Ryobi cs 30 why does the trim head turn on its own after started when I haven't touched the throttle !!

It is possible that the timing gear jumped a tooth. Take off valve cover and check to make sure timing marks line up. Other than that check other things like carb adjustment, good gas, air filter and other general tune up things.

Absolutely it can. Weight can slow it down, Friction can slow it down,. There are many things that will do exactly what you are talking but the #1 thing would be a Gummed up Carburator. EVERYONE is having the same problems right now.

May also be the clutch, in the drive section up by the motor. You will have to take it apart to inspect it

The arbor is twisted into

Are you using the proper size line? Check the ends of the spool. It will give you the size you need. Also while you are checking, locate the arrow that shows the direction to wind the line. Hope this is of some help...Lee

it sounds like the centrifugal clutch is slipping. take it to several shops and get some quotes. Most times you'll find that fixing a Ryobi is more expensive than buying a bnew one.

Here was my solution:
I was having problems with my ryobi cs30 weedeater also. It would start up fine on full choke, but i could not give it more than half throttle or ever take the choke off or it would stall out. I replaced fuel mixture, spark plug, spark arrestor/exhaust, fuel lines, cleaned carb, and still nothing! I was considering getting a better machine. Then i decided to play with the carb adjustments.(on my cs-30, they are two screws on the carb that have a "L" and "H" next to them) I dont think you can get the specialty tool for adjusting the carb unless you are a repair tech, so i just took a Dremmel tool with the circular cut-off wheel to the head of the specialty screws and made them into "flat-head" screws so i could adjust them with a regular screwdriver (if you dont have a dremmel, get one!) (As i was cutting into the head of the screws, i also cut into the casing protecting the head of the screws that was in the way, this does not cause any damage to the unit, that casing is only there to keep "un-certified" people from adjusting it for themselves.)
Now to the easy part: The "L" screw adjusts the idle fuel mixture and the "H" screw adjusts the full throttle fuel mixture. turning the screws clockwise make the machine run leaner (less fuel) and counter clockwise makes it run richer (more fuel).
-I started out by turning each screw 1/2 turn counter clockwise and started it up, then as it was idling, i started adjusting the "L" screw as i was moving the choke position to run, after a few full turns counter clockwise of the "L" screw, it was idling perfectly in the run position, then i did the same thing the the "H" screw while holding down the throttle and i got it to run perfectly in the run position. Now it is running way better than it ever has. I hope this helps everyone.
Good Luck!
* For this specific problem, i would say you should probably just adjust the "L" screw and hopefully that will help

Here was my solution:
I was having problems with my ryobi cs30 weedeater also. It would start up fine on full choke, but i could not give it more than half throttle or ever take the choke off or it would stall out. I replaced fuel mixture, spark plug, spark arrestor/exhaust, fuel lines, cleaned carb, and still nothing! I was considering getting a better machine. Then i decided to play with the carb adjustments.(on my cs-30, they are two screws on the carb that have a "L" and "H" next to them) I dont think you can get the specialty tool for adjusting the carb unless you are a repair tech, so i just took a Dremmel tool with the circular cut-off wheel to the head of the specialty screws and made them into "flat-head" screws so i could adjust them with a regular screwdriver (if you dont have a dremmel too, get one!) (As i was cutting into the head of the screws, i also cut into the casing protecting the head of the screws that was in the way, this does not cause any damage to the unit, that casing is only there to keep "un-certified" people from adjusting it for themselves.)
Now to the easy part: The "L" screw adjusts the idle fuel mixture and the "H" screw adjusts the full throttle fuel mixture. turning the screws clockwise make the machine run leaner (less fuel) and counter clockwise makes it run richer (more fuel).
-I started out by turning each screw 1/2 turn counter clockwise and started it up, then as it was idling, i started adjusting the "L" screw as i was moving the choke position to run, after a few full turns counter clockwise of the "L" screw, it was idling perfectly in the run position, then i did the same thing the the "H" screw while holding down the throttle and i got it to run perfectly in the run position. Now it is running way better than it ever has. I hope this helps everyone.
Good Luck!

Here was my solution:
I was having problems with my ryobi cs30 weedeater also. It would start up fine on full choke, but i could not give it more than half throttle or ever take the choke off or it would stall out. I replaced fuel mixture, spark plug, spark arrestor/exhaust, fuel lines, cleaned carb, and still nothing! I was considering getting a better machine. Then i decided to play with the carb adjustments.(on my cs-30, they are two screws on the carb that have a "L" and "H" next to them) I dont think you can get the specialty tool for adjusting the carb unless you are a repair tech, so i just took a Dremmel tool with the circular cut-off wheel to the head of the specialty screws and made them into "flat-head" screws so i could adjust them with a regular screwdriver (if you dont have a dremmel too, get one!) (As i was cutting into the head of the screws, i also cut into the casing protecting the head of the screws that was in the way, this does not cause any damage to the unit, that casing is only there to keep "un-certified" people from adjusting it for themselves.)
Now to the easy part: The "L" screw adjusts the idle fuel mixture and the "H" screw adjusts the full throttle fuel mixture. turning the screws clockwise make the machine run leaner (less fuel) and counter clockwise makes it run richer (more fuel).
-I started out by turning each screw 1/2 turn counter clockwise and started it up, then as it was idling, i started adjusting the "L" screw as i was moving the choke position to run, after a few full turns counter clockwise of the "L" screw, it was idling perfectly in the run position, then i did the same thing the the "H" screw while holding down the throttle and i got it to run perfectly in the run position. Now it is running way better than it ever has. I hope this helps everyone.
Good Luck!

pull the shat off the engine and check the inner shaft it sounds like its stripped or the theengine side is cracked hope this helps