Left cylinder stops firing after engine is warmed up.

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Triangles
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Left cylinder stops firing after engine is warmed up.

Postby Triangles » Tue May 16, 2017 4:09 pm

So this problem started last fall after my bike had set for a while. At first if I rode it with the RPMs up I could get the left cylinder to come back to life. I took an extended ride for about an hour and slowly the left cylinder began to work again. This then degraded into the left cylinder intermittently not working. The odd thing is that it fires just fine on both cylinders until it is warmed up. It has degenerated to the point where it now will run fine on both cylinders until warmed up then the left cylinder is dead. It afterfires and back fires which assume is gasoline being pumped thru the left cylinder igniting when it shouldn't be. I was planning to tackle this over the winter but I just never had the time. I had initially assumed it was carbs from sitting but now am leaning toward an electrical issue. It could really be a multitude of things. I'll start with electrical since that's the easiest to check. It could also be a valve problem or an issue with the timing chain where the timing is off just enough that the left cylinder won't fire. Or maybe it could be the carbs after all... If anyone has experienced a cylinder not firing after the engine is warm and solved the problem, please let me know. I'm somewhat perplexed by this.
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Triangles
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Re: Left cylinder stops firing after engine is warmed up.

Postby Triangles » Tue May 16, 2017 11:52 pm

So it appears I have a bad left plug boot. Apparently the dielectric grease I put in the plug boot years ago didn't make it up to the brass piece that clips on the spark plug. it corroded and no longer "clips" onto the plug wire. I'm not sure why it would work when cold then fail when warmed up but it does.

So the fix is going to replace the plug boot and possibly the plug wire. I measured the resistor in the plug boot and it was exactly 5.00k Ohms. I did some googling and came up with this NKG XD05F 5k Ohm resistor spark plug boot which looks like it might just be a drop in replacement for the OEM spark plug boot! I also got a crash course in plug wire technology. Hopefully someone will chime in who knows more and can tell me if I'm on the right track or not. It appears there are 3 plug wire types; 1) carbon core(conductor) which are high resistance, 2) spiral or MAG core which are lower resistance, and 3) metallic core. OEM is metallic core which offers the least resistance and practically no RF/EMI suppression. This can cause problems with electronics or electronic engine management. However I think the 5k Ohm resistor magically suppresses the RF/EMI??? The carbon wires offer the best RF/EMI suppression but probably aren't suitable for use on our bikes due to high resistance. Someday I still plan to try to fuel inject my motorcycle so I may try using the spiral/MAG core wires but I'm not sure if that means I can delete the 5k Ohm resistors or not?
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Triangles
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Re: Left cylinder stops firing after engine is warmed up.

Postby Triangles » Thu May 18, 2017 8:38 am

Well I got impatient. Plus I needed some plug wires for my '89 Honda project so I ran out to Advance Auto Parts and got an Accel 5040R V8 universal plug wiring kit. It has a spiral wound core with 500 ohm resistance per foot. Seeing as how the plug cap had a 5k ohm resistor I was slightly concerned about essentially removing the resistor. To my knowledge the resistor's only purpose is the suppress RF generated from the coil pulse. I figured the spiral wrapped core should do this and we don't really have much in the way of electronics on the EN500 to worry about RF interference. The big question was whether or not the ignition system was designed to need the resistors. I replaced the bad plug cap/wire with a wire from the kit. Apparently the ignition system does not require the resistors or the resistors also built into the spark plugs are enough to keep the magic smoke inside the ignition system. Either way I'm happily rolling again. If I had to do this over again I would not recommend doing what I did because the kit I bough had 8mm wire and stripping it to fit into the coil resulted in something too small.

So in a pinch you can use something like this to get you home but it's probably best to just buy a new spark plug cap. Further as I went down this rabbit hole I've learned that our OEM spark plug wires are just copper wires and should never need replacing unless they become physically damaged. It's the carbon/fiberglass conductor car wires that wear out and need replacing which wouldn't work on our bikes anyway. Also I should have saved some money and bought something like this Accel 3008 universal wire kit. The kit is 7mm so it would fit into the coils. You're still eliminating the resistor from plug cap which I'm still not sure if that is a good, bad, or indifferent thing.
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Triangles
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Re: Left cylinder stops firing after engine is warmed up.

Postby Triangles » Wed May 24, 2017 1:55 pm

well I replaced both spark plug boots reusing the OEM wire. As you can see the new NGK boot is about 4-5mm shorter than the OEM.
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here's the guts of the boot showing the 5K resistor. I already tossed the failed corroded OEM one before thinking of taking a picture.
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I used generous amounts of dielectric grease at all connections to prevent corrosion. put everything back together and my one concern is that with the new NGK boots being shorter the rubber boot to the sparkplug wire is pretty much resting on the valve cover. If I were doing this again I'd buy the straight ones as I think there is enough clearance except maybe the fuel petcock vacuum hose to use the straight up. I also forgot to take a picture of the automotive plug wire/boot that I used temporarily. Needless to say I have no faith in the automotive plug wire/boot being anything other than a temporary limp home repair.
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I put the gas tank back on and she fired right up. I also turned the lights out and verified no sparks were jumping from the boot/wire where they shouldn't be.
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