Have you drilled the 2mm hole in the butterflies? Inserting fuse wire into the circuits is more likely to destroy your carb than anything else. The hole is drilled in the butterfly to allow it to close further in the single-carb setup, thus allowing the progression circuit to operate further up the rev-range, eliminating the flat spot. If you do this, then adjust your idle jet and mixture to suit, you are well on your way in the adventurous world of single IDF tuning!

mmm I have seen fuse wire used to decrease teh jet size, by putting it through the centre, is this what you mean ?
I would maybe try it as a trial but then gett the correct size jet made to remove it so it didn't fall out later.

I definitely wouldn't drill 2mm holes in the butterfly. The exact same effect can be gained by using the air by-pass screws. I find I can't open my air-bypass screws much before the idle gets to high even with the idle screws wound out and springs on the linkage.

Make sure everything is ultra clean. The whole "my webers fall out of tune" thing is actually "I have crap fuel filters so crud blocks my idle jets". Weber idle jets block real easy.

I have never heard the fuse wire trick either.

I would put in the 60's and then try opening the air-bypass screws to lean the mixture back out a little.