1st Generation Specific (1979-1985) 1979-1985 Discussion including performance modifications and technical support sections

Air mixture screw not working?

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Old 03-06-23 | 12:47 PM
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Evan Christian's Avatar
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Air mixture screw not working?

I'm having an issue tuning my RB Holley. I can hear noticable changes adjusting the fuel, but the air mixture does absolutely nothing and I'm having a bad lean condition driving. Anything over half throttle it bogs down like it's not getting enough fuel. I have to slowly get on the throttle to try and accelerate. I think these conditions are linked but I personally have no clue. Anyone know what's happening?
Old 03-07-23 | 11:37 AM
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Sounds to me like either s vaccine leak or need more fuel........
Old 03-09-23 | 11:48 PM
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It seems to rev hang alot as it is and I could check for vacuum leaks but not very many places it could be where it could be that bad.
Old 03-10-23 | 01:51 PM
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welcome to the board.

what pump are you running with your Holley?
Old 03-11-23 | 12:09 PM
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It has a smaller Holley inline fuel pump, I believe it's a 25 gph 1.5 - 4 psi fuel pump. It ran decent before the rebuild, before it started pouring the boosters. After the rebuild it stopped pouring out the boosters and just dripping from them at idle. I adjusted the float to stop the dripping (which I believe it still does after a hard stop) and turned the fuel mixture screw a quarter but still bogs anything over half throttle without having to slowly lean into it. I believe the Holley part number is 12-426
Old 03-12-23 | 03:37 AM
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i think you need a bigger/better pump.
Old 03-14-23 | 04:58 PM
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I'm eventually going to get a bigger pump, but as of right now I'm going back through my carb and making sure everything is clean and clear. My intake bolts weren't all that tight, one of them even being close to finger tight. I tightened them up and I'm going to put my carb back together and gonna check timing to make sure everything is good. One of these ought to fix lol, updates coming later
Old 03-23-23 | 09:18 AM
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The mixture screw only affects idle. Specifically, only until the transfer slots are uncovered by the throttle plates. After that the idle mixture screws have basically no effect.
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