Are the spark plugs sooty black or oily? Sooty black could be ignition related from poor spark.
Redo the spark plug wire connections at all points. Doing so solved an intermittent firing problem on my 650. Unscrew the ribbed compression boots at the coils to disconnect the plug wires there. If the wire is dull from oxidation, nip off the ends a tad. Or go ahead & install new spark plug wires. Also, clean up the igniter leads on the cols. simply disconnecting & reconnecting helps.
Coils. A simple test is to ride the bike at highway speeds, then stop & feel the coils. press hard with your fingers. they should be warm, not hot. my neighbor has the same bike as mine & his coils would only get warm, while mine were getting very hot to the touch. So I got a pair of green Dyna coils & spark plug wire set from Z1Enterprises.com. The new coils solved a high speed miss & running problem. I think the grey 2.2 ohm are a better match for the stock ignition system, but the green ones are okay to use.
Fuel related. Also, make sure the tank is venting & the petcock is working right. you never know sometimes.
1981 KZ650-CSR. Competition, Sports & Road.
Last edited by martin-csr; 01-13-2017 at 08:26 AM.