Carb Guru? WJ-69 and Clone comparison

[jmssaws]

Or if the butterfly is oriented like oem- notch on top or bottom

I've changed everything I can to no avail

 

[Chainsaw Jim]

I'd say check the valves to see if they hold a vacuum. If you don't have the tool then use a foot long piece of fuel line by mouth.
I just replaced a carb on an 056 that really compared symptom wise. I checked the valve and it wouldn't hold a vacuum for even a second. The replacement held a vacuum with no drop and now it idles and tunes like a dream.

 

[huskihl]

I'd say check the valves to see if they hold a vacuum. If you don't have the tool then use a foot long piece of fuel line by mouth.
I just replaced a carb on an 056 that really compared symptom wise. I checked the valve and it wouldn't hold a vacuum for even a second. The replacement held a vacuum with no drop and now it idles and tunes like a dream.

Is this the needle and seat you're checking or a different check valve? If so, how do you check it? I've got a wj39 on my 394 that is giving some of these symptoms

 

[Chainsaw Jim]

Is this the needle and seat you're checking or a different check valve? If so, how do you check it? I've got a wj39 on my 394 that is giving some of these symptoms

It's the main nozzle check valve. Here's a way to do it if you don't have the oem tool...
Remove the high jet screw and tighten the low side down lightly snug. Use a small piece of soft rubber to plug the tiny hole in the pan while you hold a piece of fuel line up to the open high jet hole tight enough to maintain a seal while you blow back and forth through it. The vacuum suction should hold the weight of the fuel line as it sticks to your tongue. You can also hold a mighty vac pump with a short section of fuel line up to the open hole to check it that way but it is a bit more challenging to hold it tight while pumping.
Here's a wj39...

 

[huskihl]

It's the main nozzle check valve. Here's a way to do it if you don't have the oem tool...
Remove the high jet screw and tighten the low side down lightly snug. Use a small piece of soft rubber to plug the tiny hole in the pan while you hold a piece of fuel line up to the open high jet hole tight enough to maintain a seal while you blow back and forth through it. The vacuum suction should hold the weight of the fuel line as it sticks to your tongue. You can also hold a mighty vac pump with a short section of fuel line up to the open hole to check it that way but it is a bit more challenging to hold it tight while pumping.
Here's a wj39...
View attachment 29010

Thanks Jim. I remember reading that now that you mention it. I'll check that before I reinstall the carb

 

[srcarr52]

Have we compared the low side needle to the OEM carb. I know we looked at the high side but I didn't see the low side.

The carb butterfly cutout should be lined up with two tiny holes in the carb bore, at idle the throttle shaft should be open enough that the butterfly points at the first hole (closest to nozzle). If the butterfly is past this first hole to get the idle RPM then the cutout in the butterfly needs to be bigger (more air bleed). The butterfly needs to be in front or pointing straight at this whole to create the low pressure zone to pull fuel. If it's past it's relying on the second hole and that is too far from the butterfly to be consistent. The first hole is for idle, the second is for off idle fuel enrichment (basically an attempt at a part throttle metering circuit).

You can also run it without the air cleaner and see if it's getting droplets of fuel through the main nozzle at idle. If it does, pop off pressure is too low or the nozzle check is bad.

Ekkk! I just looks at the pictures of the butterfly, the AM carb doesn't have a cutout at the idle circuit holes. Actually, I don't even see the idle circuit holes.

 

[Mastermind]

Ekkkk is right. lol

 

[Redfin]

So it probably is pulling fuel from the high at idle?

 

[Mastermind]

I've got one here.......it has idle, and transition holes, but no notch in the butterfly.

 

[Mastermind]

Now a real WJ69

 

[srcarr52]

So it probably is pulling fuel from the high at idle?

Who knows, without that cutout you have to have the butterfly open way too far. I can't tell if there is even idle circuit holes under from under the welch plug into the carb bore. There has to be something somewhere for the low side needle to do anything but I can't see it in the picture.

That cutout is to force the incoming air past the idle holes to atomize the fuel better. Also it acts as a small venturi, high pressure before the butterfly, low pressure through the restriction (cut out) and behind it where it can draw fuel in. If the incoming air isn't zooming past these holes the fuel puddles out and atomization is poor, idle is erratic.

 

[srcarr52]

I've got one here.......it has idle, and transition holes, but no notch in the butterfly.

View attachment 29030

I have seen carbs with holes before and after the butterfly, they rely on the high pressure system in front of the butterfly to push air into the low side circuit and mix with fuel and exit the rear hole. Those usually won't have a cut out on the butterfly unless the butterfly is getting too far open to get the idle RPM. Still that doesn't look like one, the forward holes are usually more spaced out or even before the venturi.

 

[Redfin]

If the incoming air isn't zooming past these holes the fuel puddles out and atomization is poor, idle is erratic.

Would this explain the higher idle needed to smooth it out?

 

[srcarr52]

Would this explain the higher idle needed to smooth it out?

Exactly!

 

[Redfin]

Riddle me this. Lots of carbs dont use these bleeds. How do they accomplish the same?

 

[jmssaws]

Riddle me this. Lots of carbs dont use these bleeds. How do they accomplish the same?

Easy rumplestilsken or as I call him crumpled for skin.
What's up john?
I'm fiddling with a wj34 that acts the same, I'll get a video of it.
Same problem as the am one

 

[Redfin]

What's up john?

Sitting here on hold with tech support trying to get my tablet going so I can pickup my next job.

 

[jmssaws]

Sitting here on hold with tech support trying to get my tablet going so I can pickup my next job.

Living the dream my freind.

 

[srcarr52]

Riddle me this. Lots of carbs dont use these bleeds. How do they accomplish the same?

Do you mean the cutout in the butterfly? Some carbs, like the husky 550 carb have a bypass bleed that has a need that can be adjusted. Great idea really.

Then there is the infamous EL46 562 carb that had idle and throttle response issues. The solution was to slightly enlarge the cutout in the butterfly and better align it with the idle circuit holes. This was fixed in the EL48. These are all auto tune carbs but the same principles apply, the computer is just automatically adjusting the L and H needles for you.

 

[Redfin]

Do you mean the cutout in the butterfly?

Yepper, thats what I meant. Thanks Shaun.