suspect , sticking carb slides?

hi all, I recommison'ed this bike at the beginning of 2016, did a full nut and bolt rebuild ,except the engine, apart from putting valve clearances in spec. done around 2500 miles since.

cleaned the carbs, as per church.
bike starts and runs fine , both ticking over and on throttle.
my problem appears when the bike gets hot ,i.e. stuck in traffic, if I let the bike idle when its hot, then sometimes it will not then rev,
it will idle but not rev, I just get the "dull bluurrr" when I open the throttle.
sometimes it will pick up revs if I try constantly blipping the throttle, other times I have to pull over and let it cool, before it will rev freely . once the revs pick up she's away, and will run all day fine until, i'm stuck in traffic again,
if I constantly blip the throttle whilst the bike is hot , it will be ok, but you feel like a knobhead reving up.
I suspect the carb slides are getting stuck when hot. so iv'e just took them all out and cleaned them , and the bores, but no obvious signs , except a little scoring on the bores and slides.
anyone had this happen before, and anything else to check whilst its apart
thanks all
stu

 

hot engines like leaner mixtures. i would try turning the idle mix screws in 1/8 turn at a time and see what you get.
i could be all wet and you need to go out with the screws but the "hot" part of your description says it's too rich
i doubt the slides are sticking

 

Nice Bike !!! love yellow same as mine. ^^^+1 agree with Polock sounds like you are lean, or your float level could be off slightly . What do your plugs look like is it a tan or brown color ? ( good) white ( lean not so good) Blackish (rich not so good) Cheers

 

A rich mixture actually cools the combustion chamber. Lean mixtures cause the combustion chamber to be hotter (which is how holes get made in pistons). Since the problem only shows up when the engine is hot he may be too rich, but I'd like to see photos of the spark plugs first.

I'm thinking mixture as well, but I'm not going to rule out sticking slides from the slide bores not having enough clearance, or from air passages being partially clogged.

So, pull the plugs and give us pics. And we can go from there.
If you have the time you could go ahead and pull the tank, pull the top hats, pull the slides, and polish the bores (not the slides).

 

thanks for the replies guy's. though i'm a bit confused with some of the replies.
so I cleaned the carb bores with some fine wet and dry, (was carefull to seal the intake) also cleaned the slides with some scotchbrite and wd40.
went for a brisk (60 to 70 mph )for most of the way ,did 30 miles then got home and took plugs out
heres the first photo in torchlight

and heres another in daylight

so they do look a little pale.
also when I removed the carb hats ,the screws were'nt tight ,they were only snugged onto the hats, no effort at all to slacken them . maybe I forgot to do that, and its resulted in drawing air in when hot, thus not providing the vacuum needed to lift the slides?
I smeared some red rubber grease on the diafram tops now and tightened the screws.
its not warm enough to replicate the fault at the mo, so i'll have to wait till summer maybe.
should I tweak the mixture screws a little ?
thanks
stu

 

The plugs look good to me.
What say you all?

 

so most of your ride was on the needle and main jet, your concern was just off idle in traffic. that would be a idle jet adjustment.
the plugs might be a little rich but they are for sure old, that makes it kind of hard to tell.
now that the tops are snug, get some new plugs and go for another ride and let it idle for a few minutes before shutting down. now you can see what the idle mixture looks like.

 

Are these plugs right for your model?

 

ok thanks all , i'll do that "polock" but it may be a week or so.
yes plugs are old but I cleaned them last year, so what you're looking at are new deposits.
the sooting was just around the thread ends. the insulators and earthing tang are much paler, light grey,
I thought that would be lean!
thanks stu

 

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Are these plugs right for your model?
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yes
DR8ES-L
1989 xj600 euro modle
stu

 

Yep, they look a bit lean to me.

Even if you clean the electrode of an old plug, it won't perform as well as a new one. I'd personally change them to start with good reliable stuff.

 

On modern gas grey is not necessarily a sign of leanness. You need to look at where the color change is on the ground strap.
With a larger monitor I do thing they are a bit lean, but not by much.