Saving Old Seagulls

Help!
My always reliable 40+, ( Ive had it for 5 years) and it always started 1st or 2nd pull.
Last week I removed the propellor and tried to run it in the 'test-tank'.
It has now decided to only run with the choke fully closed. Starts easy, idles or runs at any revs, but open the choke and it just dies!
I've adjusted the needle and even swapped needles (10:1 and 25:1), stripped the carby to the tap on the tank and cleaned it, I've swapped the carby with one from another 40+. Checked and reset the points. Changed the fuel (from 10:1 to 16:1).
Still the same !!!!!!

Mmmmm...it is asking for a stronger mix of petrol to compensate for air getting sucked in somewhere. Has it had a bump? Run it and squirt some wd40 around seals and see if the revs change (probably slow down as it will be running too rich with choke on) WD40 will temporary seal it.

[i]Has it had a bump?[/i]
No.

[i]Run it and squirt some wd40 around seals[/i]
Like around the crankcase/block/head/sparkplug? I'll try that tomorrow.