Welcome to the seadoo forum. To solve just about any problem you could incounter, use the "Advanced search" option under my name and find a cure for the problem.The gray fuel lines are what is causes the problem. The lines deteriorate, and clog the small filters in the carbs. I have heard of people cleaning the carbs and not replacing the gray lines and the problem never clears up.
It is possible that the carbs aren't adjusted properly either. The High Speed screw is set to "0". These have a plastic cap on them to keep them from being turned any more than 1/4 turn. The Low Speed screw is set to 1 1/2 turns. The screw has a pin through it. If you need to adjust the idle speed do NOT use the low speed screws to adjust it. Use the IDLE Screw to adjust both carbs at the same time. When adjusting the carbs be sure both carbs are in sync.
Keep us posted on your progress.
Karl