Topic: running rich because of weak spark? bad coil? ... test results

[patpollin]

I'm trying to get to the root of a running-rich problem with my 76 550k all stock except exhaust modified to 4-1 into a late ducati twin muffler , and have 2 ideas of what the problem is-  1 need to rejet ( downjet) to account for different muffler
2- weak spark 
I'm trying to eliminate #2 before I get in to rejetting as the way to go seems to be  fix everything then go to carb adjustments.   plugs 1, 2, and 4 are black after a normal ride, I never need to choke starting up in fact if I do the bike will stall, and revving before the bike warms up chugs out big puffs of black smoke.  mysteriously plug 3 is normal light brown/white, yes carbs are vacuum balanced I'll figure out this problem after the rich problem, maybe a clogged jet or something.  note- carbs rebuilt last fall, drained over winter

To begin, my spark does indeed look weak, it is a small blue spark.  I know blue is good but small isn't as good as a big fat one.  so on to the details, I'm running a new 1-4 points and original 2-3 points with original condensors-all of which appear in great condition, I know that doesn't mean a whole lot for condensors- what would the bike run like if the condensors were bad?     
I also suspect the coil to be going bad- I've read as many threads as I could on checking the coil but I'm still not sure if I"m doing it right on the primary side  here are my readings
 
secondary coils
14.55
14.35   ...seems about right from numbers I find on this site

primary- measuring between the 2 black w/white stripe wires going into the rear of the coils, measured at the bullet connectors above the coil- I only get a reading if I set the meter to 2M and then its anywhere from .3-1.0, changes every time I pick up and put down the pointer things, and changes if I reverse measuring poles (switch red and black)
if this is indeed the correct way to measure primary resistance, those seem like terrible readings and the coils are bad, can anyone verify this?  if I'm doing it wrong how can I do it right? 

I also checked voltage at the points just for kicks
with 11.80 volts at the battery
I get 10.40 volts at the points-  should I have more like 14 at the battery and 12 at the points?  that could be a problem

for anyone still reading thanks for sticking with me - and thanks for any insight to these readings?  Do I have electrical problems, should I replace my coil? trying to avoid a premature coil replacement as another fellow in a similar thread ended up finding out was not the problem.  many thanks and cheers Pat

[TwoTired]

Check each coil from Bk/w to either yellow or Blue depending on coil. You should get about 4.5 tp 5 Ohms on stock coils.

The color of the spark is highly dependent on the atmospheric contents that are being turned to plasma.  Humidity plays a role as well.

If your coil primaries are ok (most likely), then clean and oxide that could be on your point contacts, gap them and set timing.

Check the spark plug caps for inline resistance.  Most 550's have 10K caps.

You have a 1.4 v drop between battery and coils.  It should be half that.  I suspect you have oxide resistance coatings on your interconnect wiring connectors and your switch contacts.  Clean them.

After this, you will need to address the blackedn plugs which is most likely carb induced.  Would you say you new exhaust has more or less restriction than the original?

What air filter are you using?  If paper, is it new or old and clogged up?

Valve adjustment done when?

Can you determine if any of the rubber carb couplers are leaking?

Cheers,

[patpollin]

sorry forgot to specify a few of those things- new UNI air filter
also forgot to mention I'm getting really crappy gas mileage even when driving it like a baby, around 25-30 mpg which from what I read is way lower than average for this bike. 
valve adjustment done about 300 miles ago-but cam cover is suffering from a fairly developed case of shaft wear, #1 cylinder intake shaft has migrated about 1/3 of the way up the view hole. 
spark plug caps are new 5k caps, all tested between 4.8-5.2- should I switch to 10K? 
would the connectors being at fault for causing this 1.4v loss be the ones in the connector zone above the coil with black w/white stripe to blue and yellow wires?  And which switch contacts do you mean? 
my guess about the new exhaust is that it is more restrictive only due to this rich problem but I have no way of telling other than what the bike is showing
I will report back when I test the rubber carb couplers- did you mean the ones between carb and engine or airbox and carb? 
thanks twotired

[TwoTired]

but cam cover is suffering from a fairly developed case of shaft wear, #1 cylinder intake shaft has migrated about 1/3 of the way up the view hole. 

Be aware that the cam cover wear also changes the valve geometry so that the cam lobes and cam followers wear abnormally and rapidly.  Best cure is to get a cam cover, cam and rockers from a 77 or 78 engine.

spark plug caps are new 5k caps, all tested between 4.8-5.2- should I switch to 10K? 

No, I wouldn't.  But then I don't know why some have 10K and some have 5K. 

would the connectors being at fault for causing this 1.4v loss be the ones in the connector zone above the coil with black w/white stripe to blue and yellow wires?  And which switch contacts do you mean?

Looking at the 76 wire diagram, power gets to the coils via this path;
Battery terminal to solenoid path. - two connections
Solenoid terminal to Key switch path. - Ring lug, Ring lug crimp, two connector blocks, fuse clip, main fuse,  fuse clip, two more connector blocks
Key switch contacts themselves
Then Key Switch to Stop-Run-Stop switch path. - connector block, bullet connector,
Stop-Run-Stop switch contacts,
Then Stop-Run-Stop switch to coils path. -  bullet connector, then the bullet connector at the coils.

The ground or 12V Neg return path should also be scrutinized.
Battery to frame/engine path - two connections.

Though not needed for coil power, you really ought to check the main return connection to frame at the coil mount.  The big green terminal and frame connection can corrode from age and phosphates from car wash sprayers.

Then there are all the other connectors in the bike that ought to be cleaned, too.  The connection resistance that is dropping the voltage is resistive and these resistors waste power in the form of heat.  You can lose 10-20 watts through these connections, effectively reducing your bikes charging capacity by that amount.  It's significant when you consider peak alternator output is 150 watts, and 30-50 watts at idle.

Your call.

I will report back when I test the rubber carb couplers- did you mean the ones between carb and engine or airbox and carb? 

Both.

Cheers,

[NGL_BrSH]

Patpollin: did you ever solve this problem?  I'm experiencing very similar issues.

[WFO]

Do you rule out a bad spark plug?