Topic: Can of marbles in my engine!!!

[Vagelis]

Goodmorning gang,
 A couple of days ago I was going home after work, stopped at a red light and after idling for a couple of minutes the engine (CB400F) did a couple of 1,200 to 2,000 rpm jumps and died! I hit the start button and came back to life, or did she. At 1,200 (idle) it sounded like a "can of marbles" and ready to die, at 1,600 all was fine.
I went home took the carbs out and cleaned everything, checked the gas for water, nothing. Put them back hooked up the mercury columns, the vacum on #4 was at 46 the rest at 18! I synced them all checked the timing and took her for a ride.
The "can of marbles" (the noise sounds like it's coming from #2&3 carbs) is still there at 1,200 but with a steady idle, sync is fine on all carbs, at 1,400 rpm's everything is fine.
Any ideas?
One more thing I noticed that the #4 column on my sync thingy when it's hooked up has air bubbles! It's 15 years now since I bought it, should I change the mercury?What gives?
Thanks for the help, Vagelis.

[Chris Liston]

how about a valve adjustmant.

[bryanj]

Check cam chain sometimes those tensioner blades will snap

[eldar]

On a problem like this, I would look at mechanical before carburation issues.

Check the valves and even pull out the tensioner and visually inspect it.

Guess I am just backing what the others said.

[Vagelis]

Saturday morning I checked the cam chain & valve lash. Everything was like it should be. The "marbles" were still around. Sunday I went for a 2 hour ride on the highway, when I stopped some of the "marbles" had disapeared! On the way back I took the long and winding rode through the mountains, pushing the red line alot. On a straight hitting the reds the motor sturted to stutter, it spit a couple of times through the carbs, and went back to normal!! The marbles are gone at idle!!! Any ideas? 

[dusterdude]

sounds like you picked up a little trash in your carbs and when they spit the stuff was spit out of the jet or wherever it was,of course i would feel better if carb guru bob would check me on this.hi bob,im back.