Husqvarna 576xp throttle problem?

[bettio]

Hi all, I have a strange problem with my 576xp. When the saw is running, the throttle will stick open slightly and seems to stick open for random amount of time. It will return to idle after a second or too and sometimes sticks until I tap side of the saw. When the saw is off it won’t do it at all. I have removed the throttle cable and had the saw running and pushed the throttle linkage by hand and it will stick open slightly then return?? Any ideas?? Have the cleaned the linkages and still the same.  Strange as only does it when running, would this be blow-by causing it? Any help is appreciated thanks 

[Muddy42]

Could there be dirt in the throttle control on the carb or the idle screw, or the butterfly valve etc.  Have you tried firing in lots of carb cleaner? You might need to take the carb off to clean and check everything.

[spudulike]

Interesting diagnosis..."blow by", not a term often used!! It usually kills idle and causes puffs of fuel vapour out of the inlet manifold if you grab the throttle!!

Anyway, if you have manually closed the carb throttle linkage and it still does this holding on to revs thing, it sounds like an air leak to me so looks like a full pressure and vacuum check is needed to me.

It is possible the manifold to cylinder union is leaking or a seal has gone. I believe there was an issue with this saw model having crank bearings spinning in their seat...ADW will come around soon and add a bit of extra to my diagnosis.

[adw]

You right Steve they did have some issues with the drive side main bearing spinning in the crankcase, remove the sprocket and clutch, grab the end of the crank and see if there is any up and down, if so it’s not good, a side thought is the short link rod between the throttle shaft and x torque valve, I have seen these get hung up and not close the valve properly even though the throttle shaft is completely closed.

[bettio]

Thanks for all the replies. I stripped the carb off and gave it all a good clean and on reassembly noticed excessive play in the metal choke pawl on the shaft. This seems to sit against the throttle cable holder at a certain point, excuse my terminology, hope the video helps. Manage to squeeze it gently with pliers and has helped. Guessing with the saw running the vibrations caused it to move over and would explain how I couldnt replicate the issue non running. Haven’t used the saw running as too late but will update the post if needed, thanks all.