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  1. #1
    Tony's Avatar
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    What size jets would you use??

    I finally got my piston wash the way I want it, rpm's look good, and I can hit 50-51 mph on gps. The only problem is that my HS screws are way out. They're MAG 2 1/2 CEN 2 1/2 PTO 3 1/4.

    Stock jets are 67.5 and 110. I assume one jet size is numerically 2.5 higher in value since they're listed 110,112.5,115,117.5...etc.

    I'm bored .50 over and running PRO series reeds. The cylinders are running 135-140 psi across the board and I plan on getting some aftermarker F/A in the near future. I would like to err on the large size...in other words...I want to have the jets large enough so that the screw setting are close to or even less than the stock settings of 1 to 1.5 turns out.

    What would you suggest?


  2. #2
    Moderator beerdart's Avatar
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    I would say go up 15 points to 125.

  3. #3
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Sounds like you should be 112.5 already. If you cut the side skirts off the 780 stock F/A cover, it'll allow for alot more air. Maybe you won't need the aftermarket F/A's. Jets will change after you mod yours or buy different F/A's. I'd pick up a few difeerent sizes from 112.5-117.5. It's not unusual to have different jet sizes for different cyls. Like your PTO maybe needs a 115 already. Just my thoughts.

  4. #4
    Tony's Avatar
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    Quote Originally Posted by beerdart View Post
    I would say go up 15 points to 125.
    Alright, I'll try that under one condition...why? Next time I'd like to be able to answer my own question. Only way to do that is to understand how you came to that conclusion.

    Is it the .50 over and/or reeds?, my current settings vs stock settings?, planned F/A upgrade, All the above, or is it just plain ole fashion hard earned experience?


    I assume you raise the pilot the same # of sizes as the main?

  5. #5
    Tony's Avatar
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    Quote Originally Posted by xlint89 View Post
    If you cut the side skirts off the 780 stock F/A cover, it'll allow for alot more air. Maybe you won't need the aftermarket F/A's...... I'd pick up a few difeerent sizes....It's not unusual to have different jet sizes for different
    Thanks xlint. You mentioning modifying the current F/A gave me an idea. I didn't want to cut the stock one in case I want or need it in the future. I'm going to make a top cover out of plexiglass. In theory I should be able to see down the carbs when running.

    I guess you're right, I'll buy a small assortment and hope I hit it the first time out. Might as well pick up a dozen or so carb gaskets as well......yep, she's "Nickle & Dime" alright.

  6. #6
    Moderator beerdart's Avatar
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    Quote Originally Posted by Tony View Post
    Alright, I'll try that under one condition...why? Next time I'd like to be able to answer my own question. Only way to do that is to understand how you came to that conclusion.

    Is it the .50 over and/or reeds?, my current settings vs stock settings?, planned F/A upgrade, All the above, or is it just plain ole fashion hard earned experience?


    I assume you raise the pilot the same # of sizes as the main?

    After talking to one of the gurus. He told me that one turn out on the SBN carbs is like 10 points up on jetting. So i figure go fat or go home. As for the lows that would depend on how the transition is between low and high.


  7. #7
    Tony's Avatar
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    Quote Originally Posted by beerdart View Post
    As for the lows that would depend on how the transition is between low and high.
    What rpm/throttle position range is the transition in?

    From a dead stop I have good WOT acceleration all the way up to top speed. I also have good throttle response at any throttle position. What I don't have is a 4200-4800 rpm range. There isn't really a dead spot or stumble and the throttle/linkage isn't binding. The engine just seems to skip over this rpm range.
    Last edited by Tony; 08-29-2007 at 06:17 PM.

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