That's a relative term! ;-)
On the 70-72 cars, it's not really technically a choke, but a cold-start enrichment circuit. Why is it important to mention htis? Because a "choke" and "cold start enrichment circuit" or "starter circuit" in a carburettor function very differently!
A "Choke" will work if you have your foot on the gas, "starter circuits" will NOT!
The Z does not have acellerator pumps on the SU's, so the pumping of the gas to "set the choke" does absoutley nothing.
What you have to do is pull the lever on the console back to the rear, and crank the car with your foot off the gas. On early cars, pulling the lever cracks the throttle plates a bit, but more importantly moves the jet lower to allow more gas to be sucked in while starting. On the later cars, they actually use a "Choke Plate" at the front of the carbs to strangle the airflow through the carbs causing high vacuum in the carb body, sucking up more fuel.
Either way, you get much more fuel than you normally would, and that's what a cold engine needs to start easily on very cold mornings. After the car starts, you can ease the lever forward slightly, and keep easing it forward as it gets warmed up. If you have manifold water still connected, the time the "choke" needs to be on will be less, but either way, once started, ginger application of the throttle can get you moving and underway until fully warmed up.
I personally use the thing to get it started, and let it run on fast idle for a minute or so, and then get underway. Once going, I just push the lever full forwared, disabling the starter cirtcuit in the carb, as once you're going it's not needed.
If you step on the gas while cranking on hte early cars, you disable the starter circuit! Same if you butterfly the pedal trying to "pump gas" into the car when starting. Don't do that! Same thing goes for Webers, Dellorto's, and Mikuini Triples and their starter circuits, but they have accel pumps, so they are usually just a "pump pump, vroom" start sequence, as they are usually jetted way rich anyway!
Don't feel bad, I know guys who still pump the **** out of the pedal before cranking the engine over for the first time in the morning! You just gotta smirk and shake your head!
Tony, that is one of the best comments on using a choke on Z-Cars I have ever seen !!! ... it is a (sad) time when the rudimentary principles of car operation becomes a lost art...but this forum is THE place for anyone to ask and be given the answer...there are NO stupid questions...we Old-Timers (I'm 72) sometimes forget we too didn't know all the answers (we do now, of course!!!)...and as the proud owner of a 78 280 & an early 74 260 I am STILL trying to learn more about them...
Another note about the chokes. Mine is a 71 and the choke levers on the sides of the carbs after a couple of months usually about 6 bend out of shape and then I have to bend them back or else it wont run the idle up enough to keep it running after my car is started. Got to watch that those L shaped rods dont get bent out of shape. Just my little quicks with my little Z Mark
Mark, make sure your lever is adjusted properly so you can't pull the pieces past their full-travel position. This will cause them to bend the way you mentioned. Every car I've bought, the cables were adjusted waaay too short, allowing linkage bending if you jerk the lever all the way to the rear.
Anothe thing to check is that the bottom parts are free of junk and gunk to allow them to move freely, this includes using the PROPER fuel delivery tubing from the float bowl, as using regular fuel line will add stress that can also add to bending the linkages. Silicone fuel hoses or the original Nissan flexible tubing is the only stuff to use down there. Lube with lithium grtease or the like, after a thorough cleaning. And make sure they both bottom out at the same time! It's all in the details...