I have an old Wisconsin model BKN engine (7hp), which I'd like to try to
start. It has the old pulley with the notch to wrap a rope and pull
start it. (not a built in recoil like on must lawn mowers).

The engine did not come with the the pull cord. I just googled the web,
and found several .PDF repair manuals to download, but none of them say
how to make such a cord. I imagine I could buy a premade cord from ebay
or some where else, or get one from a Wisconsin Engine dealer, but I
know I can easily make one. It's just a length of nylon rope, (like used
on any lawn mower), and a handle. The end that goes on the pulley has a
knot. I already have a handle from a junked mower.

The question is how long the rope should be, and is there a special way
to make the knot on the end, so it releases as soon as the engine
starts.

Do anyone of you have such an engine with the rope, who can post the
length and describe (or post a picture) of the knot? I can buy that rope
by bulk, for under a dollar at the local farm supply store.