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Old 08-06-2012, 10:45 AM
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Holley Carb Tune question

I have a 66 oldsmobile 425 that I am running at Holley dual feed carb on, (either a 650 or 750 not sure). I think I am getting close to getting the thing tuned in. The only little issue I am having is once and a while (not all the time) if I stop at a light or let of the gas for whatever reason when I return to acceleration it will stumble for just a second then clear up and run well. Any thoughs as to what may be the cause. I know I am close to getting the floats adjusted right (bottom of the sight plug). Dont know if the floats could cause this problem anyway. I have also adjusted the a/f mix screws as well so I know thay are close.. Could either of these two adjustmenst be causing this problme anyway? Any other thoughts?

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Old 08-06-2012, 11:00 AM
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Try setting your floats a touch lower. I've always set mine to have a little gas trickle out only when I lean on the fender.
Your little stumble could also be caused by a lack of timing during the transition. Where is your vacuum advance hooked to?
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Old 08-06-2012, 11:07 AM
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possibly the power valve maybe too big for your app. or may be damaged check your vacuum at idle and divide it in half the number you get should match the number on the power valve example 14hg/2=7hg would be a 7 0 power valve or your front jets may be a little too big or small drive the car at about 45 or 50 miles an hour were you can safely do this holding your speed turn off the ignition put it in neutral coast to the side of the road and pull a plug it should have a light gray tint too it black is too rich white is too lean
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Old 08-06-2012, 11:21 AM
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My vac-advance is attached to a vacume source coming from the front right cornor of the carb. Currently (and with the factory Q-jet) it has a "T" in the line and it splits off going to the automatic transmission mod. I may try taking the "T" off as I have plenty of vac sources on this carb. This car runs a lot of things from vac most important the headlights I am curious what pulling more vac will do to the operation of them. I could also hook it to the intake manifold as there is a couple sources for that thoughts? I will need to get a vacume gauge to check that to see what im getting, as far as what power valve is in it.
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Old 08-06-2012, 11:46 AM
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Likely you're getting a bog from the transition, this ca be fixed with a combination of adjusting the idle screw, idle restrictors, idle bleeds, and accelerator pump tuning. Id try adjusting the idle a hair richer and the accel pump in a hair sooner as those are the easiest fixes and will probably do an adequate job.
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Old 08-06-2012, 05:12 PM
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I don't really run the vacuum pods off of the dist. But when I have to I usually hook it to the metered vacuum port on the metering plate Or what holley calls the metered vacuum port "front metering plate right above the left air fuel set screw facing the carb from the front of the car" full vacuum on the pod usually brings the timing way out of the power curb the factory did this for emission control , however I was recently argued with that it was for gas mileage and my info was wrong so I really don't care about the arguement so take my advice or don't
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Old 08-06-2012, 05:57 PM
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What size are your squirters?? You can try going up a few sizes. when a holley has your simptoms thats usually the culprit. Not always, cause Iv'e had it not be the case. Just incase you dont know, cause squirters is not the technical term. look in your carb and pump the throtale with your hand and see where the fuel squirts out. look at the number stamped on the side of it and post what it is. Because if if you have to go up to a certian size you will have to upgrade your fuel pump diaphragm to a 50 cc. I doubt you'll have to do that though.
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