Found my drawings, all holes are 4.5mm off the centre line, first pair 4mm up, second pair are 8mm up. I centre drill to pilot and produce a little funnel, start at 0.8mm and try that, you can then open them up as required but open them up too far and you'll get runaway idle. There is also a cut out I machined at 30° just cutting into the front face of the slide but you could file that out with a ½ round file, easier to do on a mill and keep it centralised.
Here's a pic of a slide closed, this is an early iteration when I was trying flat bottom cut outs and different hole positions, but it gives you an idea.
Apologies for the pants picture quality, took this on my endoscope.
See how you get on and try the 3d printed slide (that's what inspired me) but your welcome to dm me if you really get stuck and I'll cast another batch. I think Jay's right tho, I think the air filter may also be causing you problems, I'm still running with all mesh screens.