Saving Old Seagulls

Hi everybody I have recently been working on a forty featherweight and sorted a few issues it was having.I have also converted it to run 25:1 but now it is back together I have a couple of issues:
1. I lose water flow on low revs and have to increase to get water flow to return.
2. when running around middle throttle the engine revs surge up and down without any movement on the throttle.

could anyone advise where I may have gone wrong or is this down to adjustments needed?

Water flow at low revs is to be expected, at low rpms the impeller will not pump water. The surging is caused by an inconsistent air fuel mix, first step i would take is checking the obvious ( all carb components are tight, fresh fuel correctly mixed, fuel filter is clean) My guess is it could be that the new needle has been set too low in its surclip, try raising it a couple of notches.

These motors rely on a good supply of oil to seal the main bearings. Using a reduced oil ratio on an older, well worn engine may allow the main bearings to leak, causing the mixture to fluctuate, hence the surging.
Make sure you use marine specific 2 stroke oil. If your main bearings are not in the best condition you may have to revert to a higher oil ratio.

Cheers, Mark