Just fitted new inlet manifold and extractors , both 1 3/4" . Having trouble tuning the carbie. The car is running very rough, . Original system was 1" stock. I have "leaned" the fuel mixture hard up . Car will now only run with the choke fully out. any ideas? carbie is HS4.

Check that the carby jet is correctly fitted i.e. not jamming the needle and thus stopping dashpot from moving. Then, as you have leaned it right off and now need the choke out, you should richen it up a bit and see what that does.

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1970 MkII Cooper S
1971 Clubman GT (Replica)
71 Clubbie being worked on (1275 + lots of stuff)
Moke (1275) Awaiting restoration - Currently sheets of rust holding some mechanical bits together!

Sounds like your inlet manifold is not sealing correctly ie. sucking air making it run lean.

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"Investing my Super in a Cooper" &
"Re-living my Surfing Past in a Woody"

yep the asket was split right under the inlet manifold . New one fitted now I have four cylinders again... thanks dudes