What is the back story with your fe, is it a bike you’ve purchase that already had this problem or is it something thats happened recently
I bought it earlier this year. I didn’t notice the problem initially but I think that’s because I only did a few runs at lower revs while getting used to it, so I think it was a pre-existing problem. It had been sat for sale on Marketplace for a few months before I bought it. Pretty sure it hadn’t been ridden for at least 12 months prior to me getting it, maybe more. The cooling system was completely gunked up and the expansion bottle was half full of solid goo, flushed the whole system and all cleaned out ok and it doesn’t overheat even standing still in traffic. The fans kick in when needed and quickly bring the temp back down to normal. It had a fair bit spent on it about 2-3 years ago according to the receipts I’ve got, but generally parts that would be consistent with it sitting around for a while. I’ve now changed all the ignition components as well as fuel filter/fuel lines/air filter. The fuel pump checks out and is delivering the correct quantity of fuel as per the manual. The tank is really clean inside and no debris present in the fuel filter. Not sure where the tank vent is but I’ve been up the road with the cap open and still the same problem. Carbs have been stripped, jets removed, floats checked, everything ultrasonic cleaned as per previous post, re-assembled and set up as per manual inc. balancing and fuel mixture setting. I bought it on a whim as it was cheap, but I am now a VF convert, it’s an awesome bike, just got to get this issue sorted. I’m going to pull the carbs again this weekend and go through everything to see if I missed something. On a positive note, the carbs are easier to get off and on than a lot of other bikes I’ve had!
When you remove the carbs for cleaning i would just check a few things just to make sure a previouse owner hasnt fetted a mixed set of carbs…
Check all the ID numbers are the same, also , what size main jets are fitted,
Are the slides steel coloured or black, and does the carbs vent into the air box or to atmosphere.
Pete has raised some valid points,what serial numbers are on the carbs?
All the carbs are 82A, which I believe is correct for a UK bike. Slides look in good condition with no discernable wear. The carbs are currently stripped again and being run through the ultrasonic at 60 deg for 30mins/side. I made sure none of the parts were interchanged when I stripped them previously. However, I didn’t check the main jet sizes etc. at the time assuming they were correct. On closer inspection this time round, 1 & 2 carbs have 150 mains, and 3 & 4 have 145’s. At some point in the past it looks as though someone has assumed they were all the same. I will re-assemble correctly with 145’s in the rear carbs, and 150’s in the front. Also, the diaphragm springs were incorrect, with carbs 1 & 2 having the longer springs fitted. Again I’ll make sure that 1 & 3 have the shorter springs. I took a pic of the carbs before my first disassembly which showed the air vents venting downwards towards the engine. I now realise that is wrong and they should vent through the holes provided for them in the plate that holds them altogether, into the airbox. I won’t be able to get them back on the bike until tomorrow but I’ll update progress then. Fingers crossed!
You are onto something there mate,all those little things may well add up to the problem.
Regards Bif
Fixed! So you were right and it was the carbs all along! Not sure if it was the jets, springs, air vents or all 3 contributing, but it now revs cleanly all the way to the red line 
Shame I didn’t take more notice when I stripped them in the first place. At least I’ve got a bunch of known working ignition parts in case of future problems. Anyway, thanks for all the help and guidance, much appreciated. I’ve got another couple of issues that need investigating in the future, but I’ll start new topics for those as and when. Right now, I’m off for a ride!
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Result… 
Smithy.