View original topic: Super weird spark plug issue
Fritzer108 Fri Aug 28, 2020 11:20 pm

Spoiler....this is for a vintage Honda but I hope your expertise can still help me out of this mess. I do own a Type 1 so I am not a complete degenerate. The bike (yes a motorcycle) is a 1974 CL360. I replaced the plugs and have power coming out of both caps. The left cylinder works fine but once I screw and tighten the plug on the right, my right cylinder does not fire. If I take it out and hold it against the head, all is fine. This leads me to believe that I don't have a good contact between the head and the plug, which I find rather interesting. These are brand new plugs.....i bought them today and have put 0 miles on them.

Retrovan Sat Aug 29, 2020 7:26 am

Put a jumper lead from the head to the body and see if it then works.

You could have a faulty plug that on fitting gives an open or short circuit.


Fritzer108 Sat Aug 29, 2020 8:25 am

Just to clarify, I know that they don't spark when I screw them in because 1, after about 10 minutes of running, the right exhaust is stone cold and 2, if I remove the right spark plug cap, if has no impact on the engine.

DeathBySnuSnu Sat Aug 29, 2020 7:07 pm

Basically the same troubleshooting as the dub.

It could be a weird plug issue....but likely not.

If it sparkles when out.....then check the tappets....if that ain't it then go in the carb.

VOLKSWAGNUT Sun Aug 30, 2020 11:18 am

Suck bang blow.. .. takes air, vacuum, fuel, compression, timing and exhaust.. missing one of those.. an engine wont run

Just because that cylinder is cold.. doesn't mean its spark.

If you know 100% its getting fuel to that cylinder and compression is good.. and.. there is no intake or exhaust restrictions..... and you thinks its a spark issue.... .then...

High resistance in the plug wire or screw on spark plug boot/cap.
The plug boots have built in resistance.. and.. after years.. they fail increasing resistance.

I just replaced my coils and boots on my 750 four (K5) . Number 4 plug was intermittent and had almost the exact same symptoms.

Buy original NGK's ..

Try this.... place the #2 boot/cap lightly on plug and with the engine running.. slowly start to remove it.. you should hear the spark snapping at the plug tip.. if it starts to fire that cylinder.. get the NGK caps.. and be sure the plug is clean and gaped correctly..

Its harder to fire a plug under compression pressure. What may spark out of the engine.. may be basically blown out under compression.


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