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  1. #1
    mrbtd's Avatar
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    Air,Prop or Power for RPM's ?

    Ok. I am absoultely stuck @ a pultry 7020 -7080 rpms with the following mods.

    Ski = 2001 1200r

    Pro-Tec Open FA's with outerwears on 110/120 95g 7/8 out on low and 1 1/4 out on high - plugs look good if anything I could richen them up a bit

    150 lb compr head but using all 3 layers of the base gasket so I am getting 130lbs in all 3 on my cheapie gauge
    VF2 Reeds
    85mm Stock venturi (from a 1300)
    05 pump w 14/20 Dynaflt (stock)

    The boat runs hard and very crisp up to 68-70 I can squeeze 70.5 - 71 by moving back and down. But it runs a legit 69 in multiple directions.

    I need to find the other 150 rpm's
    Which do I do
    Repitch Prop ?
    Middle Layer of head gasket ?
    Change Venturi (Have a 87)
    Take the outerwears off.

    Index/JGapping will get me some but not 150 (Right ?)

    Please note with the seat off and front bucket off my rpm's did not change at all (my ears still ringing)

    Thanks in advcance.
    Last edited by mrbtd; 05-09-2007 at 08:10 PM. Reason: forgot about the reeds


  2. #2
    MR. SCOVILLE UNIT SUCKMYWAKE's Avatar
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    i'm thinking the dynafly might be a little too much for the 1200cc. some of the stock 1300's have a hard time pulling it. and remember, it more than likely is not a true 14/20. it could be high or low

  3. #3
    You're turning a lot of prop, especially with the 85mm nozzle. You need to slightly de-pitch the prop and or go to the 87mm nozzle.

  4. #4

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    If it was mine, I'd add more power, by 20lbs more compression, and look into some type of an ignition upgrade ( keyway or advent) These two things could potentionaly add 100rpm+ Try the 87mm nozzle and see how you like.

  5. #5
    Moderator RX951's Avatar
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    * Do not depitch that dynafly, you will decrease the O.D. of it and end up with too much clearance between it and the wear ring (pump liner)

    * What kind of TACH are you using ?

    * I would get another good compression guage and get a second opinion of compression numbers.

    * You can also add an 87 mm nozzle and pick a few more RPM's.

    * Are you running the OEM powervalves ? if so, you need to check and make sure they are opening all the way.

    * I run outwears on my carbs. Your still missing some RPM's somewhere.

    * Do you still have the chokeplates in the carbs ?

    * Was that prop brand new out of the box ? If not, you need to recheck the pitch on it.

    * With the mods you have, you should be able to run about 72/73 easy with the stock ignition. given you have about 150 more rpm too. The stock ignition can take you pretty far. I have the OEM ignition on my unported 12R

  6. #6
    Happily Self-Employed WFO's Avatar
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    Try a little at a time.

    Lose the outer wears and put on the 87mm nozzle.

  7. #7
    just GOT TO DO IT! great lakes gpr 1200's Avatar
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    "You're turning a lot of prop, especially with the 85mm nozzle. You need to slightly de-pitch the prop and or go to the 87mm nozzle."

    I don't know a darn thing, but I do have 87 nozzle if it would fit you could try it? I put it on e-bay but dought it will sell, If it does not I shipp it to you?

  8. #8
    Moderator RX951's Avatar
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    Quote Originally Posted by great lakes gpr 1200 View Post
    "You're turning a lot of prop, especially with the 85mm nozzle. You need to slightly de-pitch the prop and or go to the 87mm nozzle."

    I don't know a darn thing, but I do have 87 nozzle if it would fit you could try it? I put it on e-bay but dought it will sell, If it does not I shipp it to you?
    PEOPLE, Again, do not depitch a dynafly, you will end up with too much clearance betweent he pump liner and prop. If it were a concorde, no problem, but a dynafly with lose O.D. if you depitch it !

  9. #9
    Moderator RX951's Avatar
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    Quote Originally Posted by mrbtd View Post

    Please note with the seat off and front bucket off my rpm's did not change at all (my ears still ringing)

    Thanks in advcance.

    yup, I noticed the same thing too a few years ago.

  10. #10
    mrbtd's Avatar
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    Wow guys...I really appreciate all the help.

    Prop/pump came used from a board member - Carl @ island touched it so I believe it is a true 14/20

    I will get the power up rather than repitch the prop.

    I figure I am not going to hurt anything by trying the 87 so it is going on for the next run.

    For the PV's I did verify they were set correctly by using the 4mm allen wrech through the side. My couplers were terrible sloppy so I put on the wave eater couplers and everything seems to be operating ok there.

    The ski has 73 hours and the PV's have never been cleaned could that be stealing a little ?

    Using a commercial tiny tach to get the rpm's.

    I will also get another gauge to verify the compression (this would be the third one) All have been 131-132 ish. Does the 1 layer of gasket make that much diff.


    When we talk about compression very little is said about squish is it not relevant ?

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