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  1. #1

    Talking carb tweaking any one?

    i got a 780 that i shaved the domes a hair to pick compression up a tad. compression on all 3 holes are 140 140 140 all even so how do i tune the carbs just leave them stock.. or do i have to re jet them any ideas


  2. #2
    BlueFishCrisis's Avatar
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    You will need to get some time in on the ski and keep an eye on your piston wash. Start with the stock needle settings, open and close as necessary until a good wash pattern appears. If you are opening your high speed needles past 2 to 2.5 turns, you will need to look at moving up to the next high speed jet size.....

  3. #3
    so set it up with stock and run what 2-3 tanks then putt the domes off snap a few photos and some one on here should be able to help me out?

    whats a good way to break one of these 780 in? i was told to be easy and double my oil since its premix?

  4. #4
    BlueFishCrisis's Avatar
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    Break in procedure. You will want to look at it before 2-3 tank fulls. You can set the needles a bit rich to be safe, but I wouldn't wait for 3 tankfuls before looking at it. Do a search on here for piston wash so you can get an idea of what to look for. Get a small light to look into the spark plug holes before popping the heads......

  5. #5
    LaveyT's Avatar
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    There is a Ton of good information out there to read, here is some....I would be tempted to put larger jets in from the get-go.
    http://www.groupk.com/tec-carbs98.htm


    High Speed Jet / High Speed Adjustment Screw - While the main jet does effect metering up to 100% throttle, it's primary feed range is the 60-90% range. It can easily happen that a high speed jet can be slightly too lean, yet safe 100% throttle operation can be had by putting the high speed screw to an over rich setting (over 2 turns out). The high risk of this situation is a swift piston seizure if the throttle is relaxed to 80% after a long full throttle pass. At 80% throttle, the high speed screw is not very effective, and it's piston-saving fuel supply is greatly diminished. With the engine still running within 90% of peak rpm, yet the fuel supply cut by much more than that, a piston seizure is not far away.

    One method the boat manufactures have used to avoid this risk, is to use a high speed jet so large that the high speed screws must be set at 0 turns out (completely closed that is). This arrangement also eliminates the risk of a customer setting his high-speed screws any leaner than stock. While it sounds a bit unusual, the idea of running closed high-speed adjustment screws has some very sound technical merits (besides the protection against accidental lean settings). Many technicians feel that doing all the high speed metering with the high-speed jet (alone) offers for much more accurate metering of fuel in multi-cylinder applications. While we tend to agree with that concept, making high speed fuel adjustments with the internal jet only is a major pain in the rear. We prefer to make a compromise between these concepts by using main jet sizes that allow for high speed adjustment settings of less than one turn out. We have found that this approach virtually eliminates the occurrence of 7/8 throttle seizures.

  6. #6
    LaveyT's Avatar
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    How much PSI did you pick up on your gage after milling the heads?

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