Yamaha sticks with the inline 4 engine – In the long run, Yamaha MotoGP has its sights set on winning the championship using an inline engine type, thus they want to maintain the current position. They have high hopes that they will be able to increase the power output of the inline four-cylinder engine by the time the 2023 season comes over. In an interview that was published on the website Crash.net, Yamaha Motor Racing managing director Lin Jarvis was quoted as saying this.
We’ve decided to stick with the Inline four. With Suzuki stepping out we’re the only manufacturer to continue with it, but we have a lot of knowledge and expertise with the Inline four and in our opinion, it’s not the format of the engine that is the restriction
They have stated that each engine has different characteristics, and they see a wider space to explore that type of engine. Yamaha doesn’t seem to mind that Suzuki won’t be competing in the 2023 MotoGP season, so it seems that they have no problem developing an inline type of engine alone. Because Yamaha had worked with the engine for such a long time, it enabled them to achieve even faster in the direction they intended to go.

Fabio Quartararo seems happy with the new Yamaha prototype 2023 engine
On the other side, Yamaha’s rider Fabio Quartararo seems happy with the 2023 engine prototype at the post-San Marino Grand Prix test
I’m really happy, we work on the electronics this morning because the character of the engine is slightly different.
“Now it’s difficult to know something. I made a 1m31.3s with a tyre of 26 laps, at the end you can put a new tyre and you don’t even feel it.
“But really happy, for the first test with a prototype I’ve made a really good pace and it looks good. 298km/h was on the slipstream, but the average we did over the day was also good.
source: 1. https://www.motorcyclesports.net/ 2. https://www.motorsport.com/