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  1. #1

    Yamaaha 1200 PV engine stock compression and improved compression with a head

    What should the stock compression be of a 1999 Yamaha 1200 xl ltd when it was new... I know gauges will vary a little.

    Also can I add a performance head to increase compression without making changes to the stock carb settings? Also what kind of performance increase would higher compression give me?


  2. #2
    Head mod = more power = more fuel, so carbs would need to be jetted. The 155psi Head mod has been done alot but u see it more on the GPR's than the XLT's. Will the increased PSI mean it will be an arm stretcher, well no but it will be noticable. If you are looking for more power then the bolt on stuff is hard to beat....ie (RIDE PLATE, INTAKE GRATE, prop etc.) OSIDEBILL has a spec for the PV motors carbs (with stock air box removed and FA'S installed) that I just did for a friend and it was very noticeable in the upper RPM range.

    Also more compression equal more wear and tear these engines which are hand granades with the pin pulled anyways.

    Cant go wrong with the bolt on stuff and there should be alot out there on the used market for not alot of $$$.

  3. #3
    Thanks for the information...

    So which ride plate, intake grate, and prop would you recommend

  4. #4
    Quote Originally Posted by canon714 View Post
    What should the stock compression be of a 1999 Yamaha 1200 xl ltd when it was new... I know gauges will vary a little.

    Also can I add a performance head to increase compression without making changes to the stock carb settings? Also what kind of performance increase would higher compression give me?
    Stock compression is around 120. Increase compression to 150 only equals bottom end/accel. No need to rejet just run premium.

  5. #5
    800 grate if u can find one or a R&D. One of Jim's modded plate's are nice as well. Please don't make any engine mods without doing a rejet.....u will be one unhappy camper I promise u!!! Do a search for OSIDEBILL 12000 PV carb mod and buy some FA's. Cheap power.

  6. #6

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    My 2004 XLT went over 145 hours with a high compression head and NO rejetting. I used premium fuel and the extra compression improved power all thru the powerband including top end.
    However, at approx. 145 hours I decided to rebuild carbs and rejet and add F/S's using the standard O'Side Bills formula. I could not believe how much better the boat runs with the rejetting. So I am saying rejetting not needed, but I believe you get more from it than the compression in reality. DO both and you can be on the way to the numbers listed in my sig.
    You can use a 12/18 or 13/19 concord prop, you NEED a R&D scoop grate to keep from jetting thrown off (800 grate is a GPR item and does not fit), and a R&D ride plate with an angle cut will work wonders. Also upgrade to 2001-2005 XLT sponsons to get ride of the leaning to one side or other tracking the XLL does.

  7. #7
    Why take the chance on not rejetting is my point may or may not need it its all just an opinion, but it will be there and so will the piece of mind. its a fairly low cost upgrade and as we all know these motors are very particular.

  8. #8
    LT1GMC which high compression head do you use?

  9. #9

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    Group K modified stock head.

  10. #10
    Do you know what that increased your compression? 20 psi?

    Quote Originally Posted by LT1GMC View Post
    Group K modified stock head.

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