My low and high A plays really sharp. I’ve tried turning the head joint towards me, and adjusting the embouchure but its still way out of whack. Should I try adjusting the cork? It seems like no matter what I try with the embouchure, I cannot get it close. All the other notes are spot on.
Is it an antique Rudall design?
You can put some wax or melt some shellac in the upper edge of the A tone hole to bring it in tune.
I guess I don’t know the answer to that. I don’t know the difference between a Pratten and a Rudall design. Mine does have large tone holes though.
Is it an old flute or made by a modern maker?
If it is an antique, some were tuned to 430htz, that make s the A and sometimes the B sharp and foot a flat. With the Rudall you need to push the slide in further and blow more into the embouchure, but it sounds like you tried that. You can get some cabinet makers wax at Rockler’s and even match the color to your flute, putting a small amout in the upper part of the L3 hole will do the trick for you.
It’s a modern flute by a good maker. Should I try out your idea?
Nothing ventured … Try a bit of tape or blue tack first, if you like. You’ll know soon enough.
As Jon says, though maybe a query to the maker might also be worthwhile. But fiddling with the stopper won’t (can’t) help with this issue - that isn’t what it is for/does.
Sometimes makers will copy the classics, keeping the classic tuning of the flute.
Poster putty as MTGuru says is easily reversible, you could use chewing gum for that matter…
I had a problem of my A being sharp and my B even sharper, a far better player tried my flute and it sounded in tune she told me I should tighten up my embouchure and now it’s a lot better.
That’s interesting JohnB. Recently being learning the flute after being a whistle player and piper for a fair many years and have a flute I bought new and one that a friend leant me. The first has a pretty sharp c, the nat & sharp, and the second flute is flat on the c. At the moment I have the sharp c taped but have been wondering if it’s my still pretty loose embouchure, though the c is out of tune no matter how I alter the airflow. Will persistence bring the note more in tune or could it be the instrument?
If the A is playing sharp… You have to put that in the upper edge of the B hole, don’t you? 
Er, no… the B hole is covered when you play A.
It is all semantics, that is why I later posted to fill the L3 hole. 
i play pretty sharp too on the B A and G, i’m pretty nervous about moving the stopper though, so i’m still trying to correct it by covering more of the embouchure hole on the top notes, it works to and extent for me, but its really troublesome though when there are fast octave jumps…
arrrrrrgggggggg!!!
I wanted to mean the G hole! I’ve had the same problem as Jon C…
in fact i’m going to revoice an old french flute, thibouville, and i’ll have to reduce some holes and enlarge others… very confusing, all this holes and notes… 
revoicing the keys seems to be easier, i don’t want to touch the holes, just adjusting the keys’ action putting more or less cork underneath seem to be… the key.
Aaaagh! Please, where do folk get this false idea that moving the stopper can help tuning of individual notes within an octave? IT CANNOT!
The stopper governs primarily the tuning between octaves - the “width” of the octave - push it in a little if the octave (D-d, G-g) is too wide (if middle d is in tune at A=440 and low D is flat and high d’ is sharp - assuming no “flat foot”), pull it back if it is too narrow…
(Note - of course changing the “width” of the octave has a minute but even effect right through the scale, but not sufficient to correct glaringly off individual notes when the others around them are OK.)
The other thing stopper position does is affect tone quality and facility of tone production in the extreme registers. Pull the stopper back and the low register ("hard D etc.) will be richer and a little easier to obtain, but the 3rd 8ve will be harder to get and harsher: push the stopper in and the low end will be weaker but the high end will be easier to reach and sweeter. As always, compromises! And if you pull the stopper back to enrich the low register, you may also end up with slightly “wide” octaves - another compromise/trade-off to make!
But DO NOT FIDDLE WITH YOUR STOPPER TO TRY TO CORRECT INDIVIDUAL NOTES - you can spend hours doing so and testing against a tuner if you like - it won’t - CAN’T - get you anywhere.
It is a common experience even on Bohm flute to blow the L hand notes of the 2nd 8ve sharp - this is absolutely an embouchure technique issue and happens to early stage players regardless of how well in tune their flute is built or may be played by another player. The tendency of Rudall and similar antique 8-key flutes (and of modern ones designed after them) to have a sharp A in the 1st 8ve is a separate issue entirely, though of course it doesn’t help with the 2nd 8ve tendency to blow sharp! The (reversible/adjustable, non harmful) adjustment of the A hole (closed by the 3rd or G finger!) with wax is the way to go, though as noted in this thread and elsewhere, once you get a good, appropriate embouchure for these flutes, the flat-foot D and the sharp A both tend to come more into line - again, an issue of technique and practice.
Easy enough if you teach yourself to remember that (all) HOLES are named for the note produced when they are the first open one as you move down tube (in the fundamental octave) - for the note they actually give by ending the sounding length of tube. So for the open holes, they are named one note higher than the name of the fingering when they are closed. xxo ooo is the A fingering - first open hole is L3 (plays G when covered) - so L3 is the A hole. Etc. Holes covered by closed standing keys obviously play the note named the same as their key - the one they give when the key is opened.
bit negative don’t ya think?
not like it’s yer time they’re spending 
Bogman - never had too much problem getting C in tune, you could try different fingerings with C nat. It seems that a lot of these flutes aren’t quite in tune and they have to be “blown” into tune.
A tip that I picked up is to play a scale slowly against a sustained drone note like G and concentrate on the sound/tone you’re making or to play along with a scale making the slight embouchure alterations to keep in tune - doing this regularly has helped me a lot, I used to play along blissfully unaware that I wasn’t in tune on some notes until I heard some recordings of what I was doing which was a shock.
@ bogman - yeah, as JohnB says, it depends… I think you need to tell us more re: your C naturals and the flutes - are you talking keyed flutes/notes here, or just keyless and cross-fingered, and if the latter, which fingering(s) are you using? On period flutes, keyed or otherwise, the open C# (ooo ooo) tends to be a trifle flat - a compromise to help the cross-fingered C nat - and on keyed flutes you were/are expected to vent the C nat key to bring it up to pitch. If a keyed C nat is flat, first you need to check the rise of the key and the state of the pad - if it doesn’t lift far enough or a saggy pad is belling down into the tone-hole, that will flatten the note. As for cross-fingered C naturals - we hack that one to death regularly - use the forum search for further info. Suffice it here to say that on very few flutes is oxx ooo the best available fingering for pitch or tone - don’t be surprised if it isn’t too good/accurate!.