It is generally accepted that Vincent Black Lightning's
and Flash's were fitted with specially made clip fitting racing Amal's
of 32mm bore. As far as I can tell this is generally true, but if you
examine photographs of the earliest Bikes (i.e. of 1948-49, the year
my bike is built around), you can see that the more standard stub fitting
10TT9's are fitted.
Jacqueline Bickerstaff in her excellent
book 'Original Vincent Motorcycle' also mentions that early Grey Flashes
were built with 1 3/16" (30.16mm) flange fitting Amal's and it is
these that I believe were also fitted to the earliest Lightning's.
This is also backed up by that well-known book by Roy Harper, 'Vincent
H.R.D. Gallery', which shows catalogue photographs of both 1948 and '49
models fitted with what look to be stub fitting carburetors. However,
the text states them (and the Grey Flash) as being of 1 5/32" bore
(29.36mm). Actually, when I think about it I am not sure these 2 photographs
are good reference shots of a production Lightning, as I suspect both
photo's are actually touched up shots of that well known works bike 'Gunga
Flange Fitting Amal TT's were used on early
As you might expect, it was these
earlier carburetors that I decided to fit. Reasoning behind this was
as follows. First off, photographs of the '49 spec bikes showed stub
fitting could have been a possibility. Secondly, trying to find a pair
of original clip fitting carb bodies would prove almost impossible (I
have actually seen a couple of pairs advertised over the subsequent
years but, not having a large sum of available cash spare, have not
even enquired as to their price!). Finally, I was intending my bike
to have the original Lightning specification of heads, i.e. one front
and one rear, not two fronts. I believe that stub fitting would be correct
for this spec, and am almost sure that by the time Vincent's had switched
to two front heads, they had also switched to clip fitting carburetors.
Two Front Heads fitted by 1951 but still TT
Carbs, now with larger 302 floats
The only problem with this idea was that, as my section on cylinder
heads explains, I had managed to bore both inlet tracts out to the later
used bore of 32mm, meaning I would have to attempt to bore both carburetor
bodies out to the same diameter. As far as I am aware, original 10TT9
bodies were not designed to be taken out to this large a diameter and
I was worried that there might be problems. Incidentally, something
Phil Irving points out in his book 'Tuning for Speed', is that 1 3/16"
(T10TT9) and 32mm (T10TT) were the only size of TT carburetors that
had the same bore all the way through. All other (smaller) sizes were
only of the stamped size on the engine side of the throttle valve. Before
this point they were of a larger size, to allow for the space taken
by the needle. I assume it was not possible or necessary on the 2 larger
sizes to need this 'dual' size of bore.
Towards the end of the Black Lightning's era a small batch of 1 7/16"
carburettors were produced for Manx Nortons and Vincents. I believe
a set of these were used by Bob Burns when he set the ultimate motorcycle
speed record at 185mph in 1955. I am not sure if these were T10TT's
(T5TT's?) or GP's. I have never seen a factory photograph of a Black
Lightning that shows conclusively that GP's were fitted. I would be
interested if anybody knows.
Gunga Din with clip fitting GP1's
fitted. Were thesefitted to production bikes though?
Selecting the Carburetors
As it happens, racing carburetors are something I have always been 'turned
on' by, so I had a number of 10TT9's available of various sizes and
types. I had already picked out 2 bodies that were in generally good
condition, ready to bore. These were flange fitting versions and were
'handed', the front cylinder having the choke barrel on the left and
the rear cylinder having it on the right. As can be seen from the photograph,
the left handed carburetor also had paint on it, which I suspect might
be original, I used this as a pattern for a new batch of paint, of which
more later. Incidentally, a lot of the carbs have now gone or have been
used since the photo was taken!
Neither of the carburetors were 32mm (no surprise there!), so it would
be necessary for each to be bored to that diameter.
As for the floatchambers, for the rear carb I would use a direct fitting
vertical chamber (ie no downdraught offset) but for the front head I
would use a remotely mounted chamber. A similar arrangement can be seen
on the photograph of a large tanked Lightning in the Postwar section
of this site.
Boring the Carburetors to 32mm
The first step was to strip the carburetors and remove the brass Primary
Choke sleeve from the aluminium main choke. These protrude into the
bore and leaving them in would mean they would be damaged when I machined
the new bore on the lathe. They are threaded into the main choke and
only have a very small screwdriver slot (bored through the centre),
with which to remove them. Over the years, the alloy bodies tend to
corrode slightly and if this happens the brass choke is almost impossible
to remove. This was the case with one of the carburetors and it was
clear that trying to remove it would only damage it beyond repair, despite
making a special tool jig to help with this task.
This was a real pain as it meant I would not be able to bore out this
choke in one pass, instead I would have to make 2 passes, boring from
each end into the centre, leaving a section surrounding the brass choke
that would be at the original diameter.
My collection of racing carbs
- take your pick!
. . . I used these. Original paint can be seen
on left handed carburettor
This was pretty much how
it worked in practice. For the carburetor that I had removed the brass
primary choke it was slightly easier, first I pressed the aluminium
main choke back in place, in the carburetor body and secured it. Then
I very carefully mounted one end (the stub end) of the carburetor in
the 4 jaw chuck of my lathe. I spent the next 2 hours trying to ensure
that not only the end closest to the chuck ran true, but also the other
end of the bore (protruding some 3 inches out don't forget) was also
running true! Not only that, but I had to tighten the chuck hard enough
to hold the spinning carburetor whilst it was being bored, but not enough
to damage the carb!
I found that the easiest way to ensure the trueness of the end closest
to the chuck, was to make up special little tool, consisting of a wheel
spoke, sharpened at one end, with a fulcrum point half way along its
This could then be inserted into the carburetor bore, where touching
the innermost point it acted like a 'trembler', indicating the highspots.
Although a very laborious task, once set up the actual boring of the
carburetor was quite uneventful in comparison. Though not a trained
engineer (although my father was), I am well aware that setting up for
a job can often take far longer than performing the job itself!
Finished Bore at 32mm - Looks a big hole when
compared to normal TT carb!
The second carburetor was of course
more difficult. Although I followed the same procedure as for the first
carb, in this case I could only bore as far as the brass choke, then I
had to take the carb off and turn it round, repeating the procedure. I
then spent many hours very carefully opening up the remaining bore by
hand with Rifler files and small grinding tools, being extremely careful
not to catch the surrounding area - not a job I would ever want to take
Both complete, the finished
job looks quite neat. Certainly I have to say that the size of the hole
(32mm) looks enormous. I only hope they work ok, especially as the centre
alloy choke body is perilously thin at this bore. As a final task, I
have carefully re-stamped the air choke casting with the new size (32mm),
instead of the original imperial size.
I did not mention it in the previous section but I had decided to fit
the bellmouths before I started the boring process. By boring them in
situ, it would ensure they were absolutely true to the main body bore.
There are (as far as I am aware) 3 standard lengths of bellmouths, short,
medium and long. Although I had various longer lengths, which personally
I have always preferred, you can see in photographs that the early Lightning's
look to be fitted with short bellmouths. These are of approximately
15/8" in length. As I did not have a matching pair of these I ordered
a new set from Autocycle Engineering (call 01384 -253030).
On the right is the 'short' bellmouth, With
a 'long' version for comparison
Although early photographs show Lightning TT carburetors with standard
TT float chambers, in about 1949 the later Type 302 float chambers were
introduced. These are slightly larger than the earlier chambers and
have anti-frothing baffles fitted. They are easily identified by their
slightly larger bodies and the top covers are held by 2 hex bolts, rather
than the earlier versions screw-in top.
Although I am not sure if this type of chamber were used with the earlier
carb type, they were certainly used with the 32mm carburetors, which
were the bore mine are now at. For this reason I had been saving a pair
of these float chambers for many years, the rear one being a standard
(vertical fitting) chamber, while the front one was a remote mounted
version (see Post-War sectionfor an example of these fitted to Lightning's).
Although I had owned both chambers for many years it was only when
I stripped them for rebuilding that I noticed that the standard (non-remote)
chamber had a smaller hole than the normal TT main jet holder, and therefore
would not fit without some modification. This was not a problem however,
as it was not a big job to mount the chamber on my horizontal miller
and bore the hole out to the required size. I puzzled for sometime as
to why the hole was a different size to normal. It was only this year
at the Founders Day Rally that I found the reason why. I spotted a similar
chamber for sale and it was marked 'Triumph TR'. Of course, I then remembered
that early Triumph TR's were fitted with 302 floatchambers, what I had
not realised is that these must have been 'specials' with a smaller
hole to fit the standard carburetors (can't remember if these were Amal
276's or SU's though).
Top of Floatchamber showing 'Amal' lettering
Old and new style carb tops. Top retaining
spring can just be seen in top left of photo, which is required when
using later version
I wanted to bring the carburetors back as close to 'as new' condition
as possible. To do this I wanted to fit the original side choke mechanism
fitted to TT carbs, so often removed from bikes being raced today. To
be fair I have never bothered fitting them to my racing bikes either!.
The original adjusters that screw into the top of the choke casting
had a very distinctive knurl and are very often damaged. Luckily I had
two good examples. Some of the other choke parts were missing, but again
Autocycle engineering was able to help.
TT carburetors were fitted with two types of main body screw tops, again
I think they changed around 1949. The inner alloy throttle cable holder
having a second hole drilled and threaded, to hold a square headed screw
identifies the earlier types. The purpose of this screw was to lock
the ring and stop it unscrewing. The later type was fitted with a smaller
alloy centre, with only the throttle cable hole fitted. In conjunction
with this type, a distinctive pressed steel spring was used to stop
the knurled ring unscrewing. This spring was itself secured by the bellmouth
I decided to elect for the later type, as I think it looks a prettier
setup. I only had one full set of bits so again; had to purchase the
other set new.
I had enough fittings to build up all the remaining parts. Some of these
were slightly the worse for wear, so I spent some time carefully cleaning
the faces up before removing as much as the original plating as possible.
As I have my own nickel plating bath, I then re-plated all the parts
with dull nickel, including the original slides (which are now a very
nice smooth fit). Although very time consuming, I have to say I am very
satisfied with the results, not to mention the satisfaction of having
plated them myself.
Skimming the seating face of a floatchamber
nut in my Smart and Brown Model 'A' lathe
Finally, I went carefully round all the main castings, carefully removing
any blemishes, and (of course) ensuring all mating surfaces were absolutely
Many modern restorations of racing motorcycles are in my mind spoiled
because the carburetors are given a highly polished finish. Although
very pretty, to me does not look correct, as they did not come out of
the factory like this. I had one carburetor body in my spares that looked
to still have some of the original paint attached. This is an unusual
yellowly-green colour, which I had also seen before on other racing
carbs. I went to my local car paint specialist and had a 0.5 litre tin
of automotive paint made up to as close to this colour as possible.
It turned out to be a colour fitted to very early Volkswagen Beetles!
After masking and applying a 2-pack alloy etch primer to all the castings,
I then used my small Devilbiss MP gun to apply the silver topcoat.
I spoke to the owner of Autocycle Engineering about this paint. He too
said he knew it had been fitted originally (although he also told me
he had seen many different shades over the years). However, he was not
able to recommend a type of lacquer that would stop the paint being
removed by petrol. Because of this, he does not paint the items he makes
One of my other hobbies is flying Radio Control planes. Like on my racing
Norton, the glowplug engines fitted to these planes use methanol fuel,
often mixed with high percentages of Nitromethane (rocket fuel!!). To
protect the engine bay of these planes I use a specialist 2 pack lacquer
called Super Tufkote, which is totally fuelproof. I have now lacquered
the completed carbs with this lacquer, and although they are yet to
be tested I am quietly confident.
Although yet to fit the correct main jets, I have now finally assembled
the carbs, complete with new washers all round. I will admit I am rather
pleased with the results and am really looking forward to seeing them
finally fitted to the bike.
finished articles - On the left is the rear head carburetor and on the
right is the front head carburetor with remote floatchamber
I almost forgot, although I will not be able to verify the sizes are
correct for this bike until I test the bike on the track, below I have
listed the sizes I have used for the initial build (these are taken
from Phil Irving's Tuning for speed and Vincent service records):
Press on the following link to read about how the inlet stubs were