1.5 pierburg carb fuel economy

Running a 1.5 JB engine with a Pierburg carb and always had issues with economy. I swapped it from auto choke to manual choke to try and solve some economy issues, but still getting about 15mpg out of it on short trips.

Tried adjusting the idle bypass and co2 screw to get it balanced but I can't seem to lean it out anymore or it'll struggle at cold/ has issues running at speed.

So far I've got the co2 screw about two and a half turns out from full in. Idle bypass is about four turns out from full in, to allow the revs to stay high when electrics are on

Car revs at about 950 at idle when warm.

Followed lots of guides and I can't figure out how to get it past 15mpg.

Some issues I see:

When electrics are on (lights/fan) revs drop on the tacho.

When starting from hot, the engine won't fire unless I give the carb a bit of petrol.

Exhaust smells rich at the best of times, leaving a fuel smell on clothes - but turning down the co2 screw causes it to misfire.

The tacho Dan surge up briefly when at idle and warm. Jumps from 950 to 1100 briefly.

Anymore things I can try?

I've rebuilt the carb with new gaskets and needles/jets and it's still playing up. I'm this close to selling it and buying a Diesel MK1 for economy (or heaven forbid, a modern car)

how short are the short trips and are they in rush hr traffic etc?

Early-1800 said

how short are the short trips and are they in rush hr traffic etc?

Probably about ten/fifteen miles to the shops, bit of A road driving so up to 60 for a couple of miles and a few roundabouts, never say idle in traffic for any amount of time.

Volks42 said

Early-1800 said

how short are the short trips and are they in rush hr traffic etc?

Probably about ten/fifteen miles to the shops, bit of A road driving so up to 60 for a couple of miles and a few roundabouts, never say idle in traffic for any amount of time.

Well if you are measuring brim to brim fill ups / mileage and not guessing how far £20 get you does sound low. Short trips in winter in rush could see it being sub 20 and long criuse in summer getting nearer 40 so average 30 ish should be reasonable fig.

Is it Automatic, or Manual?  

My Manuals got Great mileage on short or long hauls as in 25-30 in-town for my 90 Gas, and 35 in-town for my Diesel when I sold it after 20 years new it got 45 in-town, but over 50-55 when on a trip.   My gasser got about 32-37 on the highway on trips All in MPG as I live across the big pond.

My Automatics would get 15-17 in-town with the a/c on and 19 usually with it off.  On the highway it did 24-27mpg.  

Which is why I asked, as my 67MG would get 55mpg on the highway, and about 25-30 in-town.

Manuals rock for MPG but Autos when you live in hilly cities, rock for no shifting at all.  

It's a manual, only four speeds though. No mod cons like air conditioning so really not sure what else is causing it to get such bad mileage, other than possible carb tuning issues.

The small passage ways in old carbs easily block and even compressed air, carb cleaner etc won't budge it.once dirt entered it was the devil's own job to purge the whole car. Yes dirt comes out the petrol pump/filters only do a 50% job.
Carb settings like float level, throttle gap etc All have to be checked adjusted methodically. With a gas analyser+Instructions Usually from factory manual (haynes I don't think so).
All this is time consuming (expensive to pay for).
To save all aggro waste of money/time a weber kit was fitted in an hour and decades of uneventful happy use followed. See bren /white cabrio / most mk1 meets.
Working at vw this wasn't allowed, so had to mess with the junk pierburg made /vw had contract with.
This kind of fault is extremely difficult to fix and diagnose standing by it, so warning is: impossible probably miles away being honest Geezer.
The bigger 1.5 1.6 etc engines were longer lasting(where's the 1.1 1.3 =gone) but only as good as the carb/if clean fuel getting to it.

High float level=rich
Low level =lean
Read spark plugs =colour. for those without use of exhaust analyser.
A weber 32/34 dmtl (twin choke) should give about 30mpg+ and not far off performance to a Gti. Two side Draught weber 40dcoe with small 28mm vents =gti performance /same poor mpg as now but drive well.
A lot better economy is possible depending on driver and where it's driving.
Ps don't know if useful but weber 34 ich manual choke is gathering dust here - ask….