idle miss

'76 900 cc motor runs pretty well, but has a miss at idle. #4 fouled its spark plug (month old Denso's). Cleaned plug swapped it for #1 plug as a test. At idle if I hook up a timing light #'s 2 and 3 light up the timing light and it is a steady flash. #'s 1 & 4 flash but not regularly. However if I bring the rpm's up 1 & 4 do flash regularly. This is with a dyna S ignition and Dyna coils. Also #1 doesn't get hot as quick now as 2,3,4. So sounds like that plug is bad, but its only a month old. Seems odd. Also why the difference in the miss at idle and off idle? Ideas please?

Thanks

Perhaps you have posted in the right section as this sounds electrical. At idle, your bike puts out less voltage than at speed. It could be that the power feeding your coils is marginal at idle. To check, I would FIRST get a multimeter and with the bike not running, check power going to the coils. Put POS/red lead on the power lead on your coil and the NEG/black lead on a frame ground. With the meter in VDC scale, turn the key on. You should be getting about 12.5VDC. If it is significantly less, see the Coil Powering Mod in the Filebase. If you get 12.5 VDC, you next need to do the following... SECOND, put the multimeter in VDC and start the bike. At idle you should get about 13 VDC or a shade more. Rev the bike to about 3500 rpm and you should get about 15.5 VDC. If you get significantly less or more, you will need to run some tests on your stator and regulator/rectifier or their separate components.

Ok. Did the tests WG suggested. Voltage turned out to be 12 volts off, 13.4 at idle, 15.2 at 3500. Seems clse enough to me, but ir wouldn't be the first time I was wrong. By the way it is now in my profile but I did do the coil wiring mod as you suggest. (It made an immediate difference when I did it a month ago.)

Any other ideas?

Thanks

Voltages are right where they should be... lets beat this to death... when you put the Dyna coils on, you did use green coils? Did you put new wires/caps on? I don't use ND plugs... I use NGK. If you have new wires, buy a set of NGK B8ES and give those a try... Your heat range in the ND plugs might be the problem. You sound like you have enough of a handle on this stuff to use the right ND heat range but since you can't buy them around where I live, I have a lot more experience with NGK plugs. It sounds like you have firing problems at lower rpm and if you don't have wire/cap issues, and your new NGK plugs foul as easily as the ND, then it would be a carb related problem.

As always WG thanks for the response! Greens coils, new plug wires, ND plugs are W24ES-U which if I understand it corresponds to the NGK B8ES. They were recommended to me by a motorcyle drag racing buddy who swears by them.

When I fired up the bike a while ago to do the test, all 4 cylinders got hot equally quick when tested by the 'spit-on-the-finger-stick-it-to-the-header-pipe' test. Maybe I hadn't given the fouled-then-cleaned plug a good enough chance. If it continues to be a problem I'll change the plugs.

Is it just me but are the plugs/ignitions on these bikes sometimes just plain ornery?

Thanks