SPARK PLUGS

1981 KZ 440 LTD BELT.
I have found the bike to be very 'cold blooded' & doesn't smooth out until really warm (hot) I am running stock NGK BR7ES,
A friend has suggested fitting 'hotter' plugs, any suggestions ?

Hotter spark plugs won't make the bike warm up faster. In fact, spark plug temperature range don't affect the engines temperature at all.

That is partly just the nature of a carbureted engine. You should be able to ride off within a minute or so, with the enrichener or choke partially on. Then after another minute or three, the engine should run just fine with the enrichener or choke completely off. If the engine runs really poorly, or you need to leave the enrichener or choke on for a long time, or if the engine runs so poorly that it is unrideavle until at full operating temperature, then there are other problems. A different heat range spark plug is not the solution at any rate.

Just ordered a brace of BR7EIX can't hurt to try + a touch of enrichment.

These IRIDIUM plugs have cut warm up time in half.

I'm not an expert in spark plug systems, but those resistor plugs might fry your coil if you still have the stock coil and stock caps. The caps have resistors in them (as opposed to more modern setups, which put the resistor in the plug itself), which will up the required voltage from the coil to get a spark. That voltage increase could blow out your coil.

You can certainly ride the bike on partial choke just fine. Adjust the choke position to get around a 1.5k idle, and adjust it down as the bike warms up (and the idle climbs). Once you hit the bump in the side of the carburettor casting (from the pilot jet), the bike should be totally rideable, just remember to gradually reduce the choke over the next few minutes.

You can also look at giving the pilot screws (on the tops of the carburettors) about a quarter-turn up (anti-clockwise) each. This will slightly enrichen the mixture and reduce the warm up time a bit. You don't need to go too far out from factory, as this will increase fuel consumption and may cause plug fouling if you go too far.

My usual routine when I go to start up in the morning is to pull the bike out beside the hood of my car (where I put my helmet and gloves), start it up, and get the choke adjusted so the idle sits between 1.5-2k RPM. Then continue to adjust while the bike warms up while I put on my helmet and gloves, and by the time I get all my gear on, the bike is warm enough to idle well with the choke at the position I mentioned (level with the pilot jet bump in the casting).

Make sure you have a stock exhaust too, and if you or a PO drilled holes in the back to make the bike louder, plug them up as that will lean out the mixture and increase warmup time.