cb 34mm dual solex/brosol progression

[joel.truher]

Hi everybody,

I'm dialing in the dual 34mm solex pdsit carbs on a stock 1970 singleport, and it's working pretty well, except for the spot *just* off idle, throttle barely open, map around 60 kpa: this region consistently misfires. i can't tell if it's going super rich or super lean, it's just misfiring (so the wideband sees plenty of o2).

is it "normal" to see richness in the progressive circuit, and need a whole lot of advance? i'm running 155/50 on 28mm venturis, which is a bigger main jet than stock, but the stock idle jet. most of the rpm/map range is fine, a little on the rich side in some areas but basically fine -- it's just this off-idle stumble that i'm struggling with.

here's the spark map, if you're curious. looks pretty advanced to me, but i really don't know. i think it feels better to bump up the timing near that area (the little finger of green sticking into the blue part), but i'm wary of going too far in that direction.

Screenshot from 2018-07-26 19-54-33.png

oh also, the stock distributor on this car is vacuum-only using ported vacuum, so it has *full* advance (38 degrees!) in that same range (1200rpm, 65kpa), which seems insane. is that what i should do with my spark map? that would put the high-rpm low-map advance at 50!

any ideas?

[joel.truher]

ok, for the sake of anyone who finds this thread in the future, i bumped the idle jets up to 60 and that fixed the problem. now the off-idle stumbling is almost completely gone, and AFR mostly stays between 13.5 and 15.5. idle mixture screws are almost all the way in.