vinegar

[b_boy]

Acetic Acid is really a pretty potent acid, it's not sulfuric or nitric, but it will burn you skin off easily. I would personally avoid acetic acid its pretty corrosive over the long run.

If you do want to clean out the system there are other good solvents that are less likely to cause harm. Ammonia is one, as in Windex. Its available at any grocery on the bottom shelf in cleaning supplies. It's cheap and highly effective grease cutter and mineral solvent. It has the added benefit that the remainder evaporates. It does stink.

Another is Bicarbonate, baking soda is sodium bicarbonate, Na2HCO3. A 1% by mass solution will disolve many calcium deposits in your water lines and I would think have minimal effect on engine performance. Injection would increase the amount of CO2 in the cylinder when gasified. Running constantly would not be good for the build up of various sodium salts.