Across' first Canberra winter - not coping with the cold :(

What you say makes sense, so you have a hypothesis at least, now it looks like your options have narrowed and those carburettors are coming off, it may take nothing more then blowing them out with compressed air if blocked pilot jets are the problem.

Most screws on the carburettor body - bowl particularly, will be very tight and require a JIS screwdriver or impact driver with posidrive bit to remove without damage

It's not as daunting as you may be feeling, be methodical and remember to check things and change nothing, or only change one thing at a time and keep notes, remember to re-tighten carb boot seals properly when re-installing

 

here is the location of the slow jets

 

compression is something which can be tested accurately - that's a simple question to answer

 

I agree. Get a compression test done. If the numbers are low, a tablespoon of oil into the cylinder from the spark plug hole, and re-test. If the number is higher than before, then the problem is worn out piston rings. If it doesn't increase, you need to look at your valve clearances

 

I'd say it helped for sure. I think you might have worn rings, considering that as it gets colder, it gets harder and harder to start. As the temperature goes lower, metal contracts. So your pistons, cylinders, and rings will be shrinking and the gap between the rings and the bore gets wider. Translates to lower compression. If you are right on the lower limit of the spec, the hard starting in extreme cold might be a symptom.

One really cold night in sydney (got down to zero or so), I couldn't get my FZR going no matter what I tried... Had to get to work so I roll started it down a slight hill, and it went fine after that. This was before I did the rings and head gasket.

 

Fuel. Compression. Spark - these are the "big 3".

You've got fuel because it runs. You've obviously got spark - to be able to move forward you need to test compression. You could be chasing your tail with spark plugs/leads/other stuff and have completely missed the issue.

I reckon get your mechanic to do a compression test, that will tell you whether there is a problem with rings or valves. I'd bet on the latter which is an easier job. You can buy a cheap kit for $20ish off ebay and do it yourself - the engine has to be warm but after that it's basically doing what you've already done (remove spark plugs) then screw in the gauge and see what you get when cranking. Do it twice on each cylinder (2nd time with a teaspoon of oil down the plug hole) and record your readings. If you don't have a problem at least you can rule it out...

Something like "start you bastard" or a roll start will mask compression issues. Warm start means your metals have expanded, narrowing the gap between the rings and the pistons and improving compression. Cold starts are the opposite as has been mentioned. The fact you've done all this work is great as you're learning and probably resolving some other niggly bits but if your cold start issue remains - you are probably looking in the wrong place still...