Timing affects AFR's for sure. But in your case, I don't think it's a timing issue. However, checking timing is easy, so why not do this?
What came first into my mind are the injectors. They are known for going out of specs, which is feelable at light loads too. Opening pressure and squirting behaviour can be very different, which can cause symptoms similar to yours
Search for injector testing here on forum and check them.
On the other hand, depending on your engine specs, AFR's over 14 could be simply to lean for your particular engine. Maybe try a bit fater is worth a try
BTW, is the engine jumping too or does it run smooth in this area?
I am sure, others here had similar issues too and will help soon
