I have a 96 seadoo Challenger. I put a 787 motor from SBT it and I cant get it to run. When I set the rotary valve to where it is suppose to be set it just backfires out of the carbs. I can turn the rotary valve one click counter clockwise and it will start and idle but wont take any throttle. I also hear a bad vibration in the jet pump while it is idling but that could be where it is running rough. Any ideas where to look would be greatly appreciated. Thanks