Intermittent misfire

Hi all. Hoping someone may be able to offer some advice with this very frustrating problem. I have a 1990 model that has 140 000km on the clock, it still goes great(when its being good), does not use oil and doesn't blow smoke. Now here is the problem - first thing in the morning,when air temp is low, it runs great( smooth and revs clean. After it has been sitting work in the sun all day it runs a little rough(noticible vibration and flat throttle responce and sounds different).
I have taken the following steps to try and eliminate the problem
1 - new plugs
2 - new coils(probably nothing wrong with old ones but 20yrs of age)
3 - new fuel filter(did find old one seperated inside so wasn't a filter anymore)
4 - pulled and cleaned all connectons
5 - carby balance(probably not exactly right but better)
6 - found corrosion in the ends of the plug leads themselves so trimmed back to
fresh wire a reassembled(inspected plug caps, look like new)
This bike has had a fighter conversion done(not finished) and has had the wiring loom completely rebuilt by me so i am wondering about a broken wire somewhere but i really dont think so. Maybe blocked jet or crud in a float bowl but didnt seem to be anything when drained.
I am now at a bit of a loss so thought i would ask the opinion of people who know a whole lot more about these things than i do. Have thought about new leads and caps but at $193 each i am trying to avoid it
Any help will be greatly appreciated.

 

Wow the price on the leads are ?? This place shows them for $20 each. Not sure if you can order from the states without delays or $$. Check this place out. I've used them several times. Good to deal with.

http://www.shspowersports.com/fiche_section_detail.asp

 

That's a tough one. If you ride in cool weather, does it always run fine? Or does it act up after it warms up, period? Have you checked the valve clearances, carburetor boots, etc.? It almost sounds like you're dropping a few cylinders, so it might also be something in the primary ignition system (whatever it is that triggers the coils; I don't know VFR ignition systems). It could also be something in the charging system that is allowing the operating voltage to fall below the threshold value that the ignition system needs to function.

Most of the problems I've ever dealt with that are thermally related are electrical, but that's not to say that there isn't something mechanical going on (including carburetors/vacuum leaks).

 

Valve clearances have not been done but will be done very soon,this is something i have been meaning to do for some time. As for the way it acts up it now sems after riding it yesterday that it may just be coincidence that it seems to run ok when its cool as i left work and rode about 5km and it was playing up as usual, puled in to get some fuel, restarted and the misfire was gone. It also seemed to act up i the morning but only after poking along in top gear at about 80 for a while. I am really confused now, could it be picking crap up in the float bowls and block a jet? have drained them but may have to come off for a proper clean. Glad i love this bike so much, any other would be gone by now. By the way have any of you guy tried the new Pirelli Angel ST tyres, if not do they are fantastic. Heaps of grip in both wet and dry and great feedback through the bars.

 

OK so i have been busy this afternoon and pulled the front plugs to have a look, no 2 black and quite wet with a fair amount of crud built up, no 4 dry and light tan in colour the same as the back two so it would seem this cylinder is the culprit. Now to find out why. Will do a compression check and valve clearances but with 140000kms i am worried might be something more sinister.
I have also discovered another problem whilst the radiator was out, the lower rail in the frame(that the motor hangs on) is cracking behind where it meets the cast head section, is this a common problem does anyone know? will welding maybe a brace over this area help to stop this happening again? Again any help will be appreciated. Cheers.