Starter solenoid kicks in when grounding carbs...

So my long term '79 Special project is 98% complete. I've been casing small issues like the starter staying engaged for a second or two after it starts up....

Anyways while I was messing with it I figured I'd check the cam chain tension. The engine is a fresh 700 with a bunch of good parts. During the process I touched the wrench from the adjuster to the bottom of the float bowl(master power switch was on). When this happened the starter solenoid kicks in. WTF!?!

The only thing I can think of the throttle cable is acting as a ground and back to the carbs? but they are isolated from the boots.... The bike is wired from scratch as I started with nothing. What the hell did I do?

Now that’s a head scratcher. I’ll be following this to see what the guru’s say. Scary thing is getting a spark near the fuel. I have starter “run on” too and haven’t figured out how to get rid of it. I’ve gotten used to it and it doesn’t bother me do much now. Lol.

That's bizarre.
If the throttle cable sheath has a metal bend (as opposed to plastic) where it enters the throttle housing I could picture it making a metal connection there, and in turn somehow connecting to the wiring of the starter button.
Might want to visit the wiring of the starter button.

I'm guessing the starter button is fuggled making contact all the time, or the blue/white starter wire is pinched somewhere, and handle bar ground wire isn't hooked up.

Fuggled or not the ground path from the start button is through the bars. If the bars have lost the proper ground then they may ground through the carbs. Do your carb bodies touch anything other than the rubber mouhts? If so that may be how.
On the early models the bars grounded through a wire from underneath the risers to a nut on the upper tree. This grounds through the neck bearing to the frame. On the later models they ran the ground wire from the left side switch housing to a harness ground. You might want to run a wire from somewhere on the bars down to a harness or frame ground.
You mentioned rewiring the bike. Did you swap the bars for black bars? Paint and powder coat blocks the ground path.
Leo

The handlebar switch is a new repop unit, nothing pinched. Bars are aftermarket... everything is powdercoated. The carbs are rubbed mounted via JBM boots. The starter button works so it's grounding through the bars as intended. I'll try adding a ground wire.

I'd be interested if others bikes have continuity between the carb throttle bracket and chassis ground.

Try grounding the RH handlebar switch with a jumper back to the engine. Will that spin the starter? Yes throttle cable, twist grip housing is the only ground path for the carbs. The gas tank has no ground path either.
When I got it, my 70 had short plug wires, they would pinch between gas tank and the head. In heavy rain using clutch, front brake would apply spark voltage to my gloved hands, exciting! I installed longer plug wires, changed routing a bit, problem solved, rode three hours of rain returning from the Ozarks rally, a miserable but not shocking experience.