I had a 1995 Nissan 200SX that I had to get rid of, lamentably, at 160,000mi. I’d been diligent in maintenance, the car had no rust, and compression remained at 95% of original.
The problem was that the car ran excessively rich the last 6mo of its life. Like -6 MPG and can’t pass smog. After troubleshooting likely causes, and stumping both my car friends and professional mechanics, I unloaded it after pouring over $700 into it in parts+labor.
Now I wonder if I couldn’t have retrofitted it with a carb. Would this be remotely feasible? It seems all the sensors no longer used could be fitted with resistors to send a permanent “A.O.K.” signal to the comptuer. (Although the State might not be happy: even though emissions would drop, the OBD-II baloney would be compromised).
Shame, I bet that car had another 100,000mi in it 
Anything is possible but doing this is going to cost you a lot more than 700 dollars; not counting the hours of “engineering around” it’s going to take.
You would need a specialty carb of some sort, build adapters, change the fuel pump, work around the electronic ignition, etc. The specialty carb would probably have to be a sidedraft of some sort (Weber, Dellorto, etc.) and you could figure on 4-500 dollars right there.
It’s doable, but it’s going to be godawfulexpensive if you don’t have the ability to figure all of this out on your own.
If the car was getting mileage that bad then all of these people checking it out were overlooking something very obvious; fuel regulator flat out gone, converter plugged up, distributor WAY out of time to the retarded side, EGR stuck open, ECM fault causing the injectors not to pulse, etc.
This should not have been that difficult a problem to solve.
Anything is possible. Don’t forget to install one of those summer-winter adjuster.
Nearly impossible but I think that vehicle had a recall on the fuel injectors
I don’t know about your car, I did convert a 914 from FI to multi-carbs. You would have to find the correct manifold for your car and do quite a bit of redesign. It cost me significantly more than $700, and that was 20 years ago. It’s easier to just go buy a good car that predates all the ODB/FI nonsense. I have a simple rule; I won’t buy anything new enough to have a CEL.
I’ve gone the other way…but NOT back. And unless you’re working on a Classic (IMHO the 200sx doesn’t qualify) then it’s NOT worth it.
There are TWO steps…One…getting it to just run properly…And Two…Passing emissions.
Have you thought about a wrecking yard engine? Throw a battery into it, put about 3 gallons of fresh gas into it, start it up. See how it runs. Especially if you can find a newer model engine that will slip right into your car. Good candidates: something murdered in the back or rear quarters. Then it’s a matter of figuring out the electronics. As for cost of changing out fuel metering/pump/filters, carburetors, etc. against cost of replacement engine, they both run ‘beaucoup’ bucks.
If you had a 5.0L Ford or something, I’d say go for it, piece of cake. Unfortunately I don’t know anything about the motor in that car, but on the Ford -and a lot of motors, actually- you could just bolt on a carb-style intake manifold, a standalone electronic distributor, and add a low-pressure electric fuel pump, and you were set to go.
"… even though emissions would drop "
No, they definitely would not. The only way they ever got carbs to get anything close to acceptable emissions levels was to put a large amount of equipment on them that reduced their performance and made them pretty unreliable. And there’s no way you would be able to make your own emissions carb system-- it took teams of automotive engineers to fine tune a solution for each individual car-- and nobody ever made a carbed '95 Nissan that met 1995 standards. Also, you have multi-point fuel injection and, if you look at the intake manifold(s), you’ll see that there’s no way you can adapt a standard carb onto there without extensive modifications that will make the $700 you spent look like chicken feed.
Now, in the early days of fuel injection they had single-point fuel injection, which used a single fuel injector in the place of a carburetor and had a similar mounting scheme. In areas where emissions aren’t an issue, some find it easier to replace the fuel injector/throttle body assembly with a carburetor. This makes more sense because, one, the single-point FI didn’t actually have that much of an advantage over a nice carb and, two, because it was a very easy swap and carb parts can be easier to find than 20+ year old FI parts.
You probably would do better going to a real Nissan specialist and actually fixing the problem.