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Who knows Walbro HDC carbs?

RED-85-Z51

RED-85-Z51

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Got a Walbro HDC39 carb, starts okay, i can tach the top end out easy and the needle is very responsive to input.

Has absolutely no idle fuel that i can sense...ive soaked it, put a kit in it, gently blown it out with very low pressure air..nothing makes any difference. Needle almost out it will begin to fuel...just enough to to keep it from taking off. Case passed a pressure and vac test which surprised me.

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82F100SWB

82F100SWB

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Are you sure it's the carb? I have seen a few saws where the ring seal was bad and there wasn't enough impulse signal at low rpm/idle to keep the carb pumping.
 
RED-85-Z51

RED-85-Z51

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Check valve is probably bad.

never mind. They usually won’t idle at all if the check valve is bad
It really doesn't idle at all...i can just barely get it to the point it tips into the main jet and doesn't run away. Check valve the thing under the screen and small clip?

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Goinwheelin

Goinwheelin

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This may help.
 
SteveSr

SteveSr

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It really doesn't idle at all...i can just barely get it to the point it tips into the main jet and doesn't run away. Check valve the thing under the screen and small clip?

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Check valve is usually part of the main nozzle. If they stick open or part way open it will create an air leak and the saw won't idle.
 
RED-85-Z51

RED-85-Z51

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Pulled the check valve screen and found the check valve was entirely mia...no disc there under the screen at all.


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Okie

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I got some OEM check valves at a reasonable price over on flea bay sometime back. (with careful shopping)
I also seen a thread or two on this site about making the check valve.
I seem to remember their was maybe two versions or two different styles of the check valves.
Compare what's in your carb to the pictures of the replacements.
I also watched a video somewhere of how to gently lever out the old brass piece.
 
Old2stroke

Old2stroke

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Some of those carbs did not come with a disc under the fine screen, surface tension of the fuel on the screen was enough to provide the check valve function. All depended on how much isolation there was between the hi and low speed circuits. If you can get the right parts diag. it might show if there should be one. They are easy to make, just do a search on "repair a nozzle check valve".
When you cleaned the carb, did you poke a fine wire through the idle and transfer ports that were under the covering plug?
 
RED-85-Z51

RED-85-Z51

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Some of those carbs did not come with a disc under the fine screen, surface tension of the fuel on the screen was enough to provide the check valve function. All depended on how much isolation there was between the hi and low speed circuits. If you can get the right parts diag. it might show if there should be one. They are easy to make, just do a search on "repair a nozzle check valve".
When you cleaned the carb, did you poke a fine wire through the idle and transfer ports that were under the covering plug?

I havent seen an ipl yet that doesnt show a disc for an HDC. Yes the 3 ports were clear. Do you recall the spec for an hdc with no disc?

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stihl86

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Did you actually look at the condition of the piston and cylinder?
I’ve been fooled more times that I’d care to admit.
Till I got to the point of inspecting cylinder and piston
first thing on any saw repair.
 
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