I purchased a B5hs but I will get a hold of a B6HS so currently I have 3 plugs..... LD Z4C(stock plug seems to be the best of the 3) Champion J8C( ehh....) and The NGK B5HS. I will purchase a B6HS, I also have my speed carb coming too so hopefully I'll see some smoother results, it seems like the stock plug performs the best...I ran the champion j8c...max speed was 25....crap..... Stock plug- 30-33 mph in that range, B5HS- havent really gone full boar because it's slippery, but the motor seems a TAD bit...rougher running. I don't know... I run a 20:1 mix and my next load of gas will be mixed with my synthetic stuff. I think I'm seeing different results because that champion plug is a range 8...so pretty cold, I have no idea what the range is on the stock plug or the B5HS. Should I try something else? I have a pretty accurate speedo due to keeping up in traffic. I have #41 chain(not that that matters) 44T Sprocket, performance chrome stack air filter...stock NT carb. 66cc 2-stroke. Runs like a champ! but I've had other all stock 66 cc motors with no upgrades that acheived greater speeds, another factor is my bike is a tad bit heavier than normal bikes but still..and I only weigh 120. So I have the speed carb coming as mentioned but I noticed different performance from different plugs so that could be it too, If I can reach a top speed of even 35 I will call it GOOD! I'd like to keep the 44T sprocket because it's a balance of speed/climbing power. Currently the stock plug is in. Any other suggestions would be nice, I know I'm going to hear(without port matching or changing sprockets, blah blah you can't really get more out of it) I just want to know what I CAN get out of it even if it's 2-3 mph faster that's all I want. nothing HUGE I don't want to go rippin' down at 50 mph, that's not my style. So let me know thanks a bunch guys! Oh give me an insight on that speed carb too. Has a red air filter(will be putting my chrome stack performance filter on, fuel shut off incorporated into the carb etc. Thanks!!!