DT40C tuning problems

I'm the guy who just put new pistons & rings in my motor and am having problems running it. It ran perfectly on land, so after 2 hours I finally got to running in seawater. I had to fiddle with carby but ultimately could only keep it running by manually controlling (and adjusting) the chock butterfly by hand. I obviously have a fuel/mix etc issue but where do I start ? Motor seemed to run best on half chock - what do I do ??
JUSTINTIME was on target when he suggested I had fuel issues so I especially welcome any further comments from him (or anyone else who feels they can help).
Bear in mind that what makes this problem more difficult is that its a manual pull start.

Was the motor still " stiff " when turning it with sparkplugs out??--------Is the throttle properly synchronized with spark advance ??---------------------Are carburetor jets and passages absolutely clean ??

carby jets are clean but maybe my problem is throttle link with timing (as you suggest). My motor is very easy to turn over with plugs removed.

At idle the throttle butterfly must be--------- CLOSED ----------and it must not open too soon when timing advances.

OK - at least it gives me a good starting point, because at the moment I've been starting and running it with throttle butterfly partly open - I'm 90% sure that my problems will be solved when I get these adjustments correct. Thanks.