My genoa halyard on a Carter 30 is very hard to hoist, even when I just put a tape measure up I had to use a winch. It has a line to the cockpit, the deck organiser block is not great, the block at the base of the mast ok. Even when hauling straight out of the mast it is too much.
I thought it could have come off the sheave or be a stuffed sheave, but there is not too much resistance pulling the halyard down.
I can't quite see well enough to know exactly what is at the top of the mast but would appear the halyard comes out of a sheave in the mast, then it looks like it is led down to a fairlead ( I think this is to get a better angle for the furler?)

From what I can see the halyard rope appears to be in reasonable condition.

Anyone know why a halyard is able to be lowered but difficult to raise? The only thing I can think of it is is twisted in some way around another halyard inside the mast. I didn't think at the time to check if the other halyards are being pulled or any extra tension on them when the genoa halyard is raised.
Trying to get this boat in shape to bring to Sydney (from Brisbane Water)

A similar post at the first one below where all the possibilities were mentioned and it turned out that lube spray on the furling genoa luff full length and on the head swivel of it sorted it out. Sounds like the halyard was twisting as it went up and the genoa luff was rough. A good read at the below 1st link detailing all the potential issues but the fact that your halyard is tight when hoisting with virtually nothing on the lower end but it lowers reasonably freely indicates it is more likely a masthead sheave seized or not rotating freely at all combined with internal halyard wrap/s as you suggest. An internal wrap of halyards around each other will create very large forces needed to hoist as they wrap around and bite into each other.

The 2nd link below summarises common furler issues which you would be aware of.

If you halyard is becoming twisted as it goes up as well as being internally wrapped around another one or more, then that's no good either.

Is the halyard reasonably supple taking the sheave bend ok? Is the fixed fairlead just below the masthead sheave well open with good clearance and clean and not damaged and providing minimal resistance?

As you say suggest you loosen all the other internal halyards (kite and main) and topping lifts (kite pole and main boom) and see which one or more moves as you hoist. When you haul the genoa halyard tail and head ends held in each hand down and up can the top masthead sheave be heard rotating?

forums.ybw.com/index.php?threads/hoisting-furling-genoa-problem.390167/page-2

www.sailmagazine.com/diy/beat-the-wrap-2

Had similar issue . Masthead sheave worn , halyard was between sheave and pulley frame. I reasoned that it was hard to pull up and easier down because of the
angle of the halyard on the axle ie hoisting was pulling halyard in the mast straight down on the axle whereas halyard coming out on a more obtuse angle the other way.

Have seen polyester halyards run through mast head sheaves originally designed for wire rope of a much smaller dia. Starts out alright but over time the rope swells and clearances run out.
Mouse the halyard with a smaller rope and pull it through the sheave to determine if the sheave is free on the axle or the halyard is too big in dia.

Get a friend or partner to pull you up the main halyard and check the genoa halyard out. Take a GoPro or cheap camera up with you as you may not be able to get high enough in the seat.

People like it better when I pull myself up the mast and they just follow me with the halyard. Grab onto stays and close in to the spreaders. Good workout and much faster.

If the boat is old I would mouse a new set of halyards - even before I went up the mast. Get some 10mm spectra for the main halyard, replace it, and then it will be safe to go up on. Then you can check the sheave.

Alternatively - you can use a kite halyard friends mast from a bigger boat to lift your mast out with. Then you get the mast down on your deck and can check everything out easily. New VHF cable, check lights, redo rigging, then hoist up mates mast and re install.

Problem seems to a solved itself, I'll put it down to the forum's help as I think thinking about the problem a bit deeper so I could ask for advice I was on the right track about the halyards possibly being tangled. r13's suggestion following on from my initial thoughts to loosen the other halyards was probably right on the money. I pulled the other halyards and topping lift down a couple of meters then when back to the genoa, it was running smoothly already. Pulling alternately at both ends, it was very easy. I had never pulled down on the spinnaker or topping lift before, so pulling down these might have untwisted something.
When pulling the genoa halyard I couldn't hear the sheave above the noise of the friction of the rope against the exit at the mast. It would appear the sheave is in better condition than I thought, although it still could be before that the rope was between the sheave and frame and righted itself.
I do plan to climb the mast and check it all out, will definitely get a new halyard, though my main does look fine it has unknown history.
I would love to unstep the mast but don't have any friends with a boat and certainly not a larger boat. It's a keel stepped mast so I think that would be difficult especially putting it back in so I think that will have to wait to do with a crane.