Magnum 8 surge

My 32 year old Magnum 8 mounted on my 1986 Wheel Horse tractor is showing signs of wear. After surging only at idle the engine is now surging at full throttle. In addition it is for the first time hard to start, coughs and backfires when it does start and shuts down and will not restart once hot. I can start it again after cool down with the same experience again.
Is this likely a fixable condition or is it time to think about rrplacement?

A couple thing to check also.
 
Throttle shaft for wear as the Walbro WHL were bad to wear out the throttle shafts and pass through carburetor shaft holes leading to lean burn conditions.
 
Also when it dies check for spark immediately. Might be a failing magneto coil.