Thread: Loss of speed

Results 1 to 17 of 17
  1. #1
    Member
    Join Date
    Sep 2016
    Location
    Garner NC
    Posts
    152

    Loss of speed

    Had my power head rebuilt a few months back. Ig is a carb 2.5l motor. We decided to remove the high compression head for stock heads to give the motor less stress. Also added 2" spacers to my 10" jack plate. I lost 10mph on my top end. I'm thinking my speed is lost by going to stock heads primary. Can adding 2" more setback provide more speed loss?
    2011 21xrd
    2011 250 Pro XS

  2. Member
    Join Date
    Mar 2005
    Location
    Wilkesboro, NC
    Posts
    865
    #2
    I would double check the timing and make sure it's reaching wide open throttle. There is no way dropping the compression a little will cause you to loose 10 mph. More set back should only help top end.

  3. Member crank68's Avatar
    Join Date
    Mar 2011
    Location
    Kenly, NC
    Posts
    17,416
    #3
    Did Jr at Pitstop build your mota ? Good guys over there.
    BULLET 20 XRD/250 Merc Sport XS
    www.ncboatguy.com

  4. Member
    Join Date
    Aug 2016
    Location
    Sardis Lake, S.E. Oklahoma
    Posts
    688
    #4
    Like Matt said, dropping the compression from changing heads won't drop top speed much if any, look for other problems, like a cyl down or linkage adjustment!
    Good Luck!!!
    20XDC Bullet/Modified Merc 260
    295TF Charger/Merc 225X-Sold
    20' Contender Pickle Fork/Merc EFI Bridgeport-Sold
    18' Stratus with Sommerford Tunnel Vee Hull/2.4 EFI Merc High Perf-Sold
    Freedom 240DLX Toon/Merc 115
    10' Cougar Cub/Merc 25 on the Bottle
    18" Homebuilt Tunnel/.021 OS Max Outboard on 50% Nitro with a Pipe

  5. Member alli ss's Avatar
    Join Date
    Jul 2004
    Location
    Greenbrier, Ar
    Posts
    7,921
    #5
    did you raise the jackplate? with the additional setback you'll need to raise it on up

    xpress x19, 200ho G2, aluminum sawtooth cut prop, paper sack tackle storage, ugly stik pro team, color c-lector

  6. Moderator 21XDC's Avatar
    Join Date
    Sep 2004
    Location
    Westland Michigan
    Posts
    63,351
    #6
    Shaved heads on my motor increased my speed by 1-2 mph... Increased compression by 10-15lbs I think.

    Marks Props 317-398-9294, 1850 East 225 South, Shelbyville, Indiana 46176 propellerman59@gmail.com http://www.marksprops.com/index.html

  7. Member
    Join Date
    May 2006
    Location
    Sturgeon Falls, ON
    Posts
    1,616
    #7
    First thing i would do is pull out all the plugs and see if there all burning even, Then if you got a hotfoot, get someone to press it while you check the carbs if there going wideopen.

    Does the motor seam down on power, like does it holeshot slower?

  8. Member
    Join Date
    Sep 2016
    Location
    Garner NC
    Posts
    152
    #8
    Hole shot is not noticeably different. I will check plugs and connections hopefully later today. I appreciate the feed back. I dont have access to a timing light and the plastic cover is gone that covers the fly wheel. How can I check the timing?
    2011 21xrd
    2011 250 Pro XS

  9. Member
    Join Date
    May 2006
    Location
    Sturgeon Falls, ON
    Posts
    1,616
    #9
    You can't change timing on those engines. ECU and flywheel are the only way to control timing.

    If you got a compression tester while your checking your plugs throw the tester in there to rule compression out.

  10. Member
    Join Date
    Sep 2016
    Location
    Garner NC
    Posts
    152
    #10
    It is pre ECU engine. I thought there was a way to adjust timing thru primary pick up screw or max spark advance screw.
    2011 21xrd
    2011 250 Pro XS

  11. Member
    Join Date
    May 2006
    Location
    Sturgeon Falls, ON
    Posts
    1,616
    #11
    Quote Originally Posted by cn8165 View Post
    It is pre ECU engine. I thought there was a way to adjust timing thru primary pick up screw or max spark advance screw.
    I meant CDI sorry. I'm not super familliar with that engine. I thought you could not adj timing as its picked up by the flywheel on the stator.

  12. Member
    Join Date
    Mar 2005
    Location
    Wilkesboro, NC
    Posts
    865
    #12
    You can adjust the timing on the throttle arm. The top of it is connected to the trigger. It’s not something you want to guess at though. If you’re not familiar with how it’s done then I would get a service manual for it or take it to somebody that knows 2.5s.

  13. Member alli ss's Avatar
    Join Date
    Jul 2004
    Location
    Greenbrier, Ar
    Posts
    7,921
    #13
    Unless somebody monkeyed with it the timing is not off. Those screws are marked with a glue to see if theyve been moved. Look for the things that have been changed- timing isnt one of them. You have to deliberately want to do that and its not easy. Look to see if your throttle is opening 100% and you never answered about raising your motor with the additional setback? A compression test and leakdown test will show if a ring is stuck or something

    xpress x19, 200ho G2, aluminum sawtooth cut prop, paper sack tackle storage, ugly stik pro team, color c-lector

  14. Member
    Join Date
    Sep 2016
    Location
    Garner NC
    Posts
    152
    #14
    Forgot to answer you on motor height. I had raised it up and it felt loose then I dropped it a click and it feels like it hooks up better.
    2011 21xrd
    2011 250 Pro XS

  15. Banned
    Join Date
    Nov 2010
    Location
    The 'Boro
    Posts
    6,179
    #15
    I'd listen to Matt on this one. He knows the 2.5's better than anyone I have ever met. The lower compression heads will show on holeshot, but will nort make a noticable difference on top end from my experience.

  16. Member
    Join Date
    Sep 2016
    Location
    Garner NC
    Posts
    152
    #16
    I had made a idle adjustment the wrong way. Got it back to where it was. See how it runs next time i get it out. I appreciate yalls input.
    2011 21xrd
    2011 250 Pro XS

  17. Member
    Join Date
    Aug 2016
    Location
    Sardis Lake, S.E. Oklahoma
    Posts
    688
    #17
    You certainly don't need to be turning screws on a 2.5 without knowing what yer doing! You turn the timing advance stop the wrong way and you've cooked it!
    20XDC Bullet/Modified Merc 260
    295TF Charger/Merc 225X-Sold
    20' Contender Pickle Fork/Merc EFI Bridgeport-Sold
    18' Stratus with Sommerford Tunnel Vee Hull/2.4 EFI Merc High Perf-Sold
    Freedom 240DLX Toon/Merc 115
    10' Cougar Cub/Merc 25 on the Bottle
    18" Homebuilt Tunnel/.021 OS Max Outboard on 50% Nitro with a Pipe