Can you confirmed there is no debris that is holding the float open? There are two in line filters within the banjo fittings on the float chamber. Mine were full of crud, kept causing overflows on the rear carb. I would check that. The pump you have seems to have an OK range of PSI for SUs.

2000 idle is a lot, shoot for 800-900. You modified cam might want to make it go a bit higher.

get your floats adjusted correctly. One you have the floats set then you can use the guide, otherwise the guide won’t work!

I don't think so. When I manually move the float up while blowing on the fuel tube with my mouth, I can feel the valve close.

I cleaned out the banjo and put new fuel filters in recently.

The modified cam might make it want to idle higher, but not 1000RPM higher (I'd hope).

"get your floats adjusted correctly" - any recommendations vs what I'm already doing?

Okay, so i figured out why the sync tool was shooting fuel: the carb tuning guide says to plug all vacuum lines which were attached to the air box. I removed the plugs which i had put on the carb fuel bowl vents and it doesn't shoot fuel anymore.

The comment about getting the float adjust correctly was in comment to the sync tool showing  too much fuel. Now that the tool can be used the level can be confirmed.

What needles are being used in the carb? SM?

No idea which needles. Would I need to take it apart to check?

If they're from ztherapy there most likely SMs unless you specified different.

Post #11 has some info. 

The fat end has a stamp number if I remember right. So you'd have to pull them to see.

https://www.classiczcars.com/forums/topic/59153-modified-su-carb-needles-for-l28/#comment-537325

I'm not sure but I assume they're original to the carburetors. 

https://youtu.be/5KwKMwHtFMI

I'm going so nuts with this thing. I tried spraying carb cleaner all around the intake area again and it didn't seem to make a difference in RPM, but there has to be an intake leak somewhere, right? The throttle is all the way closed.

At this point I'm thinking it has to be something to do with the cam in there. It definitely seems like the previous owner put some sort of performance cam in there, but I have not idea what kind. In the video you can see the rear 3 exhaust headers getting red hot (timing, combustion in exhaust?).

I tried moving the distributor in both directions (retarded, advanced), but it didn't seem to make much difference. At the end you can see me jump from a huge bang. I assume it was fuel igniting in the exhaust.

At this point I'm so frustrated with this thing I'm considering just replacing the cam with a new one from MSA, or taking it into a shop so I can get some professional help..

 I can't imagine an intake leak large enough to idle an engine at 4,000 rpms. When you say the throttle is all the way closed, are you referring to the throttle pedal or the carb butterflies? I think your butterflies are partially open which would indicate something is wrong in the linkage. Mine did the same thing one time when I forgot to hook up the heat shield springs.

The butterfly valve is closed. The throttle return springs are on. When I push on the throttle linkage, it'll rev even higher.

Are the pistons up or down when it's running? If they're up it would indicate the butterflies are open. If they stay down it would indicate an intake leak.

It's hard to tell from the video, but I believe they are raised a bit. I'll get a better video or some pictures tomorrow. Last time I had the carbs apart It seemed like the butterflies were closing fine, but maybe I'll take them apart again to check. What should they look like when 'closed'? Should the butterfly be straight up-and-down, 90° to the intake? I remember them being at a slight angle to the intake.