The filter sits in the back of float needle seating.

The tap is vacuum operated, more likely flooding than air leak.

If fuel leaks/flows with tap on, the diaphragm valve is leaking, [but the float valve will shut off and control the level] but if leaking with tap off, then diaphragm could be split and fuel running down vacuum hose into no 3 cylinder.
Is no 3 cylinder poor?

Assuming that the diaphragms have not been removed as per HRC mod.

arsey30 wrote:The filter sits in the back of float needle seating.

The tap is vacuum operated, more likely flooding than air leak.

If fuel leaks/flows with tap on, the diaphragm valve is leaking, [but the float valve will shut off and control the level] but if leaking with tap off, then diaphragm could be split and fuel running down vacuum hose into no 3 cylinder.
Is no 3 cylinder poor?

Yes number 3 is the main problem. I can hear it have the odd pop when it fires every now and again on idle.

Sounds weak or dragging in air, so check the vacuum hose for splits, that would reduce the fuel flow unless the tap has been modified as above.
Make sure no fuel is flowing down the hose.

Does it cut in at high revs.

arsey30 wrote:Sounds weak or dragging in air, so check the vacuum hose for splits, that would reduce the fuel flow unless the tap has been modified as above.
Make sure no fuel is flowing down the hose.

Does it cut in at high revs.

From cold it on choke seems to chime in and get hot but on idle the pipe gets cooler again. Hi revs it didnt make any difference earlier. Removed HT lead whilst revving and no difference. The vac hose has no splits and quite sure no fuel flows down it but I will recheck tomorrow.

Also a friend of mine who had a VFR said his derestrictor unit used to cause strange running on his even at idle. Could this be a possible cause?

That's bizarre if you take the plug cap off I wouldn't of thought it would stop the other side firing aswell!!!!!!?????

Your fuel tap shouldn't leak fuel even if its turn on when its off the bike like arsey30 says so give that a rebuild too especially if its got the hrc mod which wont help a road bike.

Give the carbs another rebuild maybe spray some wd40 thru the passage ways and make sure theres flow through them.

Have you changed the plugs they are a pain in the arse too, maybe take them out and give the tips a good burn off with a cooker or a blow tourch.

I wouldn't of thought a derestritor unit would make any difference at tickover, try taking it out see what happens.

Cheers
Ian

It sounds very much like Arsey30 said on page 2 of this thread - carb blocked.

This is a common issue if carbs have been sat for some time with petrol still in them, the passageways are very small and when the petrol evaporates it leaves a gummy sludge behind which is hard to remove.

They can often only be unblocked via ultrasonic cleaning.

Do most garages do ultrasonic cleaning of parts?

The restrictor limits speed not revs, but if it is disabled with out a de restrictor then the cdi will cut the rear 2 ignitions around 5000rpm.
If it runs on choke, then I do not suspect not an ignition problem.

You can easily remove it to see if it makes any difference, a restricted bike will still rev out, the restriction is in the speedo head.

Have you established if the other 3 cylinders apart from no 3 are running correctly?
Your recent test blanking the inlets [if you did it 1 at a time ] suggest both rears not working well, the engine should run on 3 easily, and even 2 at a pinch.

This issue could also possibly be caused by throttle butterflies needing synchronising. i.e. cylinder 3 butterfly may be fully closed at idle.

To eliminate this as a cause you could try increasing the idle speed (via adjustor) to about 2000 revs. If the bad cylinder starts firing consider synching the carbs.

I have a possible theory lol. I'm going out there now to test it. May be complete rubbish but ill report back later!