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  1. #1
    Member
    Join Date
    Jun 2004
    Location
    Albany, IL
    Posts
    172

    2018 SHO 250 Stumbles every cold start

    Hi All, every time I cold start the motor(not being used for 12 hours or more) it fires right up, runs perfect for about 3 seconds, then stumbles and almost dies for a couple seconds while still in neutral, then begins to run smoothly again. It may die if I put it in gear while stumbling. The rest of the day, it starts/runs perfectly. Note is runs great, zero performance issues.

    It just started doing this a few months ago before 300 hour service(around 270 hours). Then I hit 300 hours and I went ahead and did the 300 hour service. It actually ran perfect the next couple times out after that, but has since started the exact problem again(my guess is because I primed the fuel system after replacing front engine fuel filter and vapor separator filter). I have tried several things- 1)Prime bulb before startup 2)Turn ignition ON for several minutes before cold start to let fuel pump run more 3)Open fuel cap on boat to remove a possible vapor lock.

    My next thoughts are replacing fuel line/primer bulb between engine and Vapor separator filter OR VST Filter???

    Looking for some suggestions!

    Thanks!
    Last edited by gr8basser; 11-07-2022 at 02:02 PM.
    2018 X21 Pro
    Yamaha 250 SHO
    12" Hydraulic Atlas
    Minn Kota 112# Ultrex

  2. Member
    Join Date
    Jun 2004
    Location
    Albany, IL
    Posts
    172
    #2
    I do also notice the primer bulb loses its prime after about 2-3 minutes after squeezing til its hard. Same result even if the key is ON. Anyways, as all hoses/clamps are tight/no leaks between gas tank and primary fuel filter on front of motor, for good measure I am replacing the primer bulb this week and see if the prime changes. Can any of you confirm if your primer bulb stays hard all the time on these motors?
    2018 X21 Pro
    Yamaha 250 SHO
    12" Hydraulic Atlas
    Minn Kota 112# Ultrex

  3. Member
    Join Date
    Aug 2005
    Location
    St. Charles
    Posts
    2,536
    #3
    Primer bulb is never hard and I was told not to squeeze it as it was not necessary being a fuel injected motor. Haven't touched it, and haven't had any issues.

  4. Member
    Join Date
    Oct 2016
    Location
    Santa Cruz, California
    Posts
    316
    #4
    Quote Originally Posted by gr8basser View Post
    Hi All, every time I cold start the motor(not being used for 12 hours or more) it fires right up, runs perfect for about 3 seconds, then stumbles and almost dies for a couple seconds while still in neutral, then begins to run smoothly again. It may die if I put it in gear while stumbling. The rest of the day, it starts/runs perfectly. Note is runs great, zero performance issues.

    It just started doing this a few months ago before 300 hour service(around 270 hours). Then I hit 300 hours and I went ahead and did the 300 hour service. It actually ran perfect the next couple times out after that, but has since started the exact problem again(my guess is because I primed the fuel system after replacing front engine fuel filter and vapor separator filter). I have tried several things- 1)Prime bulb before startup 2)Turn ignition ON for several minutes before cold start to let fuel pump run more 3)Open fuel cap on boat to remove a possible vapor lock.

    My next thoughts are replacing fuel line/primer bulb between engine and Vapor separator filter OR VST Filter???

    Looking for some suggestions!

    Thanks!
    Has the engine been flashed with a performance tune?
    David Patten
    Automotive and marine technician.

  5. Member
    Join Date
    Nov 2010
    Location
    Salisbury, NC
    Posts
    453
    #5
    You notice the primer bulb loses it's prime. A good place to start, replace it and the fuel line. That bulb should always be tight. Good luck, keeps us BBCr's posted.


    RangerZ - IONIC Batteries, Lithiumhub.com

  6. Member
    Join Date
    Mar 2006
    Location
    Maine
    Posts
    3,368
    #6
    Quote Originally Posted by clayshooter100 View Post
    Has the engine been flashed with a performance tune?
    Interesting...Does having a "Flashed" ECM change the starting or idling characteristics? If so I have never heard this mentioned anywhere before.

  7. Member
    Join Date
    Oct 2016
    Location
    Santa Cruz, California
    Posts
    316
    #7
    I have seen several engines with the Nizpro tune that exhibit the exact condition mentioned here. It seems that their baseline starting map causes the engine to run overly rich for a few seconds when cold. The engine then self corrects and runs fine. I haven't seen any issues because of this, just a bit annoying.
    David Patten
    Automotive and marine technician.

  8. Member
    Join Date
    Jun 2004
    Location
    Albany, IL
    Posts
    172
    #8
    Thanks Clayshooter.
    UPDATE: I've been in discussion with Nizpro over the last several months on this and they're unaware of the issue. There's 2 software versions available for this ECU flash, V1 and V2. I'm on V2 originally set to 6200 limiter, I had Nizpro flash to 7100 limiter and no change in symptoms. Still stumbles or dies after ever cold start after not starting for at least 12 hours. After that starts perfectly the first time every time.

    My workaround to prevent possible spark plug fouling as the stumbling does richen up the cylinders badly.(noticeable black smoke on 2nd start if it dies) For cold start only:start the engine and immediately turn off the key. Then immediately start the engine again. No stumbling this way. Rest of day continue starting per normal.

    Hope this helps anyone having this issue.
    2018 X21 Pro
    Yamaha 250 SHO
    12" Hydraulic Atlas
    Minn Kota 112# Ultrex