I'm working on a 10-year-old John Deere C1200 string trimmer (aka Ryobi UT20809). Wouldn't start at all until I replaced the ignition. Now it starts, but not with the choke on -- it will only start with the choke off but throttle held wide open. Once I release the throttle, the engine stays running OK (I adjusted the idle speed screw slightly to boost the idle RPMs).

Any suggestions on how to get it to start as designed with the choke on? This machine has a two position choke (on or off) and has the red and white plastic-headed carb adjustments screws (which I haven't messed with and am not quite sure how to adjust).

Thanks!