Misfiring at low revs after bike warms up

For the first few miles my Hornet runs just fine , but as it warms up it
starts to misfire at lower revs. At higher revs it pulls just fine and runs
without problems. Obviously the simple solution is to use more throttle but
something isn't right that I'd like to get fixed.
As the bike gets warmer the point at which it's fine moves higher up the rev
range. This started a few months ago when it would misfire below 3000 revs
once fully warmed but it's got steadily worse and now it's more like 5000.

I've had it suggested that it's the HT leads on the way out (it's 6 years
old now) so I'll do them next time I get a free warm weekend along with the
other routine jobs I've got planned.

Anyone care to agree with this diagnosis or suggest alternative causes?

 

I'd suggest a look at the pilot jets and/or their settings.

 

More likely just the plug caps, surely ?
The 900 behaved similar when the little rubber bits started to let water
where they shouldn't.

 

Are they likely to slowly deteriorate over a couple of months?

 

Quite possibly. I just roped the whole lot together in my mind

 

No.... but if they've got partially blocked, the blockage could build
up, so er, yes.

 

It's done less than 6000 miles [1] and has been serviced regularly , so I'd
not expect that to be an issue.

[1] It had spent a lot of time sat in someone's garage before I got it

 

Well , yesterday the weather was decent so I thought I'd have a nose.

First thing I spotted was a split in the fuel hose from the tank down to a
T-piece which I've had to order.
The more significant thing though was that the metal plate that runs across
the set of carbs for the choke adjustment was bent out of shape on the left
hand end and had detached from the carb leaving the once cylinder stuck on
full choke and the rest operating normally if a little reluctant to
disengage.

A swift twatting wiv an ammer and a few squirts of WD40 had it all
reconnected and working smoothly.

That would seem to be a likely cause as it ran fine when cold when the choke
would be needed but once it's warmed up and the choke was off on the three
cylinders it would be overfuelling the fourth.

Only trouble is I've now got to wait until the replacement for the split
hose (which I made worse) arrives and I can re-assemble the bike.