The
Oldcorollas FAQ
An FAQ dealing with KE1x to KE7x Toyota Corollas
Supplement to http://groups.yahoo.com/groups/oldcorollas
All stock units are Aisan-manufactured dual-throat single-choke
downdraft-type carburettors.
All throat sizes are 27/27 mm. 3K and 4K venturi diameters are
21/24 mm for single carb, and 20/22 mm for twincarb motors (3K-B,
3K-D). Jet sizes are 0.99/1.75 mm for single
carbs, and 0.84/1.40 mm for twincarbs. Throttle is operated via
accelerator cable with the
progressive secondary throat operating on a mechanical linkage,
although there is a weighted vaccuum-style "flapper" butterfly in the
secondary throat as well. These carbs flow around 150CFM.
Some carbs have an
ignition-operated solenoid switch to prevent run-on (dieselling), I
suspect that this came in around 1975 (with the KE30), however some
later model cars have been released from the factory with no solenoid?
I have
found a paragraph in a Toyota workshop manual that suggests this is
part
of the -C motor emissions system.
These original carbs are quite poor, having very little mixture
adjustment, and it would seem they
have poor fuel atomization qualities too (whoever heard of a standard
carb running RICH on a worked 4K?). There's isn't really much you can
do as far as modification is concerned. An open-side design air filter,
or Ram-Flo, will help throttle response tremendously compared to the
stock snorkel-type filter housing. It has been suggested that jamming
the secondary throat "flapper" butterfly open (put a spring on the
weight arm or something) could help, but just seems to reduce throttle
response at low RPM and make the car more noisy up high, maybe with
some slight midrange improvement in power.
Therefore, one of the easiest mods for these cars is to change the
carby!
A Weber 32/36 DGV
is the most common aftermarket downdraft around.
Usually you'll need to jet down a carburettor like this, unless someone
has already done the work for you, or you have a fairly modified
engine. For a 3K/4K, start at around 130 mains, 170 air jets, 50 idle
and take it from there.
Basic tuning tips: If the car "stumbles" forward but revs eventually
climb, you're running too rich. If the car just cuts and dies, you're
running too lean.
Other carbs suitable for these motors include: Weber 32/26 DFV (aka
Holley
5200), Holley 180, Weber 32/34 DMTT, Dellorto DHLA40 or Weber DCOE40 in
single or twin configuration, Dellorto DHLA45 or Weber DCOE45 in single
configuration. One of the best carbs I think you can find for one of
these is a Weber 28/36 DCD from a Mk1 GT Ford Cortina. You probably
wouldn't want to go much bigger
than that. I also have a Nikki 28/32 off a Mazda of some kind that I'd
like to try out.
If your non-standard carb has a fuel return line, block it, or T it
back into the fuel line before the fuel pump. If you are looking for
somewhere to flow the
crankcase ventilation tubes, it is "suggested" you obtain a charcol
canister and flow the hoses into these to be emissions legal. You could
also put the
crankcase vents back into the air cleaner as per original, but I don't
think the carby is a very good place for engine oil. I suggest you make
yourself a catch can, or get a rocker cover breather.
If you end up with a carb that has a different stud pattern, making a
mounting plate and cutting gaskets isn't hard, so you
could theoretically fit any carb onto the manifold, as long as you
taper the throats (or expand the original manifold) to create smooth
flow. The adapter plate on my Weber is about 15mm thick.
Other sources of bolt-on carburettors (ie: same stud pattern) for these
cars include:
- Celica motors (18R, 2T, 3T) which are still Aisan carbs.
- Datsun L motors, apparently these Hitachi carbs are just as crap as
Aisans.
- Mazda Capella and other cars with Mazda piston motors (1300, 626,
etc). I have heard mixed reports of these Nikki carbs, some people say
they are the bee's knees, some people would rather bolt on a DGV. I
have managed to score one, one day I'll kit it and let you know.