The "whitish deposit" is corrosion. Yes, you should make an attempt to remove it. Perhaps someone with more training in chemistry than I will chime in here; but in essence, a carburetor is a classic example of a Galvanic cell (battery), composed of two (in this case more) dissimiliar metals in the presence of a liquid. I have forgotten the correct terms, but the issue has to do with the bonding capabilities of the metals. The corrosion is the result of electron flow, where particles from one metal (in this case the zinc) are transferred to the new substance (the whitish deposits). Electroplating is a simply a controlled version of this issue.
After the zinc alloy carburetor bodies were cast, they were dipped in a "chromate solution" which (unlike the "paint" currently being sold to hobbyists) placed a protective coating on the zinc alloy. Eventually, the protective coating will wear off, and corrosion will begin. If the protective coating is not reapplied, corrosion will get worse and eventually destroy the zinc alloy. How long does this take? I can't answer than one, but several years. Lots of factors contribute. The use of alcohol (gas tank treatment, or ethanol) seems to accelerate the process.
Knowing this, why don't all carburetor rebuilders use the dip and reapply the protective coating??? MONEY! The dip used to apply the protective coating is a mixture of Hydrochloric, sulfuric, and chromic acids. Chromic acid (the "active" ingredient) is a known carcinogen and is regulated. To purchase chromic acid, one must have a permit (which requires an approved disposal facility). It is much too costly for an individual (or even small companies such as mine). We send all of our chemical work out to metal laundry companies. Due to the added cost of the chromate and electroplating, most commercial rebuilders don't use it; as most customers are unwilling (either knowingly or unknowingly) to pay for it. Unfortunately, in todays economy, cost (how low can we sell it), not value or performance, drives many marketing decisions.
Jon.
