i think there's a lawn equipment forum that would be a better place for help on that question.

Along with rustyJ comment all springs are made to certain tolerance. Meaning the height, diameter, and stiffness produced certain resistance. So measure your sping height. then stretch little at time to get the right resistance or spring pressure you desire to let the advance spool release one click at time when you lightly bump it. If you have to smack it on the ground usually the string will tie itself in knot and not release. If the spring is colasped enough it will release with the slightest bumping. So to make this short depending on the model and design. the spring has to be certain height to alow the right tension on the bump advance. Too weak (or Short) line comes out to easy. Too strong (spring height longer that it's suspose to be makes string hard to advance (providing the string is not knotted up on the spool which happens from time to time). All of us at one time or another has bumped it extremely harder thinking I didn't bump it hard enough when all it was the string became knotted and locked up on the spool reventing string advancement.

I feel the best would be hard to define or defend. I use the heaviest line and pre-cut it to give me a fixed dual line (with 2 knots inside the spool to hold it until itâÂÂs too short). I followed the suggestion of a Small Engine Dealer, Sales and RepairmanâÂÂs Advice (in about 2000). His info was based on facts on the Professional Yard Crews clients. He said Most Preferred the Mid Range Echo SRM-225 I believe at that time. He said that his were in the 220.00 range. Or! I could save a few dollars at Home Depot, Etc Big Box Store, with the same trimmer and two Year Warr then. I did and it starts today as easy as the guarantee then (2 pulls I think). Being honest it d/n solve my problem of breaking the string 8-10 times per my full small yard. The string problem was me personally IMO vs the trimmer. I like the straight shaft reach vs bending my back. I still use it in tight areas and guessed 3 hrs per yr but I feel itâÂÂs more like 6 hrs per yr (72 vs 36 hrs over 10 years at least trouble free and no replacements maintenance vs checking). My primary trimmer has a straight shaft, hard blade and wheel att. Due to all the concrete I have. Tilted at about a 45 degree, I bevel the grass to the dirt at the concrete and trim about every 3rd cutting. It is a modified Green Machine with a longer straight shaft to save bending my back.

I have an Echo GT2000 with the tap and go head and have no complaints. I use Echo's Rapidfire line and find it works the best of any I have tried. Some things to consider. A lot of the inexpensive curve shaft trimmer heads run very hot due to the poor lower end bushing. The heat is transmitted to the head and results in line 'welding'.The surface actually melts. Cheap aftermarket line is particularly bad. The line needs to be wound properly. Both lines are wound in the same direction. Pinch both between thumb and forefinger and rotate the spool with the other hand pulling the line to prevent twisting, don't wrap the line on the spool. The machine will work best at full throttle. The line is rigid and will cut most effectively. A lot of clutches have failed due to heat from slipping because the machine was run at part throttle.The clutch works on centrifugal force, the faster it turns the more force it exerts on the drum.