As I see it, the passage from the screw head through the body of the jet is the gas pickup. The four holes drilled through the little tower must be vacuum pickup, as I notice that they are larger on a larger number jet.

Now, I have a stock 88 with unbored screamin' eagle pipes, the harley K&N style filter and the idle plug was undrilled, making me expect no changes to the carb either, as it popped back and would stall at stoplights.

I drilled out the plug and adjusted to no avail: four turns out told me it was lean...ran best when fully hot.
Ordered a #46 jet as 45 should have been the stock one. It wasn't - it has a 48 in it and still running lean.

I figure this jet is bogus anyway and the 46 won't work, so I took a drill bit in my fingers, and camfered the outside of the 8 holes in the tower, then clamped a .039" sewing needle in my vise. With a bit of wiggling, I could force the jet down over the needle with my fingertips, boring out each of the 4 drillways just a little.
The bike seems to like it cold to partially warm, (rainy here; can't ride) so am I correct in assuming that I have increased the vacuum effect on the gas passage through the needle, and am now picking up a little more fuel?
I just wanted to try this before going for a #50 jet to put in it; mechanic thought it shouldn't need that and most posts call for a 46. No intake leak I can find, so that's not it.
I liked the richer sound of the idle; seemed more steady - giving credence to my theory of operation. 46 degrees tomorrow and I'll test it again if it's dry.
Oh, and does anybody have the chart of jet sizes? I mean the measures in thousandths, not the jet numbers only.

 

Keihin jet sizes are in 1/100ths of a millimeter. A 45 is 0.45mm or 0.0177", 48 is 0.48mm or 0.0189", etc.
If the stock 45 (48 was not stock) slow jet doesn't work with a stock 88, you've got a vacuum leak somewhere making it lean.

 

No....common recommendation is a 46 when you change pipes and AC. Leak test gives no difference that I can tell, but may get a new o-ring anyway, just to be sure. For now, I'm gonna ride it to the gym and see if my mod worked. Bike only has about 4600 miles on it now. Hog shop said with the Screamin' Eagles and K&N filter the 48 should be enough...and it almost is, but isn't perfect.
Also, I think I'd like to find some allens for the float bowl since the phillips won't last for many more removals.
Thanx for the jet numbers.

 

The difference between a 45 and a 46 is 0.00039", very little. The only difference I could tell on my last bike was that with the 46 I could run the idle mixture screw a little less than 1/2 turn leaner to get best idle. A lot of folks say the 46 works better, but the difference is so small it's almost inconsequential. Since you already have the 46 and 48, experiment away.
At any rate, 4 turns out on the idle mixture screw with a 48 indicates something is wrong.
The float bowl screws are metric, m4x16.

 

Vacuum pickup???????

 

All I can say about the vac tube is that it's hooked up. I took a 20 mile ride today after my workout and had absolutely NO trouble with it at all, no popping, no stalling and a little bit better sounding idle. I was going to adjust it when I got home and did play with it, but ended up putting the screw back at 3 turns where it was. Whatever boring the vacuum holes did worked like a charm.
Golly gee, I saved 3 bucks! I sure appreciate you guys chiming in and helping; time will tell if something else is amiss, but today's ride was perfect - the first ride with a totally tight bike.