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  1. #1
    Member
    Join Date
    Oct 2014
    Location
    Clearwater FL
    Posts
    827

    Optimax puff of smoke/rpm surge on startup

    2014 300xs Motor Serial 1E052216 RPM: 5450-5900 depending on load and which prop I am running. Props: 25 and 26.5 bravo xs. Merc monitor gauge. Premium plus oil

    Sportsmaster lower

    Went out fishing today and did some idling around trolling for grouper (mostly under 1k rpm or 4-5 mph). Normally if I do extended idling it will just puff a little smoke on takeoff. The motor started to have a rougher idle and would occasionally die when being put into gear. When starting up, it would usually give a little puff of smoke and the rpms would surge up a little bit like it had excess fuel.

    Thoughts? Motor runs great at all other speeds but the idle is a little rough now.
    2007 Sterling 22xs-Yamaha 250-Dual 10 foot blades-Ipilot-Bobs Jack plate-HDS 8 (SOLD)
    2016 Sterling 220XS: (SOLD)
    2008 SCB Topcat 250 XS (SOLD)
    Current:
    2014 SCB Stingray Sport Merc 300XS
    2018 ES Custom Revolution 25 Merc 400R

  2. Member
    Join Date
    Aug 2012
    Location
    Carthage MS
    Posts
    221
    #2
    That's the way my issues started with my 2016 250pro xs at 30hours. After about 5 more trips I was running and came off plane and engine shut down wouldn't crank. Pulled cowling off and it was squirting gas everywhere when trying to crank. It was a busted fuel regulator diaphragm on fuel rail. Dealer replaced been fine ever since.
    Greg Wood
    2016 Ranger Z521c 250 Optimax Pro XS
    Dual Power-Pole Blades 10ft
    Lowrance HDS 12 Gen3's at Console and Bow

  3. Member
    Join Date
    Oct 2014
    Location
    Clearwater FL
    Posts
    827
    #3
    For those wondering, it ended up being the fuel regulator diaphragm that was causing the issue.
    2007 Sterling 22xs-Yamaha 250-Dual 10 foot blades-Ipilot-Bobs Jack plate-HDS 8 (SOLD)
    2016 Sterling 220XS: (SOLD)
    2008 SCB Topcat 250 XS (SOLD)
    Current:
    2014 SCB Stingray Sport Merc 300XS
    2018 ES Custom Revolution 25 Merc 400R

  4. Mercury 3L/4 Stroke/Verado Moderator EuropeanAM's Avatar
    Join Date
    Apr 2008
    Location
    Greenville, SC (US)
    Posts
    94,945
    #4
    Thanks for updating with the cause- that's very plausible.


    Dual Mercury Master Technician- for Mercury Outboards, Mercruiser and Mercury Racing at European Marine in Greenville, SC.
    Still consider myself a "Marine Apprentice" after 47 years (learn something new every day).
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