Husqvarna 550xp carb fix

[idiotwithasaw]

My 550xp was giving me a little trouble, it was having an off idle bog/ slow throttle response, and would die if left to idle for longer than 30 seconds. Then required several pulls of the rope to bring it back to life, almost like it was flooding itself. Needless to say I was a little disappointed in the performance. If this was a normal carburetor most people would just lean in the l screw and go from there, but this being an autotune there are no screws to turn... Or are there. this little guy is hiding behind a brass plug masquerading as an accelerator pump.

I remembered reading a thread on Another Site about this little guy, it was never really cleared up to me where it went or what it's for, if someone else knows please chime in for all of our benefit. Anyway it was suggested that this screw be turned 1/4 turn CCW and that is what I did.

After reassembling I took it out and did some cuts and got it warmed up to operating temps then let it idle for several minutes without issue, it didn't die once. It also had throttle response you would expect out of a pro grade 50cc saw. I then let it set for a short while +/- 10 minutes and it started one pull low idle. In my lowly opinion this has fixed my problem.

This was on a walbro AT-1A carburetor, the one in the picture is a walbro AT-1 off of a 545, BUT essentially the same carb with different programing I believe.

 

[CR888]

Well done! Many dealers would fail to diagnose and fix that issue, most probably just replace the whole carb. Hope it stays running well, though I do wonder as it is still just a plain ol carb, how it did run well then had issues and after adjustment of the hidden holy grail screw came good again. What I mean is what changed making it need adjustment? I would love the Husky carb sercvice pdf for the new AT carbs.

 

[idiotwithasaw]

One thing I did notice the screw had almost no resistance when I turned it. And I found a video by @KenJax Tree where he removed it and it didn't have a spring for resistance just an o ring, my guess is that over time that little screw vibrates out of position.

Another thing, while I have owned this saw for a while I haven't used it a lot until yesterday, but it seems like it has always had this problem since I owned it.

 

[David Young]

nice work Ben,
Can you adjust it while its on the saw or do you have to remove the carb?

 

[idiotwithasaw]

Unfortunately the air horn must be removed to adjust it, however the carb can be left on.

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[psuiewalsh]

Anyone have the base setting? If it is turned in how far do you back it out? Someone said it is an air bleed so the more you open it (CCW) more air. I have similar issues on mine as well and did the same but have not cut with it to truly test.

 

[idiotwithasaw]

I wonder what the symptoms would be if it was turned too far out?

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[Simondo]

Did you have to drill a little hole and pull the plug with a screw ?
How did you go about replacing the brass and do you think the reset screw will stay put if the brass wasn't put back .

 

[TJ the Chainsaw Mechanic]

Good stuff to know! Thanks for posting!

 

[idiotwithasaw]

I attempted to remove it without poking a hole in it so I could reuse it, but I wasn't successful. However I don't believe the plug actually held the screw in place because when I tapped on it it went deeper into the hole, so it's not touching the screw anyway.

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[Simondo]

I attempted to remove it without poking a hole in it so I could reuse it, but I wasn't successful. However I don't believe the plug actually held the screw in place because when I tapped on it it went deeper into the hole, so it's not touching the screw anyway.

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File this one under … "For future Reference "
Thanks

 

[idiotwithasaw]

Just be aware, I'm just a hack trying new things and experimenting and sharing my results. I am in no way an expert, or a trained chainsaw mechanic. May cause impotency, blindness, inner earworm deficiency, squat cobbling, and general sense of phroo phrooeyness So your results may vary. Ok end of the required disclaimer.

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[Stihlbro]

Just be aware, I'm just a hack trying new things and experimenting and sharing my results. I am in no way an expert, or a trained chainsaw mechanic. May cause impotency, blindness, inner earworm deficiency, squat cobbling, and general sense of phroo phrooeyness So your results may vary. Ok end of the required disclaimer.

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Good one!!!

 

[Simondo]

Just be aware, I'm just a hack trying new things and experimenting and sharing my results. I am in no way an expert, or a trained chainsaw mechanic. May cause impotency, blindness, inner earworm deficiency, squat cobbling, and general sense of phroo phrooeyness So your results may vary. Ok end of the required disclaimer.

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Hey …someone has to take the first leap ... there is always more to get to grips with on these saws.

 

[psuiewalsh]

I played with mine again. It seems like one turn out is a good setting to start with on the screw. I tested the saw for leak and it did not move after 10 minutes. Vac tested the fuel line and same. No leaks. Put on a different carb I had purchased. No issues. Maybe at some point I will go back and try the old carb again. For now I need some long term evaluation of the newer carb. I checked the lever heights in the carbs. They both appeared above flush with the center of the casting. My W gauge does not cover this series so not sure what the measurement should be. Last question is the valve sheet in the carb. It is the blue plastic type. I thought that in the past these were not good for the 199's anyway.
Thoughts?

 

[idiotwithasaw]

How did you block it off for the vac test?

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[Keith Gandy]

How did you block it off for the vac test?

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Rubber between carb/intake and between cylinder/muffler and adapter through sparkplug hole

 

[psuiewalsh]

In this case i bought the stoppers and plates from husky. I think it was $25 or so.

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[psuiewalsh]

On this saw you would really need to make stoppers and plate on intake due to secondaries on carb

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[idiotwithasaw]

It's kinda hard to imagine a way to block it all off without the factory tools

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