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  1. #1
    cmgww's Avatar
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    Man, I am fat....and my ski is running rich too

    All weight jokes aside (I need to lose a few, nothing major but I am getting snug in the britches)...

    My ski is running really fat/rich. Before this past Thursday (85 and high humidity) I last rode just after Memorial Day (low 70s, low humidity, cold water). I've been riding long enough to know that weather plays a huge factor with 2 strokes. Maybe it's just the time away, busy with a new son, but my ski felt dog slow a few days ago. And no, I didn't gain a bunch of weight in that month off the water, lol.

    I am running 155 jetting on OE carbs (rebuilt), on a Lowell ported engine. It's a bit on the rich side, that is sure, but it is bc we seized a piston on the original 1390 build, just after break-in. We originally had 145s. In hindsight, I think the prop was to blame. It was really steep, Solas DF repitched to 15/28 or something ridiculous, I can't remember exactly. I think it was too much for the engine and it was loading too hard. We got the top end rebuilt and put a 14/23 loaner from OSide Bill (RIP) and were taching around 7350 with great holeshot and mid range. We also put on a 2nd fuel pump and air separator to prevent any leaning out. Had to give the prop back, and am now using the Solas repitched to 15/24 (maybe? Can't remember the damn prop pitches!)

    My brother's 1390 is nearly identical except it's a GroupK build with a little leaner jetting, and it's running great in these temps.

    Should I jet down to 150? I know I need a less steep prop too, haven't tached it in a while, but I know it's not where it should be. I could hear it on the last ride. Even the digital gauge was barely touching 7000 RPM. I am thinking a 14/24 or so would be just about right.

    I got 77.7 MPH out of my current setup in mid May. But I hate to lose so much when it gets hot out, which it is now. It's even dying during idle speed, which it hasn't done before (probably need to bump up the idle speed screw)

    i think I can still get 80 out of this ski in the right conditions, but I definitely don't want the power loss I am experiencing in the higher temps. I know some is inevitable, but this was night/day bad.

    Any help would be much appreciated.


  2. #2
    you shouldnt have to rejet for weather, thats what the t handles are for.

  3. #3

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    His high speed screws are already in all the way.

  4. #4
    cmgww's Avatar
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    Quote Originally Posted by LT1GMC View Post
    His high speed screws are already in all the way.
    Yeah, what he said! LOL

  5. #5
    LT1 and I have been messaging a little about jetting. I have a groupk 1390 with lowell cut head like LT1. Lowell suggested 125/150, 2.0 and 80 g springs. Its a dog in the low and spins out to 7100 at 69.5mph. Its way too fat (along with myself lol) and I have all screws at .5 turns. Im going down to LT1s set-up of 115/135 at 30.5 psi pop off. Lowell sent me this (may be more applicable to your set-up with his porting):

    Are your restrictions drilled out and running a 95 main jet for a restrictor. Chokes & Accel. pump removed. Plus a primer. --- As per Oside Bill?

    Try 120 pilot ( I would not go lower than 120)
    145 main @ 1.5 turns You may need to go down to a 142.5
    Same 2.0 N&S w/ 80 gram

    Have you tried turning in the low speed to see if it helps?


    First I suggest you turn the (Low) adjuster screws in 1/8 –1/4 turn at a time and see if there is improvement. Remember when you go down with the pilot / low speed jet you must go up with the main / high speed to compensate for less fuel in low mid range – for final high speed tuning. I would stay with the 150 high and use adjuster screw. If you get in to less than 3/8 turn on LS then you need to go to next smaller pilot.
    You want to run as rich as it will perform – get on plane cleanly. When you mash the throttle you will get some fuel from high / main setting – this can have some affect on take off. Take your time – every engine and setup is different. Use the adjuster screws to tell which direction to go. If you are unsure always open 1/4 turn first and see if it improves rpm. If worse go in until it is runs clean.



  6. #6
    cmgww's Avatar
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    Finally got to tach it today...this morning. High 70 temps, decent humidity but not stifling yet.
    6950 RPMS. Yeah I would say its a little fat...and the prop is too steep. It's a 15/25, confirmed from LT1GMC. No wonder I'm not getting more speed! I pulled 76.1 MPH today, at THAT RPM. This thing probably has 3 MPH with the right prop and jetting down a bit. Brother's 1390 is a GroupK (a bit less aggressive setup than mine) and he is running a 14/23, same top speed and he beats me out of an idle start easily. I need less prop. 80 will be mine! (Commence evil laugh)
    Side note, got to ride LT1's FZR today...that thing is insane. Makes my 1390 look like a WaveJammer.

  7. #7
    Wish I wasn't in south cakalacky, I'd love to ride that FZR!

  8. #8
    Cmgww, out if curiosity, what jetting/pop off is your brother running on his groupk? I've still got some fine tuning to do but I'm running a 14/20 at 7050rpm on lt1's jetting, only getting 69.4mph

  9. #9

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    Roberd42, his brother is running the specs I gave you, that is my old boat. You may want to look at your scoop grate being all the way up in the hull and check the ride plate angle. Might be something there dragging you down, the GPR's are real sensitive to everything being perfect there. Check out some of the FAQ on ride plate angles and such.

  10. #10
    cmgww's Avatar
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    Yeah, lt1gmc knows more about that boat than I...
    i would say get a steeper prop, but you aren't over-revving. So look to the ride plate, grate, etc.

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