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And speaking of the vacuum petcock, I think this has been mentioned but I'll say it too
The 3 barbs on the petcock are supposed to be connected as follows:
  • The large barb is for the fuel line
  • The small barb farthest from the body of the petcock is for the vacuum line
  • The small barb between the other 2 is for the drain/vent line.
Also, did you drain the carbs during all of this? Or for that matter, how long did it sit while you painted the tank? They won't start unless there is fuel in the float bowls and the carbs on these bikes have a tendency for the fuel in the float bowls to evaporate fast enough that if they are not used for a week or so the level can get low enough that there isn't enough for the engine to start. The problem is that the vacuum petcock doesn't let any fuel into the carbs unless the engine is turning fast enough to produce vacuum so you have to crank the starter long enough for the engine to supply enough vacuum to the petcock to open the valve for a long enough time for the float bowls to re-fill and it is pretty easy to run the battery down doing that.

There are a few options when you need to fill the carbs of a bike with a vacuum petcock:
1) Disconnect the fuel line from the petcock and add 90ml of fuel directly into the carbs (either with a funnel in the hose or by injecting it with a large feeding syringe).
2) Disconnect the vacuum line from the petcock and apply vacuum to the petcock's vacuum port (can be done with a vacuum pump or even by attaching a clean hose and sucking on it) for 10 seconds or so.
3) Disconnect the drain/vent hose from the petcock, connect a clean hose in its place and gently apply air pressure by blowing into it for 20 seconds or so.

BTW mariothtegee and KeenerDan: Welcome to the forum. Please add your location to your profile and your bike's model and model year to your signature so that you don't have to remember to tell us every time and we don't have to keep asking when you forget (see Forum Settings link in my signature).

And welcome to the world of antique vehicle ownership (they own us, not the other way around). Your bike is about 4 decades old and the Previous Owners may or may not have done the maintenance necessary to keep it safe & reliable so it is highly recommended to download the Factory Shop Manual for your model (available through the CX Wiki - link in my signature) and go through all of the service procedures, regardless of whether your bike has reached the specified mileage.
I also recommend looking on all rubber parts with suspicion because rubber does not age gracefully. Check the date codes on your tires and replace them if they are over 5 years old no matter how good they look & feel because old rubber simply cannot flow around the irregularities in the asphalt well enough to grip, especially if it is cool or wet. If your bike still has the original rubber brake line(s) (should be replaced every 2 or 3 fluid changes = 5 or 6 years) I recommend shopping for modern stainless braided ones (they last practically forever and double the life of the fluid).
 
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