E21 318 carb cold start issues

[golder6400]

I'm helping my father fix an issue on his 1980 e21 318 with a solex didta 32/32 carburetor.
When the engine is hot, it starts / runs / accelerates fine, idles at a constant 1k rpm.
When cold started, it takes anywhere from 3-6 tries to get the engine running (may have something to do with it having a mechanical fuel pump?), it idles pretty well, but when releasing the clutch to get going, it sometimes jerks, backfires and sometimes stalls, I can recall flooring the accelerator and nothing happening.
This problem is amplified A LOT when it rains. All these symptoms disappear when the engine is a operating temperature (usually 5-10 minutes after start). The engine is almost new (completely rebuilt in 2013 after engine failure), and the carb was professionally rebuilt in 2015. Is this behavior normal ? Could this be related to the choke ? I don't know much about how these carbs work, but I'm pretty sure all this shouldn't be happening.

[epmedia]

Absolutely could have to do with the choke. The choke is the 'warm up' circuit. Following the choke is the idle and mid throttle circuits. Assuming all mechanical is proper, a can of spray carb cleaner down the throat of a carb may reveal if the trouble is just routine maintenance or something else. (Blast half a can + down there, in the air vents and throttle areas to reveal if further t-shooting necessary)

Regarding 'amplified during rain' - may need to check for sparks in the dark. Or maybe inside the dist cap is moist, green, un natural appearance.

And welcome to the the e21 sub forum

[golder6400]

Thanks for tips, I'll go check out the car later