I have one fitted to my BEC, but it has a separate on/off switch in the power feed. When you're going slow, or in traffic, you'll be using the clutch as normal, so don't want the ignition to cut out. Sounds like it may be set up wrong, with too long a cut out allowing too much unburnt fuel to build up. Mine's set for milliseconds, just to unload the gearbox when you're pulling back the gear lever, but the timing must be right. I don't tend to use mine much, as I prefer a quick throttle peddle lift to do clutchless upshifts. Does your's blip when going down the box? Probably no harm done. What exhaust can do you have? Clive.