I have a tvt 691 with the ohv carbs and arc flywheel. It starts fine. When I give it full throttle there is a dead spot just beyond the idle until about 1/2 throttle. Then it revs up but doesn't always pick up the second cylinder.  I have stock emulsion tube and stock jets. I have looked online but haven't Ben able to find any new blue emulsion tubes. I was told the this engine idles on one cylinder and then picks up the other cylinder at higher rpm. I'm new to this so any and all help would be great.