81 cb750f #1 cylinder intermittent firing......won't fire at idle, any help!!!!!

[bassproducts]

Ok, here goes. My 81 cb750f is almost there. Fires up fairly easily, but #1 cylinder will not fire at idle. Plug is slightly black, but not moist. Have been through the carbs several times, new plug wires, plenty of strong blue spark on #1 also,  replaced base gasket, head gasket and base cylinder O-rings. Have done timing and compression is #1 135 #2 150 #3 148 #4 150.  When I'm at idle I will open the throttle and it will rev to 4-5,000 rpm until I adjust down the idle screw on bottom of carbs, then it almost dies and I have to adjust back up. Getting ready to do valve adjustment on #1 to see if that will raise compression thinking that might help. Any advice would be very much appreciated. Please let me know if I might be missing something.... Thanks!

[shinyribs]

Is number one not firing, or just fouling the plug?  You verified that you have spark on that cylinder, does that header tube get hot when it runs? It might not be a no spark issue. A no spark issue will not produce a black plug since there is no combustion taking place to produce the soot.

[TOOLS1]

135 PSI is not that bad. It sounds like a carburetor problem. Could be a vacuum leak.
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