Holley base plate swap between 4780 and 870

[68charger440]

68CHARGER440, can you provide a pic of the specific drilling location on the primary throttle blades? I have a similar situation with limited tuning range on the four idle-mixture screws with a new Proform 750 carb.
Thanks.

What have you done to try and tune yours.  I don't want to be an advocate of this unless you have tried absolutely every standard tuning  procedure first.  It is a very last resort that I chose to try that after many tedious hours of tuning, and I am still not sure that there is not some underlying vacuum leak somewhere that I have not been able to find.  The holes gave me the control of the mixture screws and now I can  try to tune it the rest of the way, but have not been able to get to the garage this week to continue that process.  Now that I can adjust it I am going to finally be able to get the idle low enough to check for a subtle vacuum leak that wasn't showing up at higher rpms.

[c00nhunterjoe]

68CHARGER440, can you provide a pic of the specific drilling location on the primary throttle blades? I have a similar situation with limited tuning range on the four idle-mixture screws with a new Proform 750 carb.
Thanks.

I will say that before you break out the drill, flip the carb upside down and look at the idle transfer slots. Yours will have one on the primary AND secondaries. The secondaries typicly come fully closed. Open the secondaries until the idle transfer slot looks like a perfect square. Then do the same to the primaries. Reinstall the carb and turn all 4 mixture screws 1 1/2 turns from full closed. Start the engine and observe the idle speed. My guess is it will be too fast unless you have a large engine or radical cam.
      If it is still too low, then you need to drill the blade or change air bleeds if applicable.
   If it is now idling too high you are in luck. Turn the primary down to lower the idle to where it needs to be then set your idle mixtures with a vaccum gauge and you are good to go.

[Nickrc3]

I will say that before you break out the drill, flip the carb upside down and look at the idle transfer slots. Yours will have one on the primary AND secondaries. The secondaries typicly come fully closed. Open the secondaries until the idle transfer slot looks like a perfect square. Then do the same to the primaries. Reinstall the carb and turn all 4 mixture screws 1 1/2 turns from full closed. Start the engine and observe the idle speed. My guess is it will be too fast unless you have a large engine or radical cam.
      If it is still too low, then you need to drill the blade or change air bleeds if applicable.

http://www.dodgecharger.com/forum/index.php/topic,109452.0.html

Appreciate the suggestions CoonhunterJoe. Unfortunately I've been through much all this. The cam is an outdated Purple Shaft 284/484 - told they are inherently difficult to tune. IAB's were increased from #70's to #76's. Drilling the primary throttle blades is now my next option.

[firefighter3931]

Nick, here is a pic of the drilled out throttle blades on a 4150 dbl pump type carb with 4 corner idle adjustment  


Ron

[c00nhunterjoe]

I will say that before you break out the drill, flip the carb upside down and look at the idle transfer slots. Yours will have one on the primary AND secondaries. The secondaries typicly come fully closed. Open the secondaries until the idle transfer slot looks like a perfect square. Then do the same to the primaries. Reinstall the carb and turn all 4 mixture screws 1 1/2 turns from full closed. Start the engine and observe the idle speed. My guess is it will be too fast unless you have a large engine or radical cam.
      If it is still too low, then you need to drill the blade or change air bleeds if applicable.

http://www.dodgecharger.com/forum/index.php/topic,109452.0.html

Appreciate the suggestions CoonhunterJoe. Unfortunately I've been through much all this. The cam is an outdated Purple Shaft 284/484 - told they are inherently difficult to tune. IAB's were increased from #70's to #76's. Drilling the primary throttle blades is now my next option.

You missed the point. I already read your topic. You continued to adjust the idle screw after you set the carb back on thus overexposing the transfer slots most likely. You have to set the blades first. If it wont idle and you have no leaks, then you need to drill, not take a screwdriver to it.