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Thread: Carb Jetting / Power Valve

  1. #1
    EliminatorJet
    I'm running a holley 850dp on a mild hardin marine 454 +.030, and I am running too rich near WOT. I'm not sure what I need to jet down to, or if i just need to change out my power valve. Here's what I have in there right now -
    Main jets - 75, 81
    Power valve - 6.5 Hg
    Secondary jets - 93, 89
    I don't know what cam I have, but it is probably the stock hardin marine - thanks for any help

  2. #2
    sanger rat
    Let me get this right you are running 4 different size jets in one carb?

  3. #3
    Moneypitt
    In order to establish what to change you will need some more info. At the throtle position where you feel it's too rich, what are you pulling for vacuum? A temporarily installed vacuum gauge will tell you if your power valve is open, which it probably is, as WOT vacuum is probably under your 6.5 valve rating. IMO your jets are a little large unless you are really twisting the motor hard, (over 6500). You could plug off the power valve, you may not even need one with that huge carb, and see how the motor responds. But the only way to evaluate the PV is to know where the vacuum is at. You may experience a slight bog, or hesitation without the valve, but most boats will drive right through it........MP

  4. #4
    PLACECRAFT20
    My Holley 850dp came stock with 80 jets alll the way around. This was on a Hardin marine motor. I cant remember the power valve but I believe 5.5 or 6.5.

  5. #5
    Fiat48
    I'm running a holley 850dp on a mild hardin marine 454 +.030, and I am running too rich near WOT. I'm not sure what I need to jet down to, or if i just need to change out my power valve. Here's what I have in there right now -
    Main jets - 75, 81
    Power valve - 6.5 Hg
    Secondary jets - 93, 89
    I don't know what cam I have, but it is probably the stock hardin marine - thanks for any help
    Why in the world would this be jetted like that? 93 jet in an 850?

  6. #6
    EliminatorJet
    Yes, 4 different jets all the way around (I bought this carb used) When running near WOT it will run fine for a few seconds then start to cut out, sometimes completely stalling. I shot some quick start fluid in the scoop while it was cutting out and it had no effect on it. Fuel pressure is good, float levels are dialed in too.

  7. #7
    PLACECRAFT20
    Install those 80's all the way around. Should solve your problem and run good. Im like fiat, I cant believe it had that jet combination. I forgot to say mine has two power valves. If yours has one the in the front and the back is blocked off you will need to richen the rear a few sizes. Get the part number off of the chocke horn and look the carb up on Holleys web site to see what came stock in that carb.

  8. #8
    sanger rat
    Can you get me the numbers off the choke horn? I'll tell you what that carb came with stock.

  9. #9
    atomickitn
    hey elem jet, I have always ran worked holleys on big and small blocks leave the 6.5 p/v in put 72 jets for prime and 82 for secondary that will cure the low end hesitation and the black stuff and give plenty of crisp response on the top without runnin to lean good luck,be sure to do a plug check.

  10. #10
    GofastRacer
    Why staggered jets on an 850dp!..

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