Re: last post
'82 55 with twin carbs and Prestolite ignition--one CD box, two coils mounted on the head? One piece lower unit? right?
I'm just thinking here. If you had a bad CD box or coils, it is unlikely that the engine would run well at high speeds.
These engines had surface gap spark plugs and because of the nature of the ignition system, when these plugs foul--even slightly, It is a bear to start the engine but yet it will run great at anything over high idle speed--if you can get it there.
So, first thing to do if you have not already done so is throw in a new set of plugs--L20V- I think the new Champion number is 332--Don't quote me though. And even if you have changed the plugs, if you still had the problem, you probably fouled the new ones, so clean 'em good.
Possibly a marginal stator would cause the problem because the power it puts out is speed dependent and is lowest at idle and cranking speeds. You would need to test the stator output to the CD box. You need a voltmeter that captures peak voltage (a regular vom will not do) and peak voltage at cranking should be 210 or more.
Next thing these engines --especially the two cylinder ones-- don't like to idle low. If the idle is set too low, and/or the plugs are marginal, they will stall regularly and if you don't put the control handle in fast idle, they just will not start--it's the nature of the beast. So: the next thing to do would be to buy a Clymers manual and re-synch the carb and ignition, and reset the hot idle to specs--about 700-750 in forward gear in the water.
Hope some of these suggestions help.