Front wheel size and cornering stability

[R6_kid]

My 1985 CB650 currently has an 19in front and an 18in rear and the front end feel quite nervous when cornering, this isn't helped much by the fact that i am running MX bars which are probably 1-2inches wider than the standard bars, and also put my weight futher over the front end.

Would changing to an 18in front wheel make the bike feel more balanced and stable when cornering?

[Sully60]

I would say (assuming you change nothing else) no. A smaller diameter wheel would generally make it feel more nervous.
I would check that the forks are working properly and the front ride height is correct, while you're at it check every chassis pivot point, especially the steering head bearings.