We have been straightening AMAL
carb flanges for some time now (see a 1994 letter from Mike Gaylord below).
In 1994 I received a letter Mike Gaylord who wanted me to publish it in Vintage Bike:
It is as follows:
5417 34th Ave SE
Lacey, WA 98503
John Healy, editor
P. O. Box 6676
Hollister (sic) MA
Dear John; Nov. 9, 1994
I cringe at the advice appearing recently in a popular
motorcycle magazine. Perhaps if you publish this letter
it will dispel the faulty practice.
The author prescribed the method of flattening a bowed
flange by, "Rubbing it on emery over a surface plate".
Its the same advice advanced by, "Experts", for years,
but now, stop and think. "That: method was employed by
Primitive Pete in the stone age, whose only concern was
to get the thing going well enough to reach the hunting
and gathering grounds.
Is "That" method appropriate for you today? No. Not if if
you are interested in getting the job done right.
Today we have better tools than old Pete's stone ax, to
deal with the job at hand. Having personally straightened
thousands of Amals, I feel qualified to discuss the cause
of bowed flanges, the proper cure, and the injurious
result of crude methods.
We note at our facilities, that the only flanges not
requiring straightening during reconditioning, are off low
miles Nortons and BSA triples. At least one assembler at
BSA had the "Touch", and understood that it is not necessary
to chin yourself on the mounting nuts.
Norton mounts their carbs straight to a manifold and the
flanges stay flatter than the flanges of carbs that are
mounted against insulator blocks, as is/was the practice of
most British makes.
The insulator block is of fiberous material that will crush
under excessive pressure. An unskilled mechanic will install
a carburetor with crushing pressure almost every time.
The crushing of the insulator allows the flange to bow.
As the flange changes shape, stress is created in the
casting, causing the walls of the mixing chamber to go
out of round. In severe cases, the slide used therein will
bind and stick... a very dangerous situation!
Flycutting or lapping the flange does not correct the
distortion in the mixing chamber, but does spoil the
casting by thinning and weakening the flange, while
allowing the distortion to remain.
Internal distortion is corrected and the flanges are
straightened with special fixtures. The process is the
first and most important step in our reconditioning
sequence, as it restored the integrity of the casting
and retains the original strength.
If you are dealing with a bent carburetor body, have
it straightened. Never lap or flycut a flange, as metal
removal methods do irreversible damage.
Also, an insulator block that has been crushed should
not be reused. the block may appear flat, but it will be
spongy instead of firm in the falnge area, and will no
longer afford a carburetor flange the necesary support
and a straight flange can easily be ruined by such an
Very truly yours