Removing 1970 Buick APT screw

[ponchoguy]

Just got my new APT screw and secondary rods from you guys today. Awesomely fast shipping!!! Very happy, you have made a customer for life.
Anyways, I was trying to remove the old factory APT screw and not having any luck - Even with heat, soaking with penetrating  oil and a modified screwdriver.... Any tips to remove it without damaging the baseplate? If worse comes to worse, I have a 1968 Buick baseplate that has the same APT. Can you throw me a couple of tips to pull the old one in one piece? Drilling did not work, special screwdriver that fit tight didn't work either. I was able to screw it all the way in but I can't get it out.

Thanks,
Tom

[Cliff Ruggles]

I run into one on occassion that will not come out no matter what I do.  Most come out just fine, if you heat around it with a propane torque before you attempt to turn it.

They can be drilled out, with a hardened center punch to pierce thru the hardened surface of the screw and a good quality set of bits.....Cliff

[billy 2]

Recently I had an APT screw that would not come out and I tried heating it, having a screw driver that fit the slot tightly, worked at it till I broke the head of the screw off!  If your luck is the same as mine when trying to drill out a screw and save the threads, it won't work for you, either!  Fortunately, I have a good friend that is a tool and die maker.  I told him about the problem and he had me bring it to him.  He set it up in an end mill and in about 30 minutes had it out and saved the threads.  So, if you are in the same place I was with the base plate you might talk to someone who works in a machine shop who could probably save it for you.  Trying to get the bit to go straight down the center of the screw is absolutely impossible doing it with a hand held drill.  Just my 2-cent's worth; good luck!  billy2

[A. G. Olphart]

I had a 1705 carb with that problem. 
On my carb, the APT screw was between the idle screws. 
I ran the adjusting screw in as far in as it would go, then cleaned the exposed threads in the base plate with a 10-32 bottoming tap. 
Worked that time, although YMMV.  Same thread pitch?

AG

  . 

[ponchoguy]

I ended up destroying the one base by trying to mill the broken screw out and went a touch too far. But on the 2nd base I had, I used one of the top plate screws and screwed it in until it bottomed out on the screw. Then I soaked it with PB Blaster overnight then heated it with a torch (fun!). Kept working the screw back and forth, and it came out perfectly. Also make sure your screwdriver is a perfect fit for the screw, it's a thick slot, yet the screwdriver can't be wide or it drags on the sides.
Cliff's new screw looks like it will work perfect in the slot, I'm looking forward to getting that carb in service and trying out the old style APT.