I wouldn't spend anything on that old Tec. You can get a brand new Harbor Freight Predetor for $99.00. I priced a carb rebuild & tune up kit for a Briggs 5hp that was on the one I bought & was looking @ about $65.00 just in parts. You can swap them back out if you decide to move on, parts are cheap, & plenty of hot rod stuff out there for them.
You can have them swapped in about 15 min with common hand tools. The only tricky part is hooking up the throttle, & even that's not bad.
BTW, just my opnion take it for what it's worth.
Those roll bars scare the hell out of me of these yard karts. I think they instill a false sense of security, they add weight (not much I know) up high raising the CG making it more likely to roll, & if it does roll, it's what the passenger is going to grab leading at best to broken fingers. I you decide to run it might want to educate your kids not to hold onto it. Plenty of 4X4 shops have grab handles that velcro onto jeep roll bars, you might be able to adapt something like that. Just make sure that bar dosen't trap a harm hand or leg.
Bob