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b86 50hp Johnson intermittant ingnition on 1 cyl

S

Steve W

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"Engine runs great. Idles smoo

"Engine runs great. Idles smooth and accelerates nicely to full power. SOMETIMES. New plugs gapped properly. New 50:1 mixed gas (bypassed VRO). Rebuilt carbs. Timing is correct. The bottom cylinder is firing intermittantly and at random. I swapped coils and plugs separately and still had the same problem on the bottom. I checked for signal from the Powerpak with a timing light (No multimeter available) and there was signal from both coil leads. I'm assuming that the output from the powerpak to the bottom coil is there but doesn't have enough juice to trigger the coil everytime. If thats the case (and I realize that's a big IF), does that sound like a bad powerpak, or a flywheel equipment (stator, pickup,etc) issue?"
 
"I guess what I'm asking i

"I guess what I'm asking is whether the PowerPack amplifies the amperage into the coil, or is the impulse at full amperage when it enters the PowerPack. There is a steady signal from the PowerPack's lower cylinder coil lead and the timing's right on for both when induced from the PowerPack coil leads. Any help would be appreciated. Maybe a quick summary of how the trons flow from the flywheel to the plugs and what the power pack actually does."
 
"Roughly the system works as f

"Roughly the system works as follows:
The charge coils under the fly wheel charges a capacitor in the power pack.The sensor/trigger coils under the fly wheel gives signal to discharge the capacitor to respective coil depending on flywheel position. The voltage from the charge coils and power pack is around 250+ volts, the coils transform it up to 20k+ volts."
 
"Thanks for the reply. That c

"Thanks for the reply. That clears things up considerably. Since the discharge timing is correct for both PwrPk coil leads, it must be a charge voltage issue. If there's just one capacitor in the PwrPk, then what could cause only the lower cylinder coil lead to receive a lower voltage intermittantly - say 150v for the lower and the "normal" 250 always for the upper cylinder coil? Possibly an intermittant short downstream of the capacitor on the lower side? Last question. I know the horse is screaming, but your info is very helpful in zeroing in on the trouble area. Thanks in advance."
 
"There is only one capacitor i

"There is only one capacitor in the power pack, and to get less voltage to one cylinder I would gess on a faulty diode in the power pack rather than a charge failure, unless of course one of the flywheel magnets that passes the stator windings when charging the the capacitor for the 'second' fireing is defective. That is a loooooong shot!
There is however an other possibility and that is that the ignition works, but the lower cylinder does not get correct fuel/air mix for a combustion at higher rpm. This may lead to same symptoms as a ignition missfire. To check for this the best is to have a timing light with a built in tach function. Attach it to the problem cylinder and run. If missfireing, the rpm reading will drop. This is an easier and more relaiable way of testing than just looking at a blinking light. Might be difficult to catch a miss at 5000 rpm!
If rpm readings are the same on both cylinders, the problem is likely afuel/air mix problem."
 
"That helps alot. I'm 99%

"That helps alot. I'm 99% sure it's not a mixture issue, since the engine runs sweet when the cylinder fires. With a timing light on the plug wire it's obvious that there's no spark from the coil. Since it's intermittant, it's obvious both audibly and visually from the light even at low/mid rpms. I'll try a new powerpack and see how that works. Thanks again for for your patience with my beginner level questions. This site is a great find!"
 
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