Evolution are not not cheap price wise and are a mixed bag both running and reliability wise. The gimmick is that the are supposed to be factory run in and adjusted and have metel tabs to keep you from adjusting the needle valves outside a proper operating range. Fact is they don't act like they have had any running time and the so called "Factory settings" may be good or may be so far out that the engine either won't even start or it won't stay running for more than a few seconds. This is no different than other engines except that the metel tabs may be in the way to adjust the needle valves to where they are supposed to be to get the engine to run properly. I have the 61 size and ordered a new TH 61 carb to replace the Evo carb to try and get this beast to run properly. As it is the engine has on occasion run well and with strong power but it is very intermittant and very unreliable. When you rev up you can see the needle valves start to turn from vibration which changes the settings! If the engine doesn't run well with the TH carb then I will be chucking the engine and keeping the carb. So far it has been a big dissapointment! [&o]