Echo 21cc Trimmer Mods (SRM-210SB, GT-2000, etc)

[mexicanyella]

I had some success on a muffler-modded 31cc Poulan Pro with a one-needle Walbro carb...It seemed pretty rich in the upper midrange and up top when the low-speed mixture was right, prior to the muffler mod. After the muffler mod leaned it out a bit (just drilled a few 9/64” holes aimed rearward to exit without melting the plastic shroud), it was better but still a touch rich. Running 32:1 got it about where it needed to be. Kind of the long way around the barn, but it was a dumpster-dive special and it has held up pretty well. It’s the backup to my backup now...kinda loud but reliable for four-five mowing seasons at this point.

Those upside-down Ryan/IDC/Ryobi/Poulan/Troy-Bilt engines, coming soon to a dumpster near you, are pretty crude but they seem to have pretty decent midrange torque...pretty handy for careful trimming around chain link fence or plants you care about. I’ve had several over the years and never had a problem with the cantilever crank or bearings. It’s always trimmer head or recoil problems, seems like, and the occasional carb
Kit. I seem to remember reading that the large-scale RC guys using them tried to keep them below 7500 rpm with prop size and pitch...so not in the same league of bottom-end robustness as modern pro grade trimmers, or even cantilever-crank 25cc Homelites.

Okay, digression over; carry on.

 

[Chris-PA]

My newer Echo 21cc trimmer has a ZAMA RB. The screw is called out as a main mixture screw in the diagrams. It does seem to do something, but it's not very sensitive. Next time I have it apart I'm going to try to figure out how the fuel circuit works and how that needle functions.

My stock 21cc with the RB carb does not have near as much power as the ported 24cc with a conventional carb, but it's not all that much less and it uses significantly less fuel. Also, with a cat muffler it stinks a lot less.