hot exhaust manifolds

[mtbinscotland]

Hello there.  Season has finally warmed up enough here in scotland so had my AS legend out last weekend.  Running great although the manifolds are getting extremely hot to touch.  The impeler seems just fine,  water is running through the system but obviously not enough of it. Temp gauge is hovering at 150 although im afraid to open her up on the loch in case she overheats...  Can anyone suggest any helpful tips to help cool down this issue. 
Thanks!