Was the fault gradual or instant.

Can you pin the poor response to 1, 2 or 4 cylinders [remove each plug lead in turn]
Tight [less then zero] inlet valve clearances will do that.

If you fitted the carbs to a new engine, I would now be inclined to try a spare set of carbs.
Are they set up for a standard or RLR motor.
Dave.

The carbs were for neither engine, the RLR motor use to run ram air but ive ditched that in favour of a more standard setup. I fitted these NC30 carbs with modded needles, jets etc after taking the ram air setup off and the bike idled and run fine, i even have a video of it somewhere.
Without going into to much detail i then fitted a standard engine with the same carbs which run fine, this stayed in for about a 1000 miles and was then removed and the RLR motor put back in.

Going back to what you said about all 4 cylinders running, one of the rear pipes is slightly cooler than the other. On inspection the plug is black compared to the others which are as they should be, It does produce a spark tho and it makes no difference if i swap plugs round but when running there is a intermitant slight cough which is more noticable when i hold a hand over the left pipe(twin pipe system) which is the rear cylinders. So this led me to think coils, im running CBR600 stick coils so these come off and the standard coil put in its place which again made no difference at all.

Would a badly setup carb(too rich) be causing this slight miss fire on the one cylinder? I cant for the life of me think how this could have happened as i basically took the carbs off the old engine, placed them on the bench until i was ready to fit them to the RLR engine hence why reluctant to strip them down. Or could it be something on the ignition side of things playing up?

actually i had this or similar on a set of NC30 carbs and it turned out to the the air screw, some clown had only fitted 2 with the correct rubber orings and washers, 2 were missing completely.

I assumed the carbs were cleaned and adjusted when balanced.

If not, clean and check pilot circuits and pilot screw setting.

Do Honda set lean for emission tests?

Dave.

Yep carbs were cleaned,adjusted and balanced when i first fitted them to the RLR engine, as i said i see no reason why they shouldnt be ok as they were running fine then and run fine for a 1000 miles on the standard engine, for peace of mind tho im just fitting a set of known working carbs straight off another bike.

tony, have you checked you havent snaggged any of the carb diaphragms whilst refitting tops or somin similar, worth a look, a tear or snag could cause similar problems no. just clutching straws for you lol or even an airscrew o ring etc.

Carb diaphragms?

Just a thought but have you been trying your new Hrc slides in these carbs whilst they have been sitting on the side?

Sounds carb related and weak mixture [air leak, fuel supply/level]
Although the motor does run on all 4, do they all run at tickover.

If you can narrow it to 1 cylinder, it will be easier to locate.

With motor warm or hot, switch off and allow ex pipes to cool down.
Start up and run only at tickover for 20 seconds and switch off, check each ex for equal temp, same distance from each port.

Dave.

Revs hanging is a sign of a weak mixture, are you sure the pilot screws are set correctly?