Sorry to read about the bad experiences you encountered with your Big Dog Blackjack ZT mower.
https://www.bigdogmowerco.com/mowers/blackjack
Yes your correct, it does sound as if you did get a "last hour on Friday work shift, hurried put together lemon" of a ZT mower. What were the chances right?
Anyway, it appears as though both Hustler and Big Dog ZT mowers are made by the same manufacturer.
https://www.lawnmowerforum.com/showthread.php/22283-Hustler-vs-Big-Dog
I purchased a Hustler Raptor Flip Up and like yourself, I really enjoy the Flip Up feature of it. Makes cleaning under the deck and changing blades a breeze. Other than that no other problems, so far it has been a good ZT for the past 3 years using it.
But again, like you, I also did experience a problem with the Fuel Gauge giving incorrect or false indications on fuel left in the gas tank.
After calling the manufacturer and explaining everything etc. I was instructed to take it to an authorized Hustler sales and service dealer and they would take care of the rest.
Well they did and it worked fine for some weeks (months) but then started acting up again. After inquiring as to what exactly was done to my ZT to fix the problem, to the Hustler service dealer who did the work, I was told the Gas Tank along with its internal Fuel Sending Unit and Fuel Gauge were replaced with new ones.
Called Hustler and explained that the same problem with the Fuel Gauge was happening after only a short time with the new replaced parts and wanted to know if this was an ongoing-continuous problem, specifically with the Fuel Gauge on this type of mower?
You see the Fuel Gauge is not the problem. You can replace just that and you will still encounter the same problem.
The "color" (clear white plastic or black plastic) of the Fuel Tank is not the problem. You can replace just that and it may work for a certain amount of time but then the problem will come back after awhile.
The main problem is with the Fuel Tanks internal Fuel Sending Unit, that was the main problem (at least on my ZT Raptor Flip Up).
Was told that they (Hustler) had become aware of this problem with the Fuel Tanks internal Fuel Sending Unit not functioning or stops functioning after a short time and that they had since had another, redesigned Fuel Sending Unit in the works.
Since that time, after having my mower sent back to the authorized sales and service dealer, I made sure that they replaced the Fuel Tank with the "new Fuel Tank" that had the new re-designed Fuel Sending Unit in it and well since then it has been working as it should without any problems.
https://www.lawnmowerforum.com/show...ip-Up-Fuel-Gauge?highlight=Hustler+fuel+gauge
Oh and by the way, I don't know about the Owners Manual for your Big Dog Blackjack Flip Up but the Owners Manual for my Hustler Raptor Flip Up says that before and after running/using your mower that you should check all bolts, screws, etc. for anything that is loose.
Anyway, that's my $0.02 of it all for whatever it's worth.
Good luck with your ZT and I hope everything turns out well for you and no more problems.