GPz750A 85 Jetting

Hi Guys, This has probably been covered before, but I'm after a bit of advice.
Stock air box & filter
4-1, Unknown manufacturer & looks like its been shortened at some point, I do not it still has a baffle (not straight thru)
NGK BR9ES plugs (New)
Stock ignitor box ( but considering going to a GPZ900R unit)
Carbs fully cleaned
117.5 Mains
40 Pilots
Fuel screws 2 1/4 turns out
The bike fires great on the choke, settle to a really nice tickover off the choke & pull clean up to about 5k in top gear on an open road, this is when it starts to stumble, the best way to describe it is that it felt like it was starting to seize (I seem to have good oil pressure), She then ran OK again but seemed to be getting REALLY hot.
Pulled all plugs & all look the same (See example photo).
Any ideas ??
Cheers.
Phil.

Does the bike pull strong up to redline in the lower gears? Is all the maintenance such as valve adjustment up to date?

Probably not your main issue, but #40 pilot jets is a little on the rich side. Stock was #37.5. I briefly tried #42.5 in mine, but it would barely run. I’ve got a stock air box and filter but an aftermarket exhaust as you do.

As Ed said, start by checking valve adjustment. Be aware that the manual has a typo regarding the torque value for the camshaft bearing caps.

Nessism wrote: Does the bike pull strong up to redline in the lower gears? Is all the maintenance such as valve adjustment up to date?

To be honest, once it started misbehaving around 5K I didn't want to push my luck by going higher. she felt really good up to then but needed a bit of nursing home.
Good call on checking valves as not done for a while, I also suspect the airbox to carb rubbers are leaking a bit. ordered some new ones & might try to 'mod' the airbox to make it easier to get the carbs off when needed.

Not gone for a test ride yet as I'm going to hang on until the new airbox to carb rubbers turn up, but I think I may have found the smoking gun....& it seems to be my fault, bugger.

Took the carbs of to lift the needles a notch & #1 carb needle was sitting on above the plastic retainer ring, should be underneath (obviously) so #1 was happy on the pilot until the slide starts to lift & the already 1/4" too high needle prematurely lets fuel into the mix, plus nothing but gravity & vibration to push the needle back down hence the continued rough running.

I still lifted each needle 1 notch, now 2nd from bottom groove, to richen the mid range but a test ride will hopefully tell me more. I'm certainly getting a better understanding of how carbs work even if i fek up putting them together.

Cheers.

Phil.