My gauge has a little rubber plug on it. When you break the seal on the plug it eases something in the gauge and you get an accurate reading. Your gauge might be fooling you.
Certainly take the top off and check your float level, so you can at least rule that out.
On the jetting, I would look over the specs/directions on "best lean idle" for that Weber 38 and see what it tells you. There is a certain amount of turns out on the idle screws and a range between when it idles rough on the lean end and then starts running rough on the fat end that you want to be that will indicate what idle jets you want. It sounds like you all ready know this but I would be remiss if I didn't mention it.
My kid is running a 38 and his likes to idle a bit higher than my 32/36 to remain happy. He likes a 1,250 rpm idle where I can run smooth at 900. That 38 is a badass carb and chucks a lot of fuel and air in there all at once. I wouldn't expect it to run like a smooth, progressive, economy carb.
You might also consider installing a vac guage and a good air fuel mixture gauge to take the guess work out of your tuning. They really help. When I was getting way into the weeds tuning I learned a ton after adding these gauges.
