1985 15hp Johnson won't idle.

[aussiechef]

Hi, I recently picked up a 1985 Johnson 15hp seahorse. It hadn't been used for around 3 years.
I have replaced the waterpump, fuel pump, new plugs and leads and cleaned out the carburettor.

The Motor starts first pull and is pumping water, but when I back off the throttle she dies. The motor revs fine when I use the throttle at the carburettor, but she just wont idle.

I have tried the idling knob in all positions but no luck.

Any ideas?
Thankyou.