1985 K100 starting issue

[ajschank]

Toronto isn’t too far from Michigan  but I did retest pin 6 and it does read proper voltage now ~12, sorry I wasn’t super clear earlier. I’ll head on over to that link and see what I can figure out!

[rbm]

Yeah, by K-bike, it's a pleasant day's drive. :)

Sorry I missed your confirmation of the proper voltage.  I skimmed over the posting.

Let me think more about the problem.  So it's no spark even though everything seems to be fine.

[daveson]

Is your bike the early version?

Mines the later, with the black/blue and black red at the front, and green/yellow at the back. I spose the earlier one might be different.

[The Mighty Gryphon]

1985 K100 with original coils?  Wouldn't be the first time the coils were a problem.  After all, they were only used for a couple years before being redesigned and replaced. 

I could see a situation where an internal breakdown in the high voltage insulation could allow a weak spark to short out in the coil under the compression of the cylinder but still give a spark across the gap of a plug outside the engine.

If everything else tests good, you might want to replace the coils.  The later version coils were pretty reliable, so I wouldn't hesitate using pre-owned units.

[ajschank]

Well in the span of about 2 hours after running into the pole barn to try literally anything, I matched my coil wiring as daveson mention, and bam we had spark. Next problem seemed odd, no fuel at injectors. Strike two, feed and return were swapped. Now it sits and idles, dies as soon as it gets some throttle but I’m sure theres information on here for that . 

[daveson]

Hopefully just a gungy fuel filter or something simple like that.

[Laitch]

So it's no spark even though everything seems to be fine.

In Reply #10 ajschank indicated there is spark but never confirmed the resistance of the coils other that asserting everything was "ohming out ok". That's when he went down the rabbit hole taking Vogel's guide, a Fluke tester and the rest of us with him. It's time for a tea party and accurate confirmation of coil performance.

[The Mighty Gryphon]

Look in the tank.  When the engine is running is there fuel spraying from any of the hose connections?  The only fuel moving around should be a stream from the return line.  Loose connections can leak enough fuel to starve the engine.

New fuel filter is NAPA 3032.  Don't use the hose that comes with it, it's not rated for submersion in ethanol fuel.  If the hose on the old filter isn't too hard or cracked you can reuse it.  Otherwise, get some 5/16" rated for submersion.  I'm sure someone with a better memory will chime in with the SAE rating.

You might also want to get a bottle of Techron fuel system cleaner.  Put a couple gallons of fuel in the tank(non-ethanol if you can find it) and about 4 ounces of the Techron.  Let the engine idle for a couple minutes to mix it and get it down to the injectors.  Let it sit for a couple hours and start up the engine and let it idle, rolling on the throttle occasionally.  Once the bike is roadworthy, take it out for a ride, keeping the rpm at least 4000.  If the bike has been sitting, the injectors will have a lot of crap i them, and unless you send them out to be cleaned it can take a while to get them loosened up.

[The Mighty Gryphon]

Going back to my earlier post regarding early model coils, keep in mind that a weak coil can spark into an idling engine, but when the throttle is opened and the cylinder pressures rise on the compression stroke it can fail.

Keep this in the back of your mind while you troubleshoot the fuel injection system.

[ajschank]

Thanks everyone for all the advice! I did get the bike to not die anymore when throttle was applied, apparently the previous owner deleted the vac hose that goes from the intake to the engine area(plenum?). Got a temp one on there it now it’s happy!! I’ve got a lot of adding things back before it’s road worthy, but of course I’ll keep everyone posted in the appropriate spot!