The Motor Cycle Magazine
AUGUST 8th, 1912.
Automatic Carburetors and Twin Engines.
Sir —I have recently fitted a Binks two-jet carburetter to my 6 h.p twin Rex, and noticing a letter in last week's issue on this subject, I should like to give you my experience. The carburetter fulfills all the conditions mentioned by "Socrates." flexibility of the engine is increased in a marked degree, and 1 now run through all traffic on a 3½- to 1 gear; previously I had to use the -low.
The engine picks up quickly and without jerk after slowing down. The velocity of the air past the small jet is high at slow speeds. and a small charge of good gas is taken into the cylinder consequently there is no misfiring. The machine runs from 25 to 30 m.p.h. on the flat on the small jet alone, and the large jet is only used on stiff hills.
My consumption ordinary touring speeds on average roads is about 70 m.p.g. I carefully cheeked my last run of sixty-five miles, and the consumption worked out at 73 m.p.g.
FRANK .Hall,.
Combined Chain and Belt Drives.
Sir— Ixion in an issue of The Motor Cycle recently claim to have done much to popularise the combined drive. Be this as it may, it has taken him six or seven years to come to the conclusion that the speed gear is a necessity on a touring machine. Even today he has got the "hang" of the full chain drive.
Personally, I favour the combined drive from the simple fact that it is a decided step towards the chain drive and its adoption, and its winning the Junior T. T. will do a great good in exploding some of the popular ' fallacies regarding the chain drive.
Looking into the advantages of the combined drive over the direct drive, we get with the former a short high speed chain drive to a counter-shaft, thus being enabled to use a larger "small " pulley for the drive. This belt drive in consequence becomes more durable, and less likely to belt slip—two very desirable points of advantage. We are assured by riders of this drive that, it, is perfectly satisfactory. For years motor cyclists have been taught the press that the belt drive is best: now the press is going out to teach the motor cyclist, that the combined drive is better than belt that by introducing the weakest half of the much abused chain drive we are getting a better drive. This I thoroughly uphold from my own experience of various forms of drive. In use the combined drive adds one hundred per cent. to the life of the belt; we have this on. good authority from many riders of this drive. It also reduces the worry from belt slip. This result is gained by the adoption of the weakest half of the chain drive the high speed front. chain This is a point I want motor cyclists to understand; hence its repetition. In fact, the chain is given the first and hardest, pa t of the driving stresses to transmit., whilst the belt is let off with a comparatively light part to do. Even then the much abused chain wears longer than the belt, and gives less trouble on the way. This being a fact I fail to see the object of the belt at all; why have the back chain of the chain drive as well? The back chain gives less trouble than the front chain and generally lasts longer about 12000 to 15000) miles.
Designers are aiming at a belt drive that does not slip and has long life. There have been great improvements in belts and pulleys, and now by the introduction of the chain to help them out these aims have nearly been accomplished but we still do get belt slip and belt adjustments to do on the road. Directly the makers do attain these perfections in their belt drives they will only have attained the points of superiority that the correctly designed chain pi as brought out nine or ten years ago by Messrs Phelon and Moore, has held out to them for all this time. What is there in the belt itself that makes it so beloved of the average motor cyclist? Want of experience with chain drive, I think.
For those who do not know what a correctly designed chain drive should be.. I may say that the important points in such a drive are that it should have an independently adjustable slip clutch in addition to the clutch or clutches necessary for a speed gear if fitted; that the chains should not be long enough between centres to allow excessive side swing, and that easy adjustment should be provided. The Enfield. and A.T.S. are chain drives which satisfy these conditions. There are many other chain do not have slip clutches fitted, and these latter are only too likely to make the chain drive harsh. It is not an absolute necessity to have the chains covered, but only an advantage, and if they are covered the covers should be absolutely oil and dust-tight, otherwise the chains are better left uncovered altogether.
The first cost has more to do with the popularity of belt drive than whether it is the best drive. P F Maw
Running on Paraffin.
Sir—I should like to give your readers the benefit of my experience of running on paraffin. The following experiments were conducted on a 3 h.p. Triumph, with a 1911 B. and B. carburetter and 32 jet. The first fuel tried was White Rose oil, flash point 105° F. The tank was emptied of petrol and filled with this oil, the top, the top of the float chamber was unscrewed and filled with petrol. and the paraffin tap turned on. The engine started up easily, and, after running about half a mile, I thought it would stop, but no it kept, going merrily on the paraffin, so I tried a few hills. I found that I obtained slightly less power and that the engine would not run so fast as it was on petrol, and the exhaust was slightly smoky. However I ran for two months on White Rose, cleaning the cylinder and piston every hundred miles. I also found that the engine would not restart on this paraffin unless the engine was very hot. During a short run the engine got very hot indeed and Special air-cooled oil had to be used and advantage had to be taken of cooling the engine on every down grade, but with all these precautions the engine played the blacksmith's tune on steep hills, which could not be rushed. To start from cold by filling the carburetter with petrol was a troublesome and dirty task, so I rigged up a petrol tank underneath the seat, communicating with the carburetter by means of a cock and a one-eighth inch copper tube. A one-eighth inch hole was drilled in the spraying chamber just above the choke tube, and the copper pipe was pushed through the hole until its end was vertically above the hole in the jet. To start the machine from cold, the petrol cock was turned on and adjusted until petrol dropped slowly from the bottom air funnel; the engine then started at a walking pace, and after running three quarters of a mile the paraffin could be turned on and the petrol off. If the paraffin was turned on before the engine was really hot thick clouds of smoke came from the exhaust.
My last experiment was conducted with Royal Daylight paraffin, flash point 81° F., specific gravity .797. and heating value 20,100 B.T.U. per lb.. price 8d. per gallon. With this 1 found that I could switch over from cold after covering 200 yards on petrol. The machine climbed . hills better, the exhaust was smokeless at all times, and there was no sign of knock on hills, while the engine ran about 96 miles per gallon, and it was as fast as on petrol.
VULCAN.
G S Hall (3½ hp. Scale- Jap) at the start of the Sheffield and Haliamshire Club