Scooterotica

I've got a SPAQ hydraulic outboard disc brake that is too good. The problem is I cannot get any real movement in the brake lever before the brake is locked up. I've tried getting air into the system so I can get some play on the lever to try and get some progressive braking. This works for a few miles and gradually the air goes out of the system - presumably it escapes into the master cylinder and I am back to where I started a brake that locks up with hardly any movement on the lever. The kit appears to have standard Nissin master and brake cylinders, the only difference from what was supplied and what i have fitted is the brake hose. I purchased a narrower diameter hose so I didn't have to drill such a large hole in my headset.
I have got a similar setup on another scooter, but the disc brake is a ScootRS one with the standard supplied hose. There are no issues at all with this. I can bleed it in the same way as the SPAQ one and the lever movement remains as set when first bled with a nice steady progressive braking movement on the lever coming to fully locked with the lever about 60% in.
Anybody got any ideas because I've run out of them

Have you tried it with a proper sized hose?

I'd expect it to be the size of the master cylinder, personally.

I think MMcL is probably right.
Sounds like an incorrect master cylinder. A larger dia. piston will move more fluid per mm lever travel. So will feel solid too soon.
The hose won't make any difference, it just connects two chambers. Letting air in is not a good idea.
What causes a difference in feel is the ratio of the two X-sectional areas, which tells you the mechanical advantage or the multiplication of your hand pressure by the time it gets to the brake pads gripping the disc.
It could be you have one from a twin disc setup. Will the supplier boogie on a replacement? So having considered that, they aren't desperately expensive, a bike breakers maybe? Does someone know the correct dia for the single disc/ double disc master cylinders?
You say Nissin, but I was looking for some pads the other day and there was any number of Nissin clone calipers and master cylinders, some with the name on, some without.

is the hose braided ?

if it is fit a standard one, if that dosnt cure it use 1 finger to brake

Can you file a little off the lever to gain more clearance from the m/c piston? Seen this a few times with these.