There are no mixture adjustments thanks to our friends at the EPA, they are set at the factory for minimum emissions. If anything the machine should run better at high elevation due to the lean settings.

Thank you for your reply. This trimmer came with a warning that it is set for low elevation and must be adjusted before operation. I've found many postings about this and related Ryobi trimmers that have a symptom that they die when giving it full throttle and people explain that due to elevation. So, it should be adjustable. Also, I think it would run rich because of less oxygen at high elevation.

We also have a new Ryobi trimmer RY252CS and we purchased the pac-man tool. However, we can't find the adjustment screws either. Do adjusting screws exist on this machine? thanks.

No adjustment screws, I found out if you use high test gasoline and Amsoil Sabre at the 80 to 1 ratio it will run fine. Before anyone criticizes try it!

High Octane gas is not a benefit within either of theae engines it burns slower and hotter , which is detrimental to engine life . However Amsoi l Sabre is one of the best Syn 2 stroke oils on the market . I use it on various units from 50:1 to 100:1 ratio, s with exceptional results . No carbon issues what so ever , actual increased plug service life and no efuel issues . I would advise the Amsoil is the contributing factor of your success rate .These off shore comparatively low compression small engines can actually be damaged ( exhaust valve and head gasket ) failures due to continued high octane fuel usage .