The motor has been ported by kd rotary, and I know that ported motors run rough when could, but...the car seems to stumble when giving it throttle at idle in neutral, and then accelerate. Almost to the point as if it sounds like it's missing at idle. The motor was dyno tuned, but then I had to put a catalytic converter on to pass emissions. It won't pass the curb idle test on emissions. It will actually stumble then backfire, which makes me think the car is running to rich and the cat creates too much backpressure. Once the car reaches just off idle or 2000 rpm, it'll rev fine. I'd like to adjust air/fuel, but I don't know what to set it at, and am scared to lean it out too much. Any ideas would be more than welcome.