I'll be honest all of my Magnums run great. The only problem I had was with this 70 that had weak springs and you couldn't get any top end. Hobbypeople replaced the springs, tuned it up and it ran great. Then I didn't use it for a long time and one of the valves stuck open, so no compression. When I tried to free the valve up the valve keepers came off and I couldn't get them back on. I even called Hobbypeople and they sent me their instructions and how to put them one. Even said they could do it. Well then I lost a spring and called them again. that's where the problem began.