I went out for a sunday blap round, on my recently aquired sporty, & had a moment of " whats up now " as everything cut out, to the point of me thinking that I had a serious problem, or a long, long push.
I thought I would push the starter button, but thought I would be wasting my time, as it was such a positive stop. It fired back up, woohoo the harley gods like me today !.

I noticed when I undid the tank cap, it went schloop !, That cant be right can it ?

I have seen this before on some Harley Davidson motorcycles! It has happened to me too. Your bike pulled a vacume on the gas tank. What this means is that the negative suction in the tank would not let the fuel flow to the carb. It could be that the vent to your tank is blocked for some reason. Might need a new cap?

I was walking downtown one evening and in the median of a four lane street there sat a Harley Davidson bagger traffic flowing in both directions and this guy and his wife had no clue why the bike died. I walked over and asked a couple of questions and proceeded to take the gas cap off, there was a hiss. Told him to try to start it and away they went.

Sounds like the filler cap's vent is clogged. Clean or replace and you should be good to go.

Thanks. Been out of circulation for a while, with me injured wing. Had to have a re-break & set, but things seem a little easier now. Yeah from what I can tell, there's a good vacume, so will have a go with the cap eased when I get chance. It is suspect as it has had twin cap tank fitted at some point, & may be after market.
Rekon it's a low mileage year this year, but I'm gonna make it up next time hey !

Never had a Harley that went "schloop," but I had a had a Gold Wing that went doo-wop and then hummed a few bars of "Little Deuce Coupe."

It's the gas cap. I've had a few problems this year with caps on my Sportster. One of them was so tight I had to grip it with gloves. The next one spun when I drove on the slab. So far, this third one works.