Tuning-coil questions

[ron2830]

Thanks for the help in my previous posts re synching the carbs. Got the dial vacuum gauges to stabilize/dampen by clamping the hoses with wire cable clamps, let me dampen them just to the point they wobble about 1/8 inch. Carbs are synched. Also found out the idle mixture screws were all over the place, one about 4 turns out, another 2, etc. Reset them to manual spec of 1 1/4 turns out. After synching carbs, checking timing (on mark at idle, around 31 at 5K, then reconnected vacuum and advances to about 60 at higher rpm. Cleaned plugs, BP6ES, gapped to .031 and now all are light tan to gray, not black and sooty like before. It runs better and idles much smoother but still have a little hesitation under full throttle between 4800 to 5200, then strong after that all the way up. Also notice a little popping occasionally while decelerating and at idle, not loud but you can hear it. Did not do that before. More questions:

79 XS1100 Special, aftermarket four into two exhaust into turnout mufflers, new K & N air filter in air box, pick up coil wires appear intact.

I was going to go to a hotter plug BP5ES to solve black plug problem but now wondering if may I should go one step colder due to popping sound, is this sound minor pre detonation? Along the same line has anyone tried the NGK Iridium plugs? They are expensive, but seem to provide hotter spark with the same coil voltage. I also have a set of new BP6RES resistor plugs from a car I had many years ago, can these be used or does this add more resistance that will cause problems?

Are the factory idle screw settings correct for older bikes or should I tweak them a little to elminate the minor popping at idle?

Checked my coils while the tank was off to sync carbs, primary is about 1.4 ohms, secondary on one pair is around 37K, the other about 30K. Discovered these have the resistors in the plug caps which are about 5K each, so subtracting 10K from each still gives me 27K and 20K which seems out of spec. Also can the resistors be removed and replaced with a piece of copper the same length to help with spark or are they needed for anything other than radio interference? Maybe the secondary resistance is the reason for the hesitation in the mid range under full throttle?

I have been using 91 octane premium gas, is this needed or any benefit to the extra cost?

Thanks for any comments, would be in the dark without this forum.

Ron

[xssiveone]

Are the factory idle screw settings correct for older bikes or should I tweak them a little to elminate the minor popping at idle?

Factory settings are for new bikes, and should be used as a guideline for older bikes. Start there, and if you think there is room for improvement, tweak away. You might even think about getting a ColourTune to set the idle mixture screws. It allows you to adjust the mixture to get the optimum colour flame.

[ron2830]

Ok too many questions....

got carried away with this post so let me just ask a couple of questions...

I am sure I have the carbs synched pretty well, set the idle mixture to factory setting, 1 1/4 turns out, but now have some random popping at idle and when decelerating.....could this be too lean of an idle mixture? Bike runs better but popping is annoying and I am concerned about detonation...Thanks

[Dennyz]

The popping is not detonation. The spark plug fires every 360 degrees (unlike typical 720 for a four stoke) of crank rotation on these motors. If any un-burnt fuel is hanging around in the exhaust side, the spark plug will light it off. If anything, you may be a bit rich. By all means, tweak the idle mixture to see if it goes away. Tweak one at a time, as all it takes is one cylinder to cause the popping.