Bus is running sluggish. Checked it was firing on all 4 cylinders and it appears to be running on 2 only. The two that are working are nos 1 and 2 according to the diagram in the haynes manual or the two on the right as you look into the engine bay. Checked the plugs for a spark and all ok so am assuming its a mechanical problem .Just wondered if anybody knows what it could be. thanks.