Engine increases revs at idle, smokes after hot

Losing motivation and need some help, thinking about just selling ugh. I was having hanging at higher revs and slow acceleration off idle. Fixed throttle cable stuck open and seems to have helped some with hanging at higher revs but possibly not completely. Took the idle mixture screws out 3 turns to possibly help what I felt was pretty slow acceleration off idle. Not sure how much it helped or if I'm just not used to an old 4 cylinder bike. It still seems a little sluggish to start going maybe it's less torque in the lower range for a 4 cylinder from what I've read.  After 10 or so minutes of riding around the block when I would engage the clutch to let the engine return to idle, I would hear the engine rev up to the point where I was wondering if it would just go too high. Finally, after returning home saw smoke coming from the engine, was tough to see where from, but I did see bubbling from the valve cover gasket area. Attaching a pic to show. Don't want to take anyone's time too much, but just wanted to see if anyone had any ideas for any of these issues, just looking for some positivity. I'll try to spray some carb cleaner over the boots tomorrow and see how that goes did this before and didn't see any noticeable difference. 

1983 KZ750 LTD four cylinder 

Thanks,
Jakob

Creeping idle when hot is sign of lean condition, most likely an air leak.  Did you replace the rubber carb holder boots?  They typically leak after 40 years of use and spraying junk on them doesn't find the problem.

Actually being able to see bubbles coming from the cam cover gasket means there must be major crankcase pressure. Its not uncommon to get a weep from that gasket but bubbles is not right.  The only way to produce crankcase pressure is heat (if your breather is blocked) or piston blow by. Whats your compression readings?

3 turns out will mean you are running lean if they are airscrews (engine would be very very hot) or rich if they are fuel screws. Which do you have?

The bike uses CV type carbs and the pilot screws control mixture entering the carb throat.  3 turns open is no problem although for most bikes that will be somewhat rich.  

Thank you for the replies already. The previous owner said that he had an air leak from the engine block I believe somewhere and replaced all the engine gaskets... I tried to do a compression reading before and it was very low but wasn't sure if I did it right. I wasn't sure if I got it started if it would still be that. Will try a test again this evening.

On the mixture screw - that's right mine is engine-side for fuel. I might go ahead and order new carb boots. Is the bubbles coming from the cam cover gasket something I may have to take the entire engine apart to fix? A little worried there. 

Thanks,
Jakob

Compression test. How I do it is, all plugs out, tester in plug hole, spin the engine over with a good battery to get the fastest rotation you can, throttle must be wide open, take reading, do each cylinder in turn and note readings.

Thanks, will do this this evening and post the results.

Couldn't wait. New battery, throttle open, all plugs out:

1. 95
2. 115
3. 110
4. 70

Seems low. What are the takeaways? Valve work? 
Attached plug tips for posterity 1-4. Might align with indication of leanness since whitish color?

Thanks,
Jakob

Exact numbers can differ based on the type of tester you're using, but the differences in numbers seem a bit wide. It could be as simple as valve clearances being too tight...as for the plugs, they look a little light. I go for the "ideal" plug reading then another half turn out.

Dont know what they should be for your bike but on 650's they should be 160 - 180 psi. 
ive just had a look at an engine for a fellow enthusiast. His had low comp of 130 psi. When I checked the ring end gap with a new ring it was at 11 thou. Wear limit is 12 thou. Which promted me to do a bore measurement. His bores where oval and a round ring in a oval bore is the cause of his low compression. He had additional issues within the engine which made it uneconomical to salvage.

You comp figures, assuming they where taken with the throttle wide open, sound worse than his.

@ghostdive what does this mean: '"ideal" plug reading then another half turn out'? 
@ghostdive + @Warren3200gt - is this sounding unsalvageable already or do you all think it's worth checking valves or something else before knowing fully?

Thanks,
Jakob

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