Lack of Top Speed in 5th gear

Hi, l have a 1984 KZ750L4 Canadian model that is completely stock pipes/airbox etc which l had an some idle issues with that turned out to be blockages in the enrichment circuit within the float bowls. Now the bike is runs and idles good but the issue l am now having is that the bike runs out of power in 4th and 5th gears and no matter what will not pull past 90mph. In all other gears the bike pulls to the redline. Just incase my 240lb weight was the issue l also had my 110lb wife take the bike for a ride and she also had the same issue.   

Valve clearances are good, leak down and compression tests showed perfect, carbs clean and balanced, clean air filter with no air leaks, both coils and all spark plugs have been replaced along  with the relay power modfication. I was thinking that the engine could be running lean so replaced the main jets from 110 to 112 but that made no diffrence.

Current carb settings are:
BS34 carbs
Main jet 110
pilot jet 37.5
needle Y270 (clip in middle)
pilot screw 2 turns out (have tired both in and out 1-1/2 that made no difference).
My altitude is 1600 feet


Thanks,

Is the ignition timing correct ?
Has the gearing been altered to lower the revs for highway cruising (sprockets changed) ?
Is there any damage to the exhaust collector that could be limiting flow ?

This might sound like a dumb question, but is your clutch slipping?

What did you recently change that has caused this. A wild stab, cam lobes worn and engine down on power and it can’t overcome the load in 4-5th gear. 

I purchased the bike back in the winter with an idle issue that the previous owner could not figure out, so have never rode the bike without a running issue.


I did check the timing after the valves were adjusted and it was correct, (Camshaft/timing chain/crank as per the manual). This model has electronic igntion and doesn't appear to be adjustable.

Bike still has the original chain and sprockets which l have confirmed are the stock ratio.

Exhaust pipes and collector has no damage or leaks, only minor rust.

Clutch plates have been recently replaced, clutch was slipping before but now doesn't which l suspect was due to the last owner using car oil with a friction modifier.

Cam lobes are in great condition with very little wear (bike only has 12k on the clocks)

Restricted air intake? What filters are fitted? If stock, when was the air filter last renewed. If pods are they quality pods in good condition? It sounds like you have a restriction in either fuel or air. 
Also if pods ensure they are clearing the pilot air take ports. Pilot jets are contributing for the entire rev range. 

Have you checked the float levels?....might just be running out of fuel under high load
 

Leaking old brittle carb boots can cause a lean A/F ratio!!! They are on the top of every bike "re-build-to-do" list!!!

Are you sure the bike is running on all four cylinders?