I think the bulk of the large road racing tanks were made for the 5 Flashes that were entered into the 1950 TT. Kelbin Hardin bought a Lighting that had one mounted on it and I remember that Glyn Johnson recognized it as a Flash tank and tried to hunt it down in the 1970's. Kelbin still has the tank.
After the TT some of the Flashes were loaned to racers like Phil Heath and John Surtees to use, but they had to be returned to the Factory. I think that the shot of Surtees with the large tank is a shot of him on one of these loaners and it is not the bike his Dad bought later.
One of the TT bikes was rebuilt and sent to Cimic for Edgard Soares, who was an exceptional rider. It was ordered with a large tank and it was painted black. This became known as the "Black Flash." It is not known which racers were donors for this bike although the frame and engine numbers are known. The bike did not survive as far as I know.
The big tanks certainly fit the big carb, but they fit the stock tank also. This is a shot of my Flash in 1953 at Daytona Beach.
The rider is Canadian Cliff Venier. Eddie Stidolph, who owned the bike worked for a Harley dealer and was not allowed to ride for himself. Those who have seen the big carb set-up will spot the 1-3/4" big port manifold, which is tiny compared to the 32mm manifold. The 1-7/16" carb is clip fit and the remote float is mounted to the F106/1. You can see a shiny band just under the bell mouth of the carb that is holding the float to the F106/1. So, the fitting of the big carb did not seem to be a problem in the stock tank, although the attached float bowl would not fit. The float bowl, if attached to the carb, has to be adjusted so high that it hits the tank. This is due to the steep angle of the carb.
I ran most of my races with a 52T rear sprocket. I used a 20T CS sprocket and I had a 1.89 primary ratio. I did, however, use 18" wheels. I could have gone to a 19T CS sprocket and run smaller tooth rears. I think the major problem with the Comets is that you have to stay away from any sprocket smaller than 45T. This does not give you a large selection of gears. Ideally, for all racing you would like to carry about 15 rear sprockets. My lowest rear is 42T and my highest is 58T. I use the former for land speed races and the latter at Miller motorsports where the 52T sprocket does not allow me to get out of 2nd gear.
I can run small rear sprockets because I went to an adapter rather than a brake. I use a stock off the shelf 1/4" Suzuki or Honda sprocket made out of 7075 aluminum. This makes it easy to have a large selection.
I gear to hit 100-103 mph on the straight of any track. The single does not have enough power to go faster on the straight, you run out of time. I hit that speed at 7000 rpm. The MK2 is usually losing power over 6000 rpm, so it is not much good up at high rpms. It will do it, just not happily. You need a cam that does 7-8000. It is fine if the power drops, but it can't drop fast like the Mk2. If two Comets have the same gearing and you run one Comet up to 6000 and another up to 7000 on the straight, the 7000 rpm bike will be going 15 mph faster than the 6000 rpm Comet. This is a tremendous advantage between bikes that are similar. If you are passed by someone going 15 MPH faster at the flag you think that guy has tremendous HP, but he may be geared more carefully and using all the rpm's he has.
I am curious about the TT Flashes being red lined at 9000 rpm's. I don't think Mk2's will do well up there. Also, at 7000 rpm the piston speed is 4133'/min. in my engine. The Nascar guys run 4800'/min to prevent the piston from self destructing. 9000 rpm would produce 5315'/min. I suspect that with the technology and oils available in 1950 this would have meant certain destruction.
I build the pipe so that the inside diameter will pass the cubic feet/sec somewhere between Bell's target of 250 and Denish's target of 280 mean port velocity at 6500. That would be a 1-3/4" pipe with .049" wall thickness. These are just starting targets.
Norman is correct. It was a large light bulb that went off when I saw how the Factory set up their racers for the best handling.
David