ORIGINAL: skillet92
''Just one observation. The guys having the most trouble are the guys just coming up to speed with gas. Either there's a huge coincidence regarding those guys getting the engines with less than perfect reed valves, or this issue is becoming blown way out of proportion..... something typical of the internet.''
Agree on this statement. Most guys that are new to gas treat them like glow engines and always try to adjudt them. I tell them treat it like your chainsaw or weedeater. You put them away in the fall and get them back out in the spring and never touch the settings. At least i do. Gas engine are better at holding there settings than glow. I usually adjust before first flight and then only after break in. I have dles, evolutions, and zenoahs and all mine run great. I will be pulling the reed block on the 20 to check it as that one has some mid range burbling that i would like to try and eliminate.
Reed valves that are not sealing like they could are most often noticed when starting, or at low rpms. That mid range "burble" is about mixture. You can mess with the mixture if you want, but guys that have opened their plug gaps up to .024-.025 report noticable reduction in burbling over and over again. The wider gap helps burn that rich mixture better - no clue why, but it's about the easiest thing in the world to try?
There's another thought regarding the load on the engine - as in usually when this happens (the burble thing) it's lightly loaded. You NEVER hear about an engine burbling when vertical? Loading it with the next size bigger prop may help you out as well?