If you haven't checked fuel pressure, start there
If you haven't changed the crab cap, do that after checking fuel pressure
You threw thousands of dollars at it and never diagnosed what may be a $10 fix
Get new cap. OEM on the Champ HXs are stant.
Same puke bottle is used on everything from the ill-fated vaser to big blocks. If you add too much coolant, it spits into the bilge
Water tank fitting should say water.
However on a 35 year old boat, someone could have pumped fuel into the water tank
Could be second tank
Need to trace the hoses
I learned to work on carbs almost 50 years ago. I suggest getting an OEM kit (has instructions) or get the factory service manual. Also check out mikes carb site
Make sure it's a marine cam for wet exhaust
Do not exceed 270 degrees of duration.
Make sure you check the cam card to make sure no overlap
Have had good luck with the Comp cams XM264HR
https://www.compcams.com/xr264hr