After dropping a new replacement carby on the A12 in my Sunny, I've got an annoying problem. When slowing down to a stop at lights or a junction, the engine stalls. It always starts up easily, but it's (very rude word of your choice) frustrating. I've replaced the unmarked main & secondary jets with a 96 primary & a 150 secondary, as in an A12 carby. Before this the car wouldn't drive properly on the main circuit as you could drive the car down the main jet. As soon as you screw the idle screw open, it takes the carby off the idle circuit, so I can't just turn up the idle. I've used a vaccum guage & got the best idle vaccum. I haven't changed the idle jet yet, as it's a different style to the one in the A12 carby. I haven't changed the air bleeds yet, or the idle airs, could this be the problem. At the moment I'm blipping the throttle to keep the engine running, not something you can do if you have to hit the brakes suddenly. It's not the brake booster, as it'll do it with no brakes too. Feel like I've wasted the money. Has anybody had experience with these carbies & know what could be the problem.

I wouldn't bet my life on it, but I've seen similar stuff happen on a few cars, and it ended up being the float height being incorrect, so it'd either be just on the verge of flooding at low rpm, or leaning out. I mention this in particular because one of the occasions was a friend's stanza (literally about 20 years ago) and I was chasing my tail because he was adamant it wasn't the carb. Because the carb had just been rebuilt (which is more or less the same as a new replacement carb). So I spent a fair bit of time checking everything else out, and lo and behold, after eliminating ignition and vac leaks etc, there it was - the float level was way too high. I dunno how it happened (it is possible it was set right but they snagged the float whilst re-assembling the carb top lid section and bent it I guess, but I suspect it was just an oversight - they fitted a new needle and seat and didn't re-set float height, and the new needle and seat was different enough that the float was barely closing the needle and seat by the time it hit the roof of the carb's fuel bowl area).

Anyway in that case it was too high. In other cases if it is too low (and it also depends on whether the fuel bowl is in front of the carb or behind it, i.e. as you stop fuel sloshes forward, which will uncover fuel circuits if the fuel bowl is at the front, or potentially flood them if it is at the rear. SO you get that effect to some extent if you brake hard enough, but if the float level is also incorrect, it's starting from a 'closer to stalling' fuel/float level, and tehn being exacerbated by inertia.

Like I said it isn't 100% certain, but it is a place I'd definitely investigate.

I'm buying you a beer John when I manage to get down that side of the country, you too Paul for no real reason.

John, I think it might be the idle jet itself being too big, but I haven't investigated just yet. I'm getting better at driving around it,instead of taking the car out of gear & coasting up to the lights, I leave it in a gear with the clutch out until I'm almost at a stop, then I blip the throttle with the side of my foot while braking. After 2 or 3 blips it'll idle perfectly. So I reckon the increase vaccum of a closed throttle is pulling too much fuel in & drowning it. Another hint is in a weber publication saying if the idle mixture screw is less than one turn out, the idle jet is too big, & the idle screw doesn't seem to affect the engine speed until 1/2 a turn from closed. I'm taking Saturday off, & I'll spend some time looking at all these things. I just hope the idle jet is the same sort as the A12 one, or I might have to resort to soldering up the hole & redrilling it smaller. Got some tiny wee drills that'll do the job, though they're a bugger to find if you drop them.

The question I'd have is how did a much larger idle jet get in there. I would have to imagine that even a carb setup for a stock a15 would still idle reasonably (perhaps not perfectly) on an a12 and vice versa. too high a float level can definitely cause the symptoms, and is (opinion) easier to see actually occurring accidentally rather than someone physically changing the idle circuit components.

John, I've changed everything over to the A12 carb, & it's still doing it (stalling, that is). I think the problem might be with the distributor, as it seems it might be stuffed. To get total advance, you have to set it to 15 degrees inital advance, & it advances very slowly. Seems it's graphed for a big cam & webers. I'm waiting for an electronic dizzy kit from Chris Lyons. I'm hoping it doesn't like the amount of advance & stalls. If this doesn't work, I'll just put up with it & get the A15 rebuilt as soon as possible. Thanks for the advice,
the float level was the first thing I checked & it's right in the middle of the dot.

I have had the same exact symptoms when i swapped a15 to a12 with standard carb. Every time i brake at approach to lights the engine stalls. I have to downshift to 2nd, sometimes 1st to keep the revs up or i blip the throttle or i use left foot to brake while out of gear and right foot on gas. Very annoying and potentially dangerous. I always suspected my brakebooster but now i reckon its the float level in the carb as suggested by jmac

It took a while to find the problem, but it was with the distributor all along. It seems it was regraphed for a race motor with lots of initial advance required & a restricted amount of total advance. Or it was worn out. I replaced it with what was sold on E-Bay as an L series brand new distributor, but is more likely to be from an E15. Swapped the gear & plate on like the electronic conversion, got a GT40RT transistorized coil, dropped it in at about 10 degrees & the car is driving properly again, not stalling, etc.It's been really bad to drive seeing as the clutch started slipping due to the problem & was replaced with one of those heavy duty ones in the pink box. No torque off idle plus a heavy clamping pressure made every standing start an 'adventure'. So now the 'quick' engine swap seems to be right, it's time to get the A15 repaired. I think a 70 degree cam, 77mm pistons & such could make enough power to make this clutch necessary. Thanks again to John Mac for his suggestions, but it seems all the swearing I did at the carby should have been directed to the other side of the rocker cover.