Angus,
I noticed when balancing a bunch of props, mine and a few friends, had about a dozen and started comparing, that the Menz is sort of a cheater. The 24x8 was really a 23-1/2x8, but the MSC's, Mezlik's, BME, NX and Zingers are all the same length as stated. May be part of it, take a look at your plug and see if its black, should be tan if mixture is correct. Can you see the tank when filling to be sure its full? I don't think I'd feel comfortable without getting at least 12 minutes to a tank. These fly so nice its easy to lose track of time!!