FZR 2KR WONT REV OVER 10000 WHEN IN GEAR

Hi Guys,
Names Jake Im New to the forum here I have recently become a owner of a 1988 FZR 250 2KR its non exup not sure if it was before hand as it has a custom exhaust from the headers back. Anyway bike is running fine sounds great but im having a issue getting the revs up the bike will rev to redline while in neutral but once ridding its as if I am hitting a limiter at just a tad over 10,000 RPM Ive heard this is where the power starts so im keen to get it sorted out, After reading the forums I have found other riders have had this issue when changing to pod filters but mine is running the stock airbox and filter. When I brought the bike it had been sitting for a year and took a few good open runs to clear er out and get number 3 cylinder firing up after this I thought it'd be a good idea to check the oil so I dropped it all out there was 800ml too much in there not sure if this would have caused any damage and god knows how long the previous owner was running it like this for it was a very dirty color so I'd say it has been a fair while.
Anyway I have planned to run some injector cleaner through the fuel, ill be checking and gaping the plugs checking the tank vent tube for blockage and making sure the pilot screws are set at 3 turns out,
Is there anything else I should be looking into checking or any tests I can do to isolate the cause.
Thanks.

 

Thanks for the replys I'm confident the head gasket hasen't gone like I said she runs and sounds fine theres no chugging flat spots or other funny stuff untill it hits the 10,000 mark, the exhaust goes from 4 to 2 then into 1, I thought they all were 4 into 1 ? Anyway ill definitely pull the carbs for a clean does anyone know what the float height should be ?

 

Ok so cleaned carbs checked plugs and leads, might be running a tad lean going off the colour of the plugs, brought a new battery as I thought I had a dud one as it wouldent hold charge after 2 days of use charged and installed new battery and went for a ride still wouldent rev past 10,000 stoped off at the shops and went to start er up again and got nothing the battery had been completely drained so off I went roll starting it down the road I had to keep the revs up when indicating as they wouldent work otherwise, so now im thinking it may be an electrical problem contributing to my rev problem , any suggestions or a process of elimination I can carry out to find the problem? I have very little electrical experience so I have no idea.
I will post pics of the exhaust system tomorrow. Thanks

 

Hey guys attached some pics of the exhaust system couldent be bothered taking it off again so just took a few along the length of the system pics 1 and 2 show under the bike where the header pipes have been extended and join into two single pipes as seen in pic 4 then these two pipes join to a collector just before the silencer. I have a new RR here but the one i took off was a 6 pin the new one is a standard 4 pin can anyone tell me which coloured wires are supposed to go to which pin. Cheers

 

I have 3 yellow wires coming from the stator 1 red wire I presume from battery positive and 1 black which is grounded to the frame. So five wires only four pins and no diagram.

 

Ok so got the rectifier wired up and took some readings with the multimeter and this is what I got.

Battery 12.5v
Battery at 4000revs 12.8v

Voltage at all combinations of white wires from stator 31v at 4000revs

No amperage between negative terminal and negative post.