I have 2019 Fatboy 114 and feel the back end is a bit squirmy on curves. I checked the tire pressures after my 1000 mile maintenance and found them at 34F 35R. Manual calls for 36F 42R (240mm Michelin). Would going up help or going down?

 

Your pressure is way below recommendation. That can cause soft sidewalks. Go to the recommended, and see what happens,

 

Welcome to the forum.....error on the side of going up on tire pressure.....but inflate to the recommended.

 

Thank you.That was my feeling. Got confused when I saw some you tubers recommend lowering the pressure for performance cornering at tail of the dragon

 

We won't be doing the tail of the dragon like a sport bike. I run mine at the same pressure listed on the down tube sticker. Bike handles fine. No squish.

Also, we don't have the ground clearance or lean angle to spare if running them at a lower pressure.

 

I'll bet you didn't see any HD riders reducing air pressure to ride the Dragon. On the few occasions when I took my sport bike to track days I found the bike handled better with about 4 psi bled off. My definition of 'handled better' is that it gave me more confidence in the corners.
I've ridden 3 different Harleys on the somewhat over-rated Tail of the Dragon and kept my pressures at 36f/40r as always. For whatever reason, I've never found reducing tire pressure on my big twins to be helpful in any way.
I've never ridden a newer wide tire Fatboy like yours (congratulations by the way!) but have read about people calling the handling 'different' or 'heavy', so who knows for sure? But, as stated above, I would bet your handling will improve when you get your tire pressures back up on spec.And, with a couple thousand miles behind you I'll bet the handling feels very natural. Our brains seem to adjust to the bike over time.

 

Welcome from Philadelphia, enjoy the ride. I would go 36f 40r.

 

I run 18-inch tires and always have the tire pressure at the high end of max. 42 on the rear and 40 up front. I had some service on the bike yesterday, oil change and some clutch adjustments, Less than a mile of leaving I pulled into a gas station to double-check the tire pressure, as the bike did not feel right, sure enough, it was 45 on the rear. A little too much for my preference. Over time, you just get a feel for works with your riding style

 

Go with what the manual says. P.S., I have three bikes and each bike has different manufacturer tires (Michelin, Metzeler, Dunlop) and the pressure recommended from each manufacturer is different.