As Walrus said it would be best if we knew what type of SU carb you have. Perhaps they are even the Strombergs used on 60's vintage engines. In any event, if the carbs are HS6 (side float bowl) type SU's, then yank the choke control out all the way and visually check that the jet tubes have dropped. This can be seen as revealing a brass tube above the plastic jet assembly. If the jets don't drop with the control out, you must adjust the cables. SU's are terrible on a cold start without the jet drop (not a choke at all really). Both tubes should drop the same amount. When they do, the engine will fire up right away.
HIF and Strombergs use a fuel enrichment circuit, again not a choke in the usual sense, and rarely give trouble except to cause rich running when warm.

As Walrus it would be best if we knew what type of SU carb you have. Perhaps they are even the Strombergs used on 60's vintage engines. In any event, if the carbs are HS6 (side float bowl) type SU's, then yank the choke control out all the way and visually check that the jet tubes have dropped. This can be seen as revealing a brass tube above the plastic jet assembly. If the jets don't drop with the control out, you must adjust the cables. SU's are terrible on a cold start without the jet drop (not a choke at all really). Both tubes should drop the same amount. When they do, the engine will fire up right away.
HIF and Strombergs use a fuel enrichment circuit, again not a choke in the usual sense, and rarely give trouble except to cause rich running when warm.

It's most likely not your carbs but your spark(or lack of)
When I changed the carbs on my 68 it made little cold start improvment.
When I went with electronic ignition,I no longer needed a choke!
The spark on a stock 140 is very wimpy.Adding a HEI system is cheap and easy.
I'm useing a Bosch distributor GM ignition and a Accel coil.ACDelco plugs are
gapped at .050.(way better than the stock .028)My 140 has had this setup for
about 2 years and cant run any better.I've told other Volvo owners about this
setup and they dont seem to belive me or just can belive the FACT that the
spark can make that big of a differents.They are fools.



Ben.

Are your carbs HS6s (side bowl) or HIF6s (bottom bowl)?
If you unhook a fuel line before you crank is there pressure there?
Are your plugs clean and your ignition system good?
The only problem I have had at low temps was that sometimes it cranked
too slowly.
Better check to make sure that your chokes are working also - they are
necessary when it's cold. For easier driving during warmup make sure your
air intake flapper valve is working so you are pulling air from around the
exhaust rather than in front of the radiator.
I'd cover up about 2/3 of the radiator with cardboard for the duration of
the cold weather also. Your thermostat will regulate the temp but a radiator
full of very cold water may chill your engine before the thermostat can
shut it down, giving you poor temp control in very cold weather.

A field expedient that some would call cheating is to take a spray can of
starting fluid and giving a shot of it into the air cleaner box. (Don't
smoke while you do this.) It sometimes works wonders although you shouldn't
need it. It may also attack paint so be careful where you spray it.

One more question - are you using "winter" gasoline? The gasoline sold in
hot weather has a lower vapor pressure (= higher boiling point) so it doesn't
vaporize as well in cold weather. Winter gasoline has butane and other
higher vapor pressure components blended in so that it will vaporize when
the weather is cold. (In very hot weather it tends to evaporate faster.)
So if your gasoline is some you bought in July or August, a new tank of gas
might be helpful.

Also if you are running on the lean side that adds to the problems.
--
George Downs, The "original" Walrus3, Bartlesville, Oklahoma