Pope Clement IV died in November 1268. There were at the time 20 cardinals but one was away on crusade and never came back. The other 19 met in the Palace in Viterbo but could not agree who should be the next pope.
The magistrates at Viterbo locked the cardinals in the palace, reduced their diet to bread and water, and removed the roof. It was joked that the removal of the roof might allow the Holy Ghost to get through to them.
Two cardinal died during the conclave. Eventually most were freed on the basis they agreed to delegate the choice of pope to a committee of six.
In September 1271, almost three years after the death of Clement, they finally settled on the future Gregory X. There was a further delay though, because after three years procrastination they ended up choosing someone who was unable to take up the post immediately. Gregory was away on crusade with Prince Edward of England, and was not even a priest when elected. It was not until March 1272 that he finally reached Rome and was crowned Pope.
This article describes the process in more detail.
It was the methods employed at this conclave that gave the Council of Lyons their ideas.
The first papal conclave after the Council of Lyons was in January 1276. Whether because of the new rules, or otherwise, Pope Innocent V was unanimously elected on the first ballot. He died after only five moths. The next conclave lasted 10 days. The restrictions were rigorously enforced by Charles of Anjou, King of Sicily, in his capacity as Senator of Rome. He confined the cardinals so strictly, and cut their rations so drastically, that many cardinals were prostrated by the heat of the Roman Summer. After 11 days they elected Adrian (or Hadrian) V. Ref
Hadrian, noting the intolerable way they were treated, immediately suspended Gregory's rules. He survived the conclave by less than six weeks, dying without ever being ordained a priest. Some doubted the legitimacy of Hadrian's suspension of the rules, in the circumstances. Nevertheless the cardinals refused to be conclaved for the next election, but perhaps fearing what might happen, they elected John XXI within a month. He completely revoked Gregory's rules. The following May the roof of his new study, in Viterbo, fell in on him, necessitating yet another election. Freed from the threat of confinement each cardinal had his own habitation in Viterbo. They met up regularly to vote and then went back freely to their individual abodes. This went on for six moths before the local magistrates decided to lock them all in the town hall, bringing about the rapid election of Nicholas III.
Nicholas reigned nearly three years during which he made his brother and two nephews cardinals. After the next election had produced no result after five months, the magistrates tried a new approach. They arrested Nicholas's nephews accusing them of impeding the election. This led, relatively quickly, to the election of Martin IV. Outraged by what had happened the people of Rome would not allow Martin to set foot in their city at any point in his four year reign. The next pope, Honorius IV was elected within a week of Martin's death, before some cardinals had even been notified of the death. Honorius reigned two years and one day, dying in April 1287.
The next election, 1287 to 1288 was the deadliest ever. Six cardinals, out of sixteen died including four in four weeks in late summer. The survivors fled Rome, except for one. When they returned in February they elected the one who had remained, who became Nicholas IV. His death in 1292 led to a two year election process from which many cardinals, not being conclaved, were frequently absent. After more than two years an octogenarian hermit claimed he had a message from God that the cardinals would be punished for any further delay. They soon voted him in as Celestine V. He was regarded by many as totally incompetent, but he did reintroduce the rules on conclaves, appoint twelve new cardinals, and resign, The conclave following his resignation, in which Celestine's appointees were a majority, elected Boniface VIII on the second day, which was Christmas Eve, 1294.
The next conclave, too, lasted only a day, but the one after, in 1304-1305 lasted 11 months. The cardinals however did not starve. As soon as they got together they voted that the conclave rules would not apply to them.
The last very long papal election was 1314 to 1316. It began in Carpentras, but amid scenes of violent disorder the cardinals dispersed: some to Avignon, some to Valence, and some to Orange. There was no quorum anywhere. Eventually the Count of Poitiers, who became Philip V of France, persuaded them to assemble in Lyons promising not to lock them up. After three more months they were locked up, however, and their diet restricted. After lasting forty days of this they finally agreed on Pope John XXII. Ref
The next few elections were conducted expeditiously and the rules were relaxed in 1351.
During the conclave of 1549 to 1550, restrictions were imposed allowing only one course meals, but nothing was specified as to how much each course might consist of. An agent wrote:
The cardinals are on the one-dish regimen. The dish consists of a couple of capons, a nice piece of veal, some salami, a nice soup and anything you want as long as it is boiled. That is in the morning. Then, in the evening, you can have anything you want as long as it is roasted. As well as some antipasti, a main course, some salad and a dessert. The more small-minded ones are complaining about the hardship. If things don't speed up we'll see how they react when it comes to bread and water.
It never did come to bread and water despite lasting over two months This election was also known as the porous conclave with numerous visitors coming and going including ambassadors and what today we might call paparazzi, so the cardinals might not have eaten it all themselves. Towards the end windows were blocked to reduce light and ventilation, and cardinals were ordered to bed at 10.30. which may have hastened the decision.Ref
One problem they didn't have was that faced by the cardinals in 1242. After a year of indecision the ten cardinals were confined in a room with a leaking flat roof. It wasn't just rain they had to worry about. Also, there were guards urinating on the roof. A decision followed within a fortnight.
Even as recently as 1978, conditions in the conclave were hardly conducive to a prolonged stay. Cubicles were erected in long corridors with ten cardinals assigned to each toilet. Cardinal Hume said the cots seemed to have come from a seminary for the very short. Cardinals awoke to hear other elderly cardinals shuffling seventy yards along the corridor only to groan on finding their assigned convenience occupied.
Cardinal Siri complained of the August heat saying cardinals were dying of asphyxiation because all the widows were blacked shut, although the reason was security rather than discomfort. He rebelled and ordered them opened. Colour returned to the faces of the moribund. In past centuries his protestations would have been ignored. Whether the conditions influenced the outcome or not, the conclaves of August and October 1978 lasted only 2 and 3 days respectively. Ref
John Paul II ordered the conversion of a Vatican hospital into a guest house for visiting clergy, and this was used for the conclaves of 2005 and 2013. Far from complaining of intolerable privations, Pope Francis found the accommodation so suitable to him that, after his election, he declined to move out. Eschewing the papal apartments, he has lived there ever since.