Selva 130 6hp on my Seawych?

Should I use my 6HP Selva 130 model on my Seawych?
It came with the boat, but has proved VERY difficult to start. Hence why I use my very reliable and trustworthy Seagull Silver Century. Both engines are the same age, but the Selva has had very little use all of its life. It’s in great condition.
Since changing the spark plug to an iridium type, and tweaking the carb, it seems much better. But do I trust it? I don’t know! Would you?
Unlike the seagull, this engine has reverse. Hence the reason to try it. But my confidence is not good. But it’s too good to scrap, so I just don’t know what to do with the blooming thing!
To Selva, or not to Selva? That is the question.