Denys

So, the problem was in pilot jets and screws which I've replaced with a new set, idle is smooth right now without any erratic jumps... Adding macro photos with new jets on the left and old ones on the right. Thank you everyone for help!!!

I'm still thinking that the problem is with pilot jets (probably I haven't cleaned them enough) and pilot screws, a new set of which will be in my hands in 2-3 days, ignition unit in 5 days, actually those are the last items which haven't been replaced yet

Yes, I tried that, but the picture of erratic idling wasn't changing anyhow during TPS adjusting, the resistance of TPS is exactly as it should be according to the manual for open and closed throttle.

Revs was changing exactly in the same way even when air box with rubbers was disconnected from carbs.

Yes, I've already ordered another used ignition unit but it seems to me that box can either give ground to coils or not to give, there is no way that it can give bad or insufficient ground to the coils.

Sorry in previous reply I meant not spark plug but spark plug caps, I bought all 4 new and original exactly like this one https://www.bike-parts-suz.com/suzuki-motorcycle/assignment_spare_parts/3351048B10000 Position of camshafts vs cranckshaft is exactly as it should be according to manual.

In general I've sychronized carbs for three time, one time at low revs secon time at 1500 -1800 rpm and even third time with 0.05 probe as is shown here The video is in russian but the idea is to synchronize carbs more precisely with 0.05 mm probe. So in the end I'm sure that my rough idle is not because of the wrong synchronization.

Yes, I have. They are like new inside.

Spark plugs are new and original, resistance which they showed was 8.5-9.3 kohm. Yes, I've checked rubber caps with pressure and as well will 'starter liquid' - no leaks there. I've checked intake boots in exactly the same way as I did with carburetors rubber caps - no leaks. 'The wrong type of pilots screws' - they look exactly the same as the new original which I've ordered

got it)

or this one should be fine? https://www.gunson.co.uk/product/G4172/Motorcycle-Colortune-Kit-10mm

Yes I'm ready to buy Gunson colour but as I remember we have 10 mm spark thread, so I need to buy 10 mm thread adapter, right?

But on my gsx 750 inazuma aren't individual coils but two 'double-pin' coils, each for two cylinders, left coil for 1 and 4 cylinders, right for 2 and 3 cylinders.

How do you think, a little bit higher primary winding resistance could be the reason for rough idle, considering that secondary winding is exactly as it should be according to the manual?

That's exactly what I'm thinking, it is not enough just to have the hole in them but they should be ideally cleaned. Anyway I will try new pilot jets and screws and ignition unit (don't think the unit will somehow change the situation just bought from despair)