Saving Old Seagulls

Once upon a time oh, last week, I picked up "IT" for a seller off E bay.
Got "IT" cheap enough
1975 Silver Century.
A bit rough looking, but hey that never stopped me.
Took "IT" to work (warm shop, still cold here in Penna.)
Cleaned the carb, cleaned re-gaped the points, yep got a nice blue spark, worked on getting the oil lower unit gear oil "pudding" out.
Took it out back to the dumpster, dumped the REALLY OLD SMELLY fuel mix.
Get it home, pulled the prop, tank of water, fresh 10:1 in the fuel tank, "tickled" the carb., 4 pulls it fired on full throttle.
Took a minute er 2 to pump water, but it did.
I ran it 3/4 throttle, every time I tried to drop it down to slow speed, it's start to stall out.
"Ok it has to "seat in", just get it nice and hot, let it get used to running again"
The "IT" stalled out.....
Sounded like a fuel starve???
Pulled the fuel bowl, fuel in there?? there is a trickle of fuel from the tank through the needle.
Sprayed the carb jet, nope clear.
Spark plug was dry...............
Bowl back on, wait a few minutes, tried to "tickle it".
Will not start................
New plug, check spark, yep nice blue, still no luck.
Took it out of the water ("too much back pressure"?).
I have the tank off, the fuel shut off out and cleaned it with card cleaner (didn't look bad but...), flushed the tank, (hopefully the screen was clogged with old oil and???
The tank is drying out, (hosed it out with water and de-greaser).
New fuel line, (clear to see if fuel is there).
I haven't tried it today, but.......
I read somewhere here, same problems could be head gasket???
Direction to go or ideas for me?
Thanks!
Joe
So many old motors, so few $$

Do you have access to a compression tester?
The type that screws into the plug hole, 2-3 pulls on the starter cord and hopefully somewhere in the region of 50 psi is ok. Anything less will probably need a strip down to investigate further. A good time to clean the waterjacket while you're in there as "IT" seems to struggle with pumping water at the moment? (all the usual suspects Joe, dont panick it's normal)

jon

I have a real nice compression tester, but, the S.G. spark plug threads are bigger than any threaded hoses that comes with it!
Somewhere I placed the spark plug with a adapter that came off my '69 Century when I got the new plugs for that, if I can find that plug and adapter, I'll can test it.
I got it fired last night, actually runs well in the bucket.
I've had worse looking bikes and old jeeps, so this is common with me, to take on a project like this.
It seem to pump water well, even at lower RPM, (I was worried that the '69 Century trolling on my boat would over heat cuz it was at slow rpm, but if it pumps like this I think I'm OK).
I started "IT" ran it for a while, then drained the tank and plopped the '69 S.G. in the tank to make sure that ran beofre I took it up north this weekend.
I did notice the difference in the compression (the '75 being weaker).
All was well, motors were humming, shop had that blue haze of 2 smoke oil, until.............
I place the '75 outside the shop to drip off after I had pulled it from the tank.
I heard that tell tale sick sounding noise- wind??- Motor suicide? "IT fell over.
I feared the worse, carb broken off head, head cracked, fuel tank bashed in, but all the broke was the plastic storm gaurd and choke plate, like into 20 pieces!
Well the list of replacement part grows................
Joe
So many odd old thing need my help!