Having seen this post about engine starting, or the lack of it, and near burst me lungs pushing at times myself, I thought the following might amuze, if you can’t be bothered go to the end… This is item is of no help at all, not ment to be, but then wattaya expect?
The carburation of petrol is really a very simple matter. Petrol is a trade name for a highly volatile spirit or distillation of petroleum, and differs only in degree from benzene or benzole, being recognized by chemists as of the “Methane” series; but by whatever name you call it, you may be pretty sure you have the right thing if the specific gravity does not exceed 0.68. The density, or S.G of the spirit, is easily tested with a densimeter and as petrol of 0.68 S.G. vaporizes very quickly at all ordinary temperatures down to 59 degs. F., (which is the temperature at which the density of the petrol should read 0.68). The reading or the density varies 0.45 of a degree for every degree of temperature. Thus, in very cold weather the density would read heavier than on a warm day.
There is this peculiarity of petrol when vaporized in a surface carburettor or otherwise exposed to air, that the lighter and more volatile constituents of the spirit are used up first, so that the S.G. of the residue is constantly increasing. It will be found that any petrol remaining in a vessel, which is not absolutely air-tight, will, alter some twenty-four hours, read about 0.70, instead of 0.68. So for this reason it is well to fill the carburettor only sufficiently to accomplish the journey in hand the quantity required being soon found by experience, for when the S.G. drops to 0.70 it will be with difficulty that the motor can be made to start, and this only in warm weather, or by previously heating the petrol tank. Old petrol will not mix with new—i.e. if the density is found too great, the addition of fresh petrol does not remedy matters, the engine simply uses up the fresh petrol, which floats on the top, and then stops. The vapor from the petrol is in itself not explosive, it must be mixed with a certain proportion of air. The exact proportion varying with the temperature of the atmosphere, but a mean quantity would be about 8 of air to l of vapour, the training of the ear to the sound of the explosions in the engine being the surest guide as to when the mixture is correct. With fresh petrol, which is very volatile, a much larger proportion of air will give effective explosions, but as the more volatile spirit is used up and the S.G. increases and at the same time the air space in the carburettor is increased, it becomes necessary to alter the adjustment valve and admit less air to the mixing chamber.
Why should this be of some interest to all “puffers and panters”? Because there is nothing new under the sun, this little gem was extracted from a series of articles about home building a motorcycle. And I do mean building, engine and frame, all of it! So you have joined a long and noble list! Why am I sniggering? Because my pile of bits is a long way from the starting stage, but maybe not so far from the kicking…
Have a go at guessing the date this was published. I’ll make a nice cherry & walnut cake as a prize for the closest guess.
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