I have a 25 'crest pontoon with a mercury 4stroke 115 efi. The engine and boat are 2003. I just purchased the package from down south and it had only 72 hrs. I drained all fuel and ran boat for 1st time. Boat ran very poorly. Went to dealer and the entire fuel system was replaced from tank to injectors. Old fuel had clogged everything. When I got back 3 weeks ago boat ran great. Full throttle put engine against rev limiter so a prop company recommended changing to a 13 3/4 x 15. This was done and full throttle can down to 5600. About this time I notice the tach start to jump slightly above 3000 and below 4500. The problem seems intermittent and whe it happens it seems the engine is "hunting" for an rpm. Never jumps more than 100-200 rpms. Seems to clear up and the engine runs great the rest of the day. Yesterday I went to boat and the problem was back but it did not clear after 1 hr of use. Boat will run great at or below 3k and above 4500 to max rpm but between 3k and 4500 it seems to have a slight miss. The mtr only has about 10hrs since all work done incl adding a external water seperator between tank and engine. I have done nothing to diagnose with the exception of filling fuel tank to very top and checking for obvious loose wires. I am thinking it may be a spark plug issue as i do not think the plugs were changed as part of the ful system replace. No signs of fuel in oil. Everything else is great. Mtr starts fine. Mtr has full warranty but I would like to try to fix if anything simple as it is a pain to pull and trailer to a repair facility. Please help.....
