I had ours every year for other maintenance and I kept looking at the end that connects to the manifold. It was as clean as a whistle! I thus mistakenly assumed that we weren't clogging... That and the fact that when we run the engine, I insist that we "push" it made me believe that there was no problem. The big tell tale for me was the soot on the transom. It was awful and fast getting worse. I just thought that the injectors were in need of maintenance.