Cracked Spark Plug Cap

[Tortuga]

Would a cracked (several pieces) spark plug cap make bike ('06 Nomad) idle rough and show some surge or hesitation? Good acceleration, starts well. Hard to tell if surge is at speed due to blustery winds, but do notice it at slow speeds and in parking lots, etc. Strangely, MPG have gone up substantially. Got 47 riding mostly with the wind (2 up) and 41 2 up against a very strong mostly head wind.

[andyvh1959]

Easy test of plug caps and wires; get the bike idling in the dark, no lights. Use a hand pump pump water bottle to spritz a water mist on and around the plug wires. If you see sparks from the wires or plug caps the insulation is failed and you are loosing spark to false grounds. NGK makes good replacement plug caps.

[Tortuga]

Thanks. Sure enough the plug with the crunched cap sparks when sprayed. None of the other caps or wires show any sparks. I ordered an NGK cap last night as I figured there was a reason it was there but your suggestion confirms my instinct. Now we'll see if replacing the cap solves the problem.

[mick56]

There is a hell of a lot of bad NGK stuff coming out of China. I went through 8 plugs, to find 2 good ones recently. My local parts shop, wont even stock them anymore. I switched to using Champion plugs.

[andyvh1959]

Thanks Nick56. I wasn't aware of issues with NGK spark plugs. I have replaced plug caps on many Honda and Yamaha bikes I've worked on and all gave me great results. Can't say I've ever had an issue with any NGK spark plug.

I'm curious, how did you confirm two of eight NGK plugs were good? Just by connecting each one to the coil lead and checking for spark? I have found more issues with plug caps than plugs. Old, OEM Honda and Yamaha spark plug caps can eventually develop high enough resistance to cause a spark failure when submitted to compression in the engine. For example, I have tested for spark on an OEM coil, coil wire, spark plug cap and got a weak yellow spark, and the bike would not run. Then replaced the plug cap, and on the same coil and coil wire got a bright violet blue spark, the bike fired right up.

[mick56]

Originally Posted by andyvh1959

Thanks Nick56. I wasn't aware of issues with NGK spark plugs. I have replaced plug caps on many Honda and Yamaha bikes I've worked on and all gave me great results. Can't say I've ever had an issue with any NGK spark plug.

I'm curious, how did you confirm two of eight NGK plugs were good? Just by connecting each one to the coil lead and checking for spark? I have found more issues with plug caps than plugs. Old, OEM Honda and Yamaha spark plug caps can eventually develop high enough resistance to cause a spark failure when submitted to compression in the engine. For example, I have tested for spark on an OEM coil, coil wire, spark plug cap and got a weak yellow spark, and the bike would not run. Then replaced the plug cap, and on the same coil and coil wire got a bright violet blue spark, the bike fired right up.

After trying 4 plugs, from ebay, all with weak sparks. I fitted new leads, and caps. Thinking they might be the problem. They were not. So i bought 4 more plugs, from a main dealer, and only 2 gave a good spark. So i bought 4 Champions, and put the old leads & caps back on. All was good then. Counterfeit NGK's, are getting into everyones supply chain over here in England. I wont ever buy another one.

[Tortuga]

Off with the broken cap, on with the new, off with surge/hesitation/rough idle, on with smooth idle/smooth acceleration. There's still a jerk on the throttle, but unless I sell the bike I'll always be the jerk on the throttle. There's no fixing that.