Here’s the latest reader question, along with my reply!
Jim asks: I caught your interesting article (here) about setting float level on a carburetor and that made me think about reverting my 1990 Chevy truck to a carburetor. Is this a doable thing and would you recommend doing it? Thanks for all your excellent Diaper coverage, by the way!
My reply: This conversion (reversion) is very easy if you are doing it to a vehicle – like yours – that has a throttle body injection (TBI) system. Most of these have a TBI injector that sits on top of a conventional intake manifold and they work very much like a carb – spraying atomized fuel into the intake, where it is drawn through the runners to the the intake ports/cylinders to be burned. The difference is that the fuel is injected under pressure whereas with the carb it is drawn by engine vacuum into the manifold.
You may be able to bolt a carb directly to your existing manifold; worst case, you replace your factory manifold with one designed for a carb, ideally the carb you plan to use (e.g., a spread bore manifold for a spread-bore carb).
Of course, you will also probably have to nix your computer – which controlled the injection as well as (probably) the ignition. A stand-alone/non-computerized distributor may be needed – but again, no big deal as these are generally drop-in replacements on GM vehicles of that era.
The main issue you’ll have to deal with – maybe – will be emissions inspection. If you have to deal with it. But you can avoid it by registering your vehicle as an antique – which in most states exempts a vehicle from emissions checks. And your ’90 vehicle qualifies as it’s 30 years old (and in most states, a vehicle qualifies for antique tags once it’s 25 years old or older).
The main advantage to doing this reversion is to never have to worry about electronics again – for the most part. The distributor still has some electronic parts, but provided you keep a spare module and so on handy – along with a rebuild kit for the carb – you’ll have everything necessary to keep that vehicle running for another 30 years.
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