon bench repairing and bench testing the HDC.
https://www.arboristsite.com/community/threads/repairing-walbro-check-valves.269276/#post-5117319

Here is a really good video of Lon flogging a Walbro HDC carb, how to carefully replace the check valve and other issues he encountered and bench testing.. About the inlet fuel barb being just pressed into the side of the carb also. I've seen instance on this site where the inlet barb got broken off in a vise.
https://www.youtube.com/watch?v=n16qcMctvnw&feature=emb_title
 
Right
I think maybe I seen somewhere, maybe at the Walbro site for these type carbs that the check valve was not intended to be a serviceable item when the carbs were first available.
I've seen some posts on this site that talks about making the different size check valves using a leather punch. I think maybe the material in my kit looked like the tan flapper valve material gasket in some carb kits.
Here is couple links about making the valves and a video of Leon bench repairing and bench testing the HDC.
https://www.arboristsite.com/community/threads/repairing-walbro-check-valves.269276/#post-5117319

Here is a really good video of Lon flogging a Walbro HDC carb, how to carefully replace the check valve and other issues he encountered and bench testing.. About the inlet fuel barb being just pressed into the side of the carb also. I've seen instance on this site where the inlet barb got broken off in a vise.
https://www.youtube.com/watch?v=n16qcMctvnw&feature=emb_title
Yep, a lot of us make the disc and the best material to use is the tan coloured "teflon" fuel pump diaphragm. However not too many people want to do this and it only works for the main nozzle check valve, if you have a saw with a separate primer bulb (not on the carb) there will be another check valve in the body low speed circuit and this one can't be removed without destroying it. Again, would be SO easy if they were in the repair kits.
 
I use cylinder shaped punches for making the discs, mount them in a drill press with a piece of oak board on the table. The slow speed rotating cylinder punch cuts a very , very clean disc so a pump diaphragm will make 8-10 discs easily ,keep them in a small marked plastic box for future builds. Its easy to pull the brass body out of the carb body without damaging it using a #6X32 machine screw will do for a one time removal, just turn it one full turn in so it does not bottom out on the carb casting below. A #6 x 32 bottoming tap will last forever, grab the shaft with pliers and pull the valve body out. The underside of the brass body will sometimes need cleaning up, may have black rubber transfered to it so I just rub it on a carborundum sharpening stone to polish it up nice and smooth.
 
I use cylinder shaped punches for making the discs, mount them in a drill press with a piece of oak board on the table. The slow speed rotating cylinder punch cuts a very , very clean disc so a pump diaphragm will make 8-10 discs easily ,keep them in a small marked plastic box for future builds. Its easy to pull the brass body out of the carb body without damaging it using a #6X32 machine screw will do for a one time removal, just turn it one full turn in so it does not bottom out on the carb casting below. A #6 x 32 bottoming tap will last forever, grab the shaft with pliers and pull the valve body out. The underside of the brass body will sometimes need cleaning up, may have black rubber transfered to it so I just rub it on a carborundum sharpening stone to polish it up nice and smooth.
Yeah, that's how I pull them out but the part of the orifice that seals to the disc always seems to get damaged, I'll just have to be more careful about the process and maybe spend some time polishing the seat end of the threaded hole. After breaking a tap, I've been threading it right through and then screwing in a machine screw to do the pulling with. Have to revise my procedure.
 
Yeah, that's how I pull them out but the part of the orifice that seals to the disc always seems to get damaged, I'll just have to be more careful about the process and maybe spend some time polishing the seat end of the threaded hole. After breaking a tap, I've been threading it right through and then screwing in a machine screw to do the pulling with. Have to revise my procedure.
I must be lucky as all the brass inserts I have pulled so far had a fairly thick bottom end to them, the thread of the machine screw barely makes a mark in the brass but holds strong enough to pull it out of the carb body. I did use a bottoming tap once but found the machine screw to be better to hold and pull the brass valve body out with. I made up a puller that a long nut on the machine screw can thread down the shaft and it applies enough force to pull the brass part out with little effort. Think of a steel bar 1/4" X 1/2" X 1.5 " long with a hole in the middle, thread the screw through the hole and then into the brass nozzle body , the bar spans the carb body resting on the outer rim , then just run the nut down. When it contacts the bar a couple turns with a wrench or pliers and the valve body pops right out undamaged. I found using a new machine screw each time gets a better hold on the valve body, I have lots of them in the screw assortment tray.
 
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