• Ok this is strange. The other day on the way home my bike started running rough

    Ok this is strange. The other day on the way home my bike started running rough. Got home and found it was only running on one cylinder. The left exhaust was really hot and the right exhaust was warm to touch.

    I re checked everything Had spark on both plugs, the condenser was good I reset the points to be exact and still running rough. Grab the timing light and hooked up left side and the timing light came on and timing was right on... hooked up the right cylinder and the timing light would not come on...

    Not knowing what to do I took off and rechecked the right spark plug and there was spark. But then I decided to put an older plug and sure enough the timing light worked and the bike fired up and ran like normal.

    So to double check I put the right plug on to the left side and there was spark put no timing light. Definitely a bad plug that looked normal and did spark but not good enough for the bike.

    Moral of this story is that plugs may not necessarily be good even though they spark.

    Anyone had this experience??

    16 comments
    • If you use the above mentioned plug, you will have to replace your caps with non-resistor caps. Unless of course you already have non-resistor caps. In which case, carry on.

    • Today's plugs( especially NGK in my experience) seem to go bad real quick & sometimes will show a healthy spark until under compression.

    • sure pissed me off having to ride back the way it was oh well those eix sound good.

    • What do you mean not true? The resistor plugs already HAVE an onboard resistor!! Why would you want to run a second resistor with them? Not saying it's impossible, but your spark won't be as hot or as effective. That's simple electricity 101 man...

    • I would just ask you to look into use of iridium (resistor) plugs with a resistor cap before proceeding, though I am being told I am wrong on this issue...

    • It's not about the amount of resistance BEFORE the plug fires. The energy from the coil is dispersed more slowly from the coil after the spark jumps the gap whenever more resistance is added to the line. So once again, it creates a weaker and longer spark.

    • But as it is your bike, please continue to run what you like :) I will do the same here.

    • EDGAR....... Are you using .035 gap as an example

    • I have been racing with the same 20 NGK plugs for 22 years. only cleaning and replacing ones if the electrode has started to melt or distort under extreme heat, never had one stop working.

    • nope. it's not.

    • I am now really wondering if I may have the wrong plugs and cap. The cap is a NGK YB05FP 5KOHMS the plug is NKG B8ES with air gap of .030 . Is anyone else using this combination on thier bikes.

    • Iridum has a hardness that is twice that of zink used to coat plugs which seems to me it wouldnt matter which one was used . I do know plug companys will dream up all kinds of ideas to sell plugs when the fact is they all are designed to do the same thing and work under the same conditions I run as high as 13 to 1 ratios in these motors and have never had a reason to change the standard plug Ive been racing with for 22 years...These are just the racing hi-temp hi-pressure results I delt with over these years.

    • I've had a plug that would spark ok but wouldn't under compression. I will be using whatever the manual says when I finish my engine. I will try no improvements until I get it running properly std.

    • Have you tried bosch plugs,yet?

    • what number have you used..

    • Under compression the only reason a plug wont fire is lack of voltage the plug is just the grounding point. so long as its not damaged or broken in some way. Has anyone used NGK fine wire EV plugs. They require less energy to fire. I use these in motors with very high compression with very good results.