Jet sizes

Tudortomnz

Tudortomnz

Well-known member
Looking through copies of the Canadian Service Bulletins for Model A, [June 1930] is illustrated jets for LHD cars only. These are 20 main;19 comp.;20 cap & 11 idle.
It then lists corresponding jets for RHD at 18 main;17 comp.;19 cap & 10 idle. Part numbers are 'AF' [RHD] & 'AC'/'AFC'[Canadian design RHD].
Any of you gentlemen have any ideas why the slight difference?
The jet sizes did vary over the production years within Nth America also, but I wonder why the 'foreign' RHD's were different.
 
The only thing I can think of is they are adjusting it for service in generally colder weather. A Canadian Model A is more likely to see below-freezing conditions for longer periods than a United States Model A, and is unlikely to ever be driven in the kinds of heat found in Southern US.

This matters because cold air is denser than warm air. It makes sense to adjust the jet size so that it provides the proper air/gas mixture for generally denser air. Also, the GAV can now be run at the "normal" amount of turns as specified in the owner's manual.
 
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So AFC and AF got the same, both differeing from A... that may blow my initial theory over the sightly muddled use of "AF" which covered in England both normal 200 ci RHD cars and the cars with the substantially smaller AF small bore motor.
I've got Canadian, British, and some Australian and NZ parts books to dig through to see if anything can be deduced from those...obviously most British cars were headed for cold weather, while many Canadian RHD cars were headed for the Antipodes, which must surely have better climates than home.
Now why the differentiation of AF and AFC in Canada?? Difference?
I don't think Canada produced the small engines at all...they were only needed for GB and Euro tax law, no sense in shipping them to Australia. AF would thus not likely refer to small engine, but only to normal 200 inch RHD cars...AF in the US would simply have designated a RHD vehicle, and the Canadian bulletins would only have needed to cover Canadian built vehicles...so what exactly is the distinction between the two flavors?
 
This is pure speculation, but perhaps something to think about. I know one of the distinguishing characteristics of Canadian Model A's is the use of Robertson screws, which were not used on US cars due to Robertson's refusal to licence their use in the US.

Is it possible the difference between AC/AFC cars and AF cars is that the AC/AFC cars contain parts that were only licensed for use in Canada and perhaps certain other British Empire nations? AF cars were possibly RHD cars to be exported/assembled in markets where none of those unique Canadian parts could be used, or maybe equipped with locally manufactured parts in the destination country.

As I said, total speculation so shoot me if I'm wrong.
 
The second set of jets you listed, like the #10 idle jet, are the jet sizes for the early double venturi carburetor. The other set you listed are for the single venturi carb.

Ron
 
Thanks guys for your replies.
A bit of confusion over 'AF & AFC' which were just part numbers [jets] for RHD cars & RHD parts made in Canada, not USA.
Canada did not manufacture small bore engines for export, but the European small engines did have a different carb & small jet sizes.
Dave/Franklin may have got it with air temps. Most RHD Canadian cars were exported to generally much milder climates [ India, Africa, Australia Malaya & New Zealand] than the coldest areas of Nth america. Hence the recommended smaller jet sizes? Could also be Ford was not expecting the cars to be driven 'as hard' as in Nth America.
 
Canada certainly made lots of specialized parts for export...in a later book, V8 years, there are several carburetors with jets sized for different altitudes, then one that is designated by designation: Nairobi!
Myt NZ and Australian catalogs show lots of early and odd stuff, including the early Canadian AA spoke wheels and a "9-speed" AA transmission! That one brought me upright in my chair! No description, but from the pictures I am pretty sure the "9-speed" was a 3-speed secondary trans, ratios unknown to me, after the regular '28-9 AA three speeds, and 3X3=9! Interesting that they had something utterly different from the USA planetary underdrive...this thing was a conventional sliding gear setup of some sort.
Hard to see the need for 3 under...maybe it had both OD and extra lows??
 

In my Oz A parts book some jets are listed with 3 prefixes:
A
AC and
AFC

It lists all the jet numbers Tom mentioned but does not say why.

Manuel in Oz
 
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