Z1300 SMOKES.

Leak down testers will indicate leaks at-
the intake or exhaust valves, by air leaking at either the carbs or exhaust pipe
the head gasket by air bubbles showing up in the radiator or an adjacent cylinder
the piston rings by air leaking at the crankcase vent or at the oil fill cap.
Leak down testers are basically 2- 100 psi pressure gauges with a .040" orifice in between the 2 gauges. air is supplied at 100 psi in the inlet gauge and then the air flows through the orifice to the cylinder being tested. As long as all of that cylinder leaks are less than the amount of air that can flow through that .040" orifice, pressure will build and show up on the second gauge. Usually the second gauge is labeled as a percentage of leak down but sometimes depending on the manufacturer it's simply another 100 psi gauge.
So lets say you supply the tester at 100 psi and read 95 psi on the second gauge the result is 95/100 or 95% so the leak down would be 5%.. On some leak down testers 95 psi would "read" 5% leak down, 90 psi would read 10% leak down etc.
10% leak down is considered a tight engine. 20% would be up for consideration as to what repairs are required. Over 20% is a tear down for sure.

My preference is to do the test at top dead center but one has to guarantee that the crank is held at top dead center mechanically. I've seen the crank flip over if it's not held. (ask me how I know) Testing at top dead center is the area of the cylinder where most of the cylinder wear has taken place. Results taken at top dead center are quite different than results taken at bottom dead center.

Leak down test perfect all 6. Fitted viton valve seals pressured up each pot with said tester and bought a normal lever action compressor to do collets.
Still smokes like a bonfire. Some say precision hone and new rings, some say hone and fit chunky CB750 rings. Lot cheaper even allowing for piston machining. Others say hone and fit the Cruising Image big bore kit. ,£227 delivered plus taxes...
New pistons and rings and head gasket makes 1370cc
Will sell bike off to get rid, or need someone knows what to do another daft money.

Anyone knows a decent guy to sort it at realistic money let me know.

Please don’t give up!

Have to pursue it as too much invested for a non runner. Local engineer will hone and fit cb750 rings if give him loose parts. Can do within the week. I would prefer lot better mechanic than me to put back together though.
Lot of firms advertise, but need recomendation.

there is a crankcase breather on the left side of the crankcase that goes into the bottom of the air box you can see it in the picture with the cat siting on the seat have you tried running the bike with that disconnected from the air box as weird as it sounds maybe for some reason you are drawing oil up into the engine that way check to see if any oil spatters come out of the outlet on the crankcase (won't cost you anything other then your time) if you do try this allow enough time for the oil in the exhaust system to burn off

Just a thought on my part here. One of my 13's used to go through a lot of oil so I just ran a fuel line out under my seat and plugged the airbox hole (with an inline fuel filter) it stopped the excessive oil consumption for me.