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Bit of backfire

motogtp

CB750 Addict
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Des Moines
I have a stock '78 Super Sport that I have been "cleaning up" for a while. I have gotten lots of great input via this forum. It has always run rich although it is slightly better than when I got it (plugs always have a black, fluffy coating). I found that the jets were two sizes too big and the floats were installed upside down. All that has been fixed. I have been through the charging system (good), oil system (good), running a CycleX ignition, carbs were just synchronized, idle jets are 1/2 turn out, and I am even running air pods. But the plugs still come out black. I can wipe if off with my fingertips, except for the insulator. It starts and idles well (and steady) but I do hear a faint "pop" in one pod every once in a while. Today I held it at 3,000 rpm. After a few moments the rpm's fluctuate a bit (maybe 100-200 rpm) and I do get the occasional "pop". Needle problem? Boots? Burning oil? I love this thing but it looses power after a few miles and I want to ride!
 
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