HELP! makita DCS460 dies when choke is opened

[bpmaas]

I'm stumped.
Symtom : engine dies when choke is opened (can only keep it running by holding butterfly almost closed). No amount of adjustment to high speed jet helps. Removed carb applied pressure to fuel inlet...holds pressure. Did a complete teardown of carb. Submerged it completely in fresh non/oxy gasoline for a day. Squirted gasoline into all passages, witnessed no blockages. Pump diaphram was good, so reused. Replaced metering diaphram. Replaced needle and spring. Reinstalled on saw...no change.
Deeper teardown: intake manifold, didn't find a problem. Put vacuum to the impulse hose, held. Fuel tank emptied and flushed. Replaced fuel filter. Tank vent removed, inspected (fine).
Mystery: with a full fuel tank (carb off) I can put the saw in any position, including upside down and fuel barely leaks out of hose. Apply a tiny amount of air to tank vent and fuel sprays all over?
I didn't check manifold with vacuum or pressure. I didn't check crankcase with vacuum or pressure.
The saw is super clean, in like new condition (I suspect very low hours).
Can anyone tell me what is likely the cause?

 

[Shane¹]

I see you mentioned you adjusted high speed. Did you adjust low speed at all? From what you described sounds like a carb issue still. But could be something else. Is the muffler plugged up? The coils on some of these saws went bad and would do some weird stuff but I would look at that last based on how you have described it

 

[cuinrearview]

What's it do with the air filter off?

 

[bpmaas]

I see you mentioned you adjusted high speed. Did you adjust low speed at all? From what you described sounds like a carb issue still. But could be something else. Is the muffler plugged up? The coils on some of these saws went bad and would do some weird stuff but I would look at that last based on how you have described it

Just the baseline. SSM says 1 1/2 turns out (that's where I set it). Didn't check muffler. Checked spark ...it easily will jump a 3/8" gap, nice blue spark (doesn't mean coil can't be bad).

 

[bpmaas]

What's it do with the air filter off?

All of the trials I did were with the air filter off. Which by the way looks brand new. Like the rest of the saw!

 

[Shane¹]

Id try opening up the low speed jet some and ideally swap on a known good carb

 

[cuinrearview]

Is the muffler a bronze color or silver? While unlikely, it's conceivable the cat in the later muffler could clog. But it still sounds like fuel delivery to me if the filter's good. The diaphragms in the right order?

 

[bpmaas]

Id try opening up the low speed jet some and ideally swap on a known good carb

I wish I had an alternate carb to use. This one a zama, has levers on throttle shaft & choke shaft that lock together when the choke is on. I suspect to aid in starting. The only spares I have are for Stihl saws.
I can try adusting the low speed jet.

 

[bpmaas]

Is the muffler a bronze color or silver? While unlikely, it's conceivable the cat in the later muffler could clog. But it still sounds like fuel delivery to me if the filter's good. The diaphragms in the right order?

The muffler is silver. The diaphram that operates the metering lever is on gasket first, then diaphram, cover. The diaphram with the valve flaps is on first, then gasket, cover.
Do you suggest removal of the muffler. I wasn't aware chainsaws had a cat in the muffler.

PS: I'll be away for a few days. I'll continue when I get back. Thanks for the responses so far!

 

[cuinrearview]

The muffler is silver. The diaphram that operates the metering lever is on gasket first, then diaphram, cover. The diaphram with the valve flaps is on first, then gasket, cover.
Do you suggest removal of the muffler. I wasn't aware chainsaws had a cat in the muffler.

Yours doesn't have one

 

[EFSM]

If it has a rubber main jet check valve, that could have swollen and plugged the man jet. But you said all passages were open, which I suppose includes checking from the high passage in the metering bowl through the main jet.

Does this carburetor have the plastic spacer outside the metering diaphragm for a pressure equalizer system (intelli-carb equivalent?)