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Old 04-23-2013, 07:07 PM
eric32 eric32 is offline
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Advice tuning holley 600 vs idle circuit

Hello guys me again I need some basic advice here on tuning my holley 80457 600 vacuum secondary carb idle circuit. I know about basic carb tuning quite well but am by no means an expert like some of you guys on here when it comes to fine tuning a carb. first here is my setup

350 sbc
dart shp 180cc aluminum heads 72cc chamber
lunati voodoo hydraulic roller 270/276 219/227 @ 50 515-530 lift. 112 lsa
holley 600 vacuum secondary
weiand high rise dual plane
9 to 1 compression.
Turbo 350 2200 rpm stall 3.42 rear gears.

Ok here is my dilemma. I got the timing all set and with vacuum advance hooked up I have around 30 to 32 at idle and around 18 degrees initial timing and all in by 3000 rpm.

Motor runs excellent from 2000 rpm and up but in order to have proper transfer slot position on the primary's at .020 I try to crack open the secondary's about 3/4 to 1 turn past contact on the secondary speed screw but it will cause my idle to be to high and the primary idle won't go down enough but on the flip side of things if I leave the secondary's open too much like that its causing a lean condition and surging at low speed under 1800 rpm from the transition cirtuit and too high an idle and an off idle stumble and the pump shot has all been checked for proper clearance and gets a good shot of gas.

And if I set it back at half a turn then I can get idle to be good and takes off without the bad stumble and backfire from lean tip in and goes just fine but then I have the problem of the transfer slot being slightly more then .020 and say maybe around twice that amount but I still have good tuning of the idle mixture screws and they sit around 3/4 of a turn out.

I know the jetting is not bad as plugs are good and tan and no surging going down highway at 55 mph at 2600 rpm. So I am getting the feeling here but I could be wrong that the holley 600 is a little to lean on the idle circuit for this cam but I want to get this carb to work as getting something else is out of the question and I know a 750 is more power etc but this is something I want to drive and get decent fuel manners with better throttle response.

I do have a set of quick fuel billet aluminum metering blocks both primary and secondary and they have a feature of being able to change the idle feed restrictions from .028 ( which is stock size on current holley blocks) to .031 and would this help me with better idle tuning and needing less transfer slot if I swapped out the holley blocks for the quick fuel blocks which have more fine tuning features and are for this and the 3310 carb as replacement blocks with a more performance type fuel curve which I feel this carb can use. Any opinions? Thanks guys appreciate your help.
Eric
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