Hi, I just lowered (flipped) my stem and now my handling is really stiff? Any ideas?

Any help would be massively appreciated

I assume you have a threadless headset if you were able to flip the stem. Have you adjusted the headset as per this tutorial? https://www.parktool.com/blog/repair-...service#adjust

Obviously skip the bit on removing and re-installing it...

Stiff??? well when you flip the stem the handling stops being erratic... now if you tighten the headset too much obviously will feel stiffer. If neither of what i said satisfy you then elaborate what you are saying because means I did not get what you are trying to say.

I like Airburts's answer better. Sounds like just a bit too much side-load on the headset bearings. Loosen stem bolts so stem turns, loosen top cap bolt a bit, test, and then tighten stem bolts. If fork rattles or you can twist the spacers, it's too loose. If steering is difficult, it's too tight. Remember that the top cap is for finding and setting the right tension, and the stem bolts are for holding it in place.

Another possibility is that you now have the stem all the way down against the headset's top bearing cover and it's draging. See if there is any clearance between the stem and the headset and, if not, put a thin spacer under the stem to raise it slightly.

This is a job to perform off the workstand.

Adjust it so you can't rock the fork in the bearings with the front brake on, and when you pick the bike up by the seat, the bars turn fairly easily when you tilt the bike to the side.

It's generally a finer line between too loose and too tight with threadless forks.

Firstly let me just say how grateful I am for all of your insight, as you can see this is my first post and your help is fantastic.

After some fiddling around I discovered that indeed my stem was pushing down on the bearing cover and thus causing stiff turning of the bars. All is now well. Again, thank you.