I have been running an OS 12CVR (3 port) in an Associated Gas Truck on the dirt oval for about a year. It was real simple to tune and seemed to have good power any time I pulled the trigger. Now I am running a Custom Works GSX sprint car on the dirt oval but using an OS 12TZ (5 port). The symptom I'm having is: especially when I've been pacing for about 2 laps at 1/4 throttle and I suddenly pull the throttle back fairly quick, the engine will emit quite a bit of smoke and then flame out. I am running the gear ratio other people are running with my type of car, but I'm wondering if the engine might be lugging when I get on it and thus flaming out. To get up to speed, I have take a straightaway or so to get on up to speed. It is better at getting up to speed after running about 2 or 3 laps at racing speed. Is this an indication of needing a little more gear or do I just need to change my way of building up speed after pacing? Once the car is running up to speed it seems to perform just fine. After about 5 minutes of running it comes off the track around 225 - 230 degrees. I've done the pinch test at idle and after about 2 seconds the rpm's start to increase. Oh, I'm using a P6 plug. Also, the 12TZ comes with 2 air inlets (5mm? and 6mm?). Is there a general rule of thumb as to which inlet to use? Right now I'm using the smaller of the two.