correct on the full open setting. It should be just a couple of mm more than the restrictor. For Truggy I run Plus 4 c with 41021 header and 9853 pipe. This combo will produce the most power at the cost of runtime when compared to the 9901 and same header. I run the either the 7 or 7.5 mm depending on the track. Your needles will be around flush on top and in from flush about a full turn. These will get you close. This engine is more than enough for my truggy and I get great run time. 11 - 14 depending on the track.