Husqvarna 50 Rancher chokes itself out without extra throttle

[lot_lizard]

I need some help from the elder gods on this one. I have 7 mid-90s to early 2k Huskies (5 are XPs), older McCullochs, etc. Only saying because I am new to forum but not this hobby, and all run like tops with frequent maintenance. I had the opportunity to pick up a gem mint 1984 silver tagged white top 50 Rancher that has MAYBE been started a handful of times in its life. I am a newbie to this carb.

It starts/runs great if I give it throttle, but the butterfly immediately chokes the engine out if I don’t give constant switch pressure. The throttle screw is pegged all the way down, but still doesn’t give enough air to keep idle or start on its own (not even a crack of daylight). I would be SHOCKED if this wasn’t the stock carb given how pristine the inside of the this top cover is (the original air filter looks brand new, and he said he never replaced it once), but I haven’t verified numbers on the carb. Needles (L/H) are where they should be and runs great throughout the power band. What am I missing?

There is no independent choke on the carb itself (this part is new to me... it’s that silly air filter vacuum seal from pressure by the top lid itself). I have the top off for this exercise, so the “odd” choke is a non-factor. I don’t see any additional butterfly or throttle adjustments possible. Again... What am I missing? I really don’t want to take it apart because it really is “as new”

 

[rupedoggy]

Have you tried it without the air filter?

(L/H) are where they should be and runs great throughout the power band.

What does this mean? Is it running well or not? Your explanation is full of contradictions for me.

 

[lot_lizard]

The high is perfect. The low I believe is good if I hold the throttle speed at 2500 rpm. Sounds flawless between 2.5k and 12.5k. The idle screw does not keep the throttle open enough to maintain 2.5k rpm even if fully seated. I have to keep pressure on the switch. I don’t see the contradictions, but I agree it is odd

 

[lot_lizard]

Have you tried it without the air filter?

Missed this before... apologies. I have had it off the whole time to observe the throttle body. The throttle body shuts completely if pressure isn’t applied manually to the switch in addition to the throttle screw being fully seated. I can only assume something is bent too much on the point of contact between the throttle screw and the exterior plate it comes into contact with?!?!

 

[Huskvarna hotellgäst]

The idle speed screw should allow quite a wide range of adjustment so if the throttle disc and shaft don't rotate as you adjust I'd say there's a misalignment somewhere.
If the throttle disc and shaft does rotate as you adjust the screw but it makes no difference, check that the throttle disc isn't reversed
If one of your other Huskys has a Walbro HDA you could try that just to rule out air leaks or something else.

 

[lot_lizard]

thanks @hotellgäst... I really think the throttle disc you mention must be out of line somehow. So bizarre. I'll run it down. I am beginning to understand why this saw has never been run though

 

[rupedoggy]

OK I think I have some of your lingo down now and will try to help. I believe the thing you are calling the throttle body is what I call the throttle plate or butterfly. If your throttle screw is all the way in and still the butterfly is closed, the shaft may be twisted of maybe loose on the linkage. Look at the picture and see the end of the throttle shaft. It should be tight and not allow movement with the linkage. If loose tighten up with a small punch or put some JB weld on it and fix.

 

[lot_lizard]

thanks @rupedoggy.. the pic is a big help