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Need help with jet size

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Old 05-03-2007, 08:34 PM
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Default Need help with jet size

I am trying to get a carb tuned in on an hp500. The carb was freshened up and had #70 jets in the primary. The secondary numbers I cant make out. The motor is running very rich. Float level is correct, the air bleed vaves are free of debris, there is about .001 inch clearence on the primary accellerator pump rod. Are these jets too big? If so what should I start with. Thanks in advance for your input.

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Old 05-03-2007, 08:41 PM
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Is this thing a stock HP500? Is the intake the stock Dart? Those carbs usually had staggered jetting in them! Is it fat at idle or after its on plane? Have you leaned out the air fuel mixture screws? In is leaner and out is richer. You will be somewhere around 1 1/2 to 1 3/4 if its a stock carb from the all the way in on the air fuel screws. It may have a bad power valve, thats the reason for asking, if you run the air fuel screw in does the idle change and does it want to stall?

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Old 05-03-2007, 08:48 PM
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I screwed the air bleeds in all the way and it ran better, not good but better. If i let it idle long enough it will stall. The intake is a merlin. It is rich all the time. The power valve seems ok. There is no backfire through the carb on acceleration. It is a stock 500hp.

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Old 05-03-2007, 09:00 PM
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Was this carb recentlly rebuilt? Are you sure it has the right metering block gaskets? When you screw the air fuel in the motor should start to die out before you get all the way in. You still could have a bad power valve. 70 seems a little low on the primary side, should be in the 80's and the secondary will be just in the 90's to in the high 80's. Is this the stock carb that was originally on the motor?
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Old 05-03-2007, 09:43 PM
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Not the stock carb. The carb was just refreshened. The kit was a genuine holley. I gave them the part number off the choke horn, that doesent mean it is the right kit. The rear jets are HUGE. Way bigger than the front. Could this be my problem?
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Old 05-03-2007, 11:16 PM
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what number power valve is in your carb? maybe its staying open[wrong size for your application] which would make it run rich, also look on the secondary side where the base plate meets the throttle body you will see a set screw that adjusts the secondary linkage, if some one has this open to far it will move the secondary butterflies to far into the transfer slot making it run rich, i would also change the jets on the secondary side to a number you can read, maybe they are way to big
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Old 05-04-2007, 12:49 AM
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I just recently opened up a completely stock HP 500 800 cfm carb, and these were the jets in them.

Primaries 75 & 80
Secondaries 89 & 93
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Old 05-04-2007, 12:50 AM
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I'm pretty sure it's a 6.5 powervalve.
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Old 05-04-2007, 04:09 AM
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I'd double check the main body to throttle plate gasket. Sounds like you have a vacuum leak. The kit came with several of those gaskets. One is slightly larger than the other. Had the same problem last year that drove me nuts.
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Old 05-04-2007, 08:57 AM
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Thanks for the help guys. I will do some checking and post back.



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