Hi, new to the forum, but have been happily using Stihl stuff for about 30 years, mostly chainsaws. Bought a new br600 a few years ago, figured even though it was a new design engine, Stihl would have it figured out, after reading thru a bunch of posts here, I guess they didn't. Run about 2 days a week, always used Stihl oil and fresh gas. Problems started when Florida went to E10 gas. First the oring on the gas gap would swell and after figuring that out replacing orings every few months cured that issue. Next the fuel lines deteriorated and leaked. Lately, it started properly, ran well for the first few minutes but never was able to hold full throttle, although the accelerater pump seemed to help the rpms. Air filter clean, valve adjustment good, cam timing right, good fuel flow to carb, good spark. Good compression, hot or cold. Fuel pickup never has been a problem for this one. Over the few years there seems to be a bit of oil seepage residue at the bottom of the engine, not sure if it;s a crank seal, but looks like it probably is. Presently, the gas tank gets pressurized even when just trying too start it, don't know if that is normal. Doesn't seem to be getting fuel thru the carb to the cylinder. I'm guessing the next step is to get a new carb. Don't know whether it is worth trying, am sort of dissappointed with this whole piece. Is the new style retrofit carb worth it and if so how much are they. This also has the broken backstrap mount. Also use another 4mix, an FS 110R, using the same fuel and only had the gas cap oring problem. The dealers around here are sort of clueless, they havent even heard of the Magnums. I just don't want to end up beating a dead horse. Maybe getting the biggest Stihl 2 stoke is a better fix. Any help would be appreciated.