New Motor, Jetting Recommendations
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New Motor, Jetting Recommendations

  1. #1
    Senior Member Bigblockbill's Avatar
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    Default New Motor, Jetting Recommendations

    Just put a new combination together and wondering where to start with my jetting.

    Its a 572, 12:1, running a Dominator 1250 carb with both power valves blocked off, burning a combination of 1/2 pump gas and Avgas. We are at 4500 ft so I will subtract a few jet sizes from sea level elevation. Did I leave anything out?

    We will have a LM-2 to do the fine tuning, just trying to figure out a starting point.

    Thanks
    Bill
    24' Eliminator Fundeck

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  3. #2
    Cantard 71hallett's Avatar
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    Quote Originally Posted by Bigblockbill View Post
    Just put a new combination together and wondering where to start with my jetting.

    Its a 572, 12:1, running a Dominator 1250 carb with both power valves blocked off, burning a combination of 1/2 pump gas and Avgas. We are at 4500 ft so I will subtract a few jet sizes from sea level elevation. Did I leave anything out?

    We will have a LM-2 to do the fine tuning, just trying to figure out a starting point.

    Thanks
    Bill
    Somewere around 90-92 I would think.
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    Quote Originally Posted by 71hallett View Post
    Somewere around 90-92 I would think.
    90-92 sure seems small. The carb was on a 588, 14:1, at 1300 feet elevation and had power valves in it and had 102 jets in it.

    Isn't the rule of thumb that if you take the power valves out you go up at least 4 jet sizes or more. Going up 4-8 comes to mind.

    Off course there are 16 less cubic inches and 2 points less compression, but dropping the jets down to 90-92 at 4500 feet of elevation seems like it would be very lean.

    I would think a baseline to start with might be something like the 102s plus 4 to 8 jets (let's say 4 for a starting point) for taking the power valves out, minus the extra elevation say 4 jet sizes and maybe minus another jet size for the smaller cubic inches and slightly lower compression. Does 98-102 sound like a good range?

    Am I missing something?

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    Senior Member stix818's Avatar
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    That just seems like a lot of jet. I would think 71 hallet is close!!
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  7. #5
    steelcomp was here
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    Find out what the carbs come with stock and jet up four from there.
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    Quote Originally Posted by steelcomp View Post
    Find out what the carbs come with stock and jet up four from there.

    Just got of the phone with Holley Tech Support, stock 1250 Dominators come with a 5.5 power valve and 100 jets in the front and rear squared off.

    So with that information, and removing the power valve, we should start around 104?

  9. #7
    Senior Member Bigblockbill's Avatar
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    Does taking the PV out add 4 jet sizes or more like 6-8?

    Plus this thing supposedly has been worked and flows more like 1400 or 1450... how does that change things?
    24' Eliminator Fundeck

  10. #8
    cfm
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    No answer to give you on the PV since this carb's been reworked. IE: possibility the PVCR has been modded.

    Call the carb company that built it and find out. If they don't know for some reason you can meausre the PVCR and compare it to the stock carb. BTW: Most Doms have a different PVCR than most 4150's, so that general rule for 'X jet' for plugged PV does not apply to everything.

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