Really enjoying the game! The bike controls feel great, it's a lot of fun to play, and overall it's very well made.
So far I've only managed to clear Stage 3 and reach Stage 4 twice. The time limit feels extremely tight to me, especially if you're trying to make any mistakes along the way.
One thing I think would help a lot is having a short tutorial or hint at the beginning explaining that players should pay close attention to the curve warning signs. Without knowing that, the game feels extremely difficult, and it took me quite a while to realize how important those signs are for anticipating corners.
From a design perspective, I personally think the stage-and-timer structure is a bit less engaging than something like Out Run, where branching routes add more variety and replay value. My ideal approach would be a championship-style progression similar to Lotus Esprit Turbo Challenge on the Amiga, or games like No Second Price and Pime Mover. I find that kind of progression more satisfying because you're constantly working toward achievements over time, rather than being heavily punished with a game over after a single bad run.
Of course, that's just my personal preference. Overall, I think you've done a fantastic job, and the handling is probably my favorite part of the game. Great work!
gameplay (spanish):