I haven't read all of the other posts, so please forgive me if this duplicates what others have already written.
Russia could have been a Central Power, if Austria-Hungary and Russia came to an agreement over the Balkans in the 1880s that led to the League of the Three Emperors continuing until 1914.
However, if the League of the Three Emperors has still been in existence the assassination of Franz Ferdinand would not trigger World War One. Russia would not back up the Serbia against the Austria; Germany would not back up Austria against Russia; and finally the German Government would not implement the Schlieffen Plan.
Germany would have needed another reason to invade France, and as no "Russian Steamroller" gave it more time to defeat France the German Army might have devised a war plan that didn't involve invading Belgium, and that might have prevented the British entering the war.
Assuming that the butterflies don't change the size and quality of the belligerents armed forces and economies it's going to be an overwhelming victory for the Central Powers by the end of 1918 (and probably much earlier) or at the very least there would be a compromise peace on favourable terms to them.
Germany will be able to concentrate its entire army on the Western Front. I think this would be enough for Germany to defeat France by the end of 1914. I know that if France had survived the first blows they would have been defeated in 1915 before substantial British Empire reinforcements arrived because the German Army would have been too strong. If by a miracle the French held out into 1916 the German Army would not have formed any new divisions after the end of 1915. Instead they use the manpower to keep its existing formations up to strength and increase industrial production. The British blockade is irrelevant because the Germans get the food and raw materials they need from Russia. With more factory workers and more raw materials the Germans could have built up a bigger air force and navy. In the case of the navy this would have included completing the battleships Sachsen and Württemberg, some of the Mackenzen class battle cruisers and more U-boats.
Austria-Hungary benefits even more than Germany. No Eastern Front (and the huge losses their army suffered there) meant they could concentrate on Serbia and Italy. A smaller war would have put less strain on their economy, which with more labour could produce more arms. Amongst other things they could have built 4 Erstaz Monarch class battleships.
Russia might avoid the 1917 revolutions or they would at least be delayed. Not having to fight Austria-Hungary and Germany releases an enormous amount of resources that would be used to attack the Ottoman Empire with overwhelming force. In common with Austria-Hungary and Germany the Russians would build up a smaller army than they did in the real world because they did not need one and they would also use the manpower released to expand their navy and air force. They would have to fight a holding action in the Far East against Japan if that nation honoured its treaty with the British.
In common with the real world the Italians would bide their time. However, they would declare war against the Entente Powers because they thought the Central Powers were going to win the war and because they had been promised Savoy, Nice, Corsica and Tunisia from France, Malta from Britain and part of the Ottoman Empire if the Central Powers won. In the real world the Italian Army grew from 24 infantry divisions to nearly 70, but in common with Austria, Germany and Russia it is likely that they would form fewer new army divisions and instead expand their air force and navy. For example they might be able to complete the 4 Francesco Caracciolo class battleships by the end of 1918.
It looks rather grim for Britain, France and the Ottoman Empire.
The British would still seize the battleships that were fitting out and IIRC the Ottoman Empire entered the war because Admiral Souchon took the Ottoman Fleet to bombard Sevastopol. It would have been better for the Ottomans (at least in the short term) if they had joined the Central Powers ITTL because they would have been on the winning side and they would have got Cyprus, Kuwait, Egypt and the Sudan back. However, ITTL Admiral Souchon is ordered to take his ships to Trieste to join forces with the Austrian-Navy and the Ottoman Empire decides to declare war on the Central Powers. Not having to fight the British means the Ottomans can concentrate their army on the Caucasian Front, but as the Russians will concentrate their army there too the Ottoman Empire is doomed.
For the British Empire not having to fight the Ottomans means no Dardanelles Campaign, the disasters in Iraq, no invasion of Palestine from Egypt and possibly no Salonika Front. This makes the forces employed available to other fronts. The obvious place to put them is the Western Front, where they would be needed to help the French fight the stronger German Army. However, they might be sent to the Caucasus Front to help the Ottoman Army, but the reinforced Russian Army is so strong that the presence of the British Empire troops make no difference.
The Austro-Hungarian and Italian Navies had a combined strength of 5 dreadnoughts in August 1914, plus the German Goeben, which rose to 10 plus the Goeben by the end of 1915. Assuming that there were no losses this total could have been increased to 18 dreadnoughts and one battlecruiser by the end of 1918 if having smaller armies enabled them to build more warships. This effectively cuts the Mediterranean in two for the Entente, which means their merchant shipping will have to go around the Cape of Good Hope, which reduces their sea transport capability without the Central Powers having to fire a shot.
The stronger naval threat from the Central Powers means that the British have to strengthen the Royal Navy and their merchant marine. However, to do this they will have to reduce the production of munitions for the British Army. This would not be a problem because by the end of 1915 the Germans would have defeated France and Belgium, the Austrians would have defeated Serbia and the Russians would have defeated the Ottoman Empire. They would have been in a worse strategic position than the ones they were in for most of the Napoleonic Wars or even 1940.
The only thing that I think could prevent a Central Powers victory would be for America to join the war earlier. Having the Russian Empire as a member of the Central Powers instead of the Entente makes this plausible because it makes the war, "A fight for democracy," 2½ years earlier. However, the combined economies of Austria-Hungary, Germany and Russia are so strong (the first two have the factories and Russia has the raw materials) that the Central Powers still have a good chance of winning a long war, especially if they have occupied France and Belgium before the Americans enter the war.