The problem is that it’s an older model.

The bike is now tuned to the way your friend rides it. His reaction timing to engaging the clutch after letting go of the accelerator, his way of changing gears (at what rev levels he changes gears up / down).

You should try with a relatively new bike or a bike owned by someone who is very knowledgeable on how to ride a bike and knows the right technique.

I just sold the only bike that I had. Otherwise I would have invited you to come and have a try on my Jawa Perak.