...

You will want to keep the original design intact. It is really nice because it does allow you to use (with the proper finesse) only the lower flipper without activating the upper (which does come in handy sometimes in multiball)

If the response is really lagging that bad, I would suggest adjusting the switch before removing it.

Not sure if there would be an issue with using one switch for both or not though. I would say do it, and report back. I am sure others have thought about it as well.

That cap is a spark arrestor. You've doubled the current flowing now through the single flipper switch and capacitor, whereas before, the current was halved through two contact points. Likely not a problem unless the contact amperage rating on the flipper switch is marginal. You'll probably end up with more pitting and shorten life of the contacts on the switch.

True, comparing apples to oranges as far as environment and duty cycle....However, I'm sure you understand that WMS wasn't in the habit of adding parts for no reason. These games were streamlined to save costs, and so an extra switch (added cost) was installed for some purpose. Maybe to give independent control as an earlier poster suggested. Maybe to decrease pitting across the single set of flipper points. Who knows, but in a home environment, probably a non-issue.

The only downside I see is the potential voltage dip / drop from two coils firing together Vs milliseconds apart. If you do not have any voltage drop issues I doubt it will harm anything.

When I had my HS I switched the series wound flipper coils over to the more modern parallel wound coils. These do not arc as much and the tungsten switch contacts do not get hammered from arcing.
With both coils firing together watch for increased contact pitting , if any.

For what it's worth, my Black Knight 2000 seems to operate like you want your High Speed to operate. I've always wondered why it seemed to be the only Williams machine with an upper flipper where the upper flipper didn't operate independently.

Swapping to modern parallel wound coils eliminate the arcing and your contacts will last a lot longer.

Just leave the damn thing alone.

I saw this post regarding the flipper and hoped someone here might be able to help my friend who just bought a minty HS. The only issue was that one flipper was extremely sluggish. The other side worked as designed. When he got the game home and fired it up neither flippers work. All fuses tested fine. Any known issues about this particular game and flippers? Any help would be greatly appreciated. I am hoping that symptom was seen by others with more experience.

Were the fuses tested out of the game, or still in circuit?

Check connectors for flippers to make sure they did not get loose from moving the game (these things happen!)

Check for voltage at the coils.

Check switches by flipper buttons, they may need to be cleaned.

You're actually trying to remove flipper staging!? I promise you will benefit your game alot more if you actually learn proper flipper staging techniques. This feature is present even on new machines like X Men and Tron. This isn't an 'oversight' or inconvenience, and frankly it's one of the easiest techniques to work on.

No machine I'm aware of fires coils simultaneously with one switch but they may exist - even games that don't let you stage flippers (early Stern or Bally) have the rotation of a flipper trigger the next coil in the line... kinda like an EOS switch. I would guess that energizing two coils on the same circuit at the same time will result in weaker flips, especially if a ball is present in front of both flippers.

You won't damage anything except maybe the cabinet switch, and of course the amount of flipper techniques you have access to in multiball