Long story short got a basket case 3 wheeler. Got it running BUT the pull start mount bolt holes are filled with silicone. Tried the make a bolt into a tap trick with very limited success. Most so full can't get to the threads yet. Got a long reach tap on order but won't be here for 3 days. Some of these holes are around 3" deep filled to the brim. Clown must of used a caulking gun.

Run a 3" deck screw in about 3/4 of the way, grab the screw head with vise grips and rip out the silicone plug (long shot, I know)

pressure washer

I've used a drill bit that's smaller than the hole with success. Wobble it around.

wait for the tap

compressed air and something to dig in with?

My take on it:

If they are fine threads the deck screw (or maybe lag bolt) and pull has a better chance of working than coarse threads.

Drill out as much silicone as possible without buggering the threads. Try needle nose pliers to rip out the remainder. If that doesn't work, wait for the tap. You need the bulk out for the tap to work anyway so nothing is lost by trying the other methods first.

I would use a drill bit. The bit should clear most of it. And then a pick. Do you have any left hand drill bits. They might screw it out while you drill it.

No left had bits though a good idea. 6 MM bolts is what they are.

A 3" long 6mm bolt? That's crazy.

Does MEK dissolve silicone?? It dissolves about everything else.

Work a straight pick down the side of the silicone all the way around it. Then just pick away at it. Deal with that a lot at work, seems like people abide by the if s little is good then the whole tube worth is better.

use alcohol in the process...{ not to drink kind} lol it seeps under the silicone

Try clamping a deck screw smaller than the hole in a pair of vise grips. Heat the screw up fairly hot and see if it will aid in pulling the silicone out of the holes. Your not gonna want that silicone in there when the tap gets there anyway.

never tried this....but.....how about using a ball inflator on your air compressor. Push the needle in and see if it won't blow out. Some type of liquid under pressure may be better though.