Gradual Loss of Power and Plug Cables

[Rabbit]

The 74 Honda has been working like a charm for a month. Had it on the highway a couple times at 85 mph with power to spare.
However, I was driving round the city and experienced what I would call a gradual loss of power. I was in traffic in 3rd or 4th gear. It was hot. Was carrying my kid so the old 550 was working hard I guess. As I geared down coming into the toll booths it started to bog down if you know what I mean, the rpms dropping steadily off despite gunning it. It stalled right in the booth.
There was plenty of fire but each time it restarted it tended to stall. The only solution was gunning it and we did get it going long enough to get off the highway.
After sitting by the roadside for 20 minutes I tried her again and she seemed fine so we quickly headed for home.
The same thing happened 5 minutes later but luckily we were only 5 minutes from home by now.
After the engine cooled down I pulled all 4 plugs. They all had a little black hardened soot on them which was quickly wiped off with some steel wool. Number 2 was worse however and was also a little wet. The carbon seemed to extend up the thread of the plug a bit where it had not done so on the other 3.
When I was putting No 2 back in the cable/wire came off the rubber cap bitty. The exposed wire looked blackened. The plastic was not melted. I cut back a little and jammed the wire back into the cap and snapped it back onto the spark plug. The bike started up as usual on the first try and ran for maybe 2 minutes this time before dying. As before I could restart it but it dies each time.
Questions
Is the broken wire my only problem?
Can I simply cut more of it away and jam it back into the plug cap?
Do I need to replace the wire? I am guessing not any plug wire will do?
If so do I need to replace other associated bits as well?
Someone said coils may need to go too?
Once again, any advice or leads would be much appreciated.
My 13 yr son thinks I am crazy to want to tinker with an old bike.
I want to convince him this is part of the charm.
Cheers

[Blue]

Don't get too set on the idea that you have an ignition problem.  Loose leads don't help anything, but it sounds to me more like you have a carburation problem.

Are the carburettors fitted to the bike the original standards? Have the jets ever been changed? It sounds to me like the problems of oversize jets which allow fuel into the venturi faster than the float bowl fills up

Just an idea, i'm not a whiz on this particular bike, but 'leave no stone unturned', ey?

Good luck,
Blue

[Rabbit]

Thanks Blue. Yes these would be the original carburetors.
I put the plug wire and boot back together and that now seems satisfactory.
Bike still won't run for any length of time however. If it falls below 2000 rpm or thereabouts it stalls and is difficult to start.
If I keep it abouve 2000 rpm by gunning it then the engine continues to run.
I note that when I bought the bike it had a 'flat spot' at around 4000 rpm in lower gears which produced a minor and temporary bogging sensation which was quickly overcome. The previouos owner said he thought that might be related to dirty carbs as well.

[Blue]

This is a four-cylinder isn't it?  Do you have the correct vacuum guage for the four?  If you don't i recommend you take the bike to someone nearby who does and have the carburettors tuned and synchronised.  Also it might help to pull the carbies off and give them a thorough clean.

Effectively, my advice at this stage is to give the bike a good service; carbs, ignition timing, valve timing, tappet clearances, cam chain tensioner, oil; the works.  Even if these actions dont stop the bike from running poorly at this stage, it's something that will sparkle the engine up a bit when it is back to normal.

as i say i dont know much about 550 hondas, but if you're getting a good spark at the right time, the only real possibility must be the carbs - slack cam chains can affect things badly, but not usually in this manner.

heres hoping you find the issue,
Blue

[Cleggy]

Good advice from Blue.

I have a 400/4 and I've had to start from basics with it as I didn't know it's history and assumed things were right............how wrong can we be.

If I were you I'd have someone take a look at it for you, who has the right gear for the job.....I.E diagnostic gear/vacuum gauges etc.