My friend has been paying a Marina to try and fix a surging problem on his 2 cyl engine. So far he has replaced the fuel tank (marina said that it couldn't be cleaned) replaced the filters,and injectors. Now the engine will start only some times, it cranks, but will not fire up. Other times it starts and runs. He has not run it long enough to see if it still surges.My question to the group is, do you think the problem is anything besides dirt, air or leaks in the fuel system? When running there is no black smoke that would indicate a clogged exhaust elbow. Any ideas???