Jetronic is a very reliable injection system. That's why they are 40 years old and still work fine on many bikes and cars.
Maybe you'll find more sophisticated and complicated injection systems, but you won't improve many things with them. The only advantage (if it is one) would be to get rid of the flow meter at the intake.
Jetronic is very, very reliable. The only problem you could have due to aging is wear of the tracks into the air meter box. Spare parts are still available at Bosch...
Apart from this, all the problems come from faulty accessories (temp gauge for example) or bad maintenance (leaking fuel hoses, clogged fuel filter...).
But Jetronic, and more generally K engines hate to have to run with bullshit configuration around, like no enclosed airbox around the flow meter, shorten exhaust that ruin the resonance, or "creative" electrical harness with cheap (or not) crap chinese modules inserted into. These system need a stable, specific environment to work, the environment they were designed to work with.
So try new injection systems, they are available for years, like Megasquirt, Sybele, etc. Useless unless you first deeply modify your engine.
If you are really skilled in programmation of a fuel injection system and in engine tuning, you'll maybe be able to make it work as well as an OEM Jetronic...only if you first get rid of all the so-called custom gimmicks that prevent your engine to work really good.
Maybe you're not really pissed off with Jetronic. It could be Jetronic that is pissed of with you.
