Vintage Dirt Bike Q & A

Ok, not really elsinore but i figured i would post up anyway. One of my race bikes is an SL100. Yesterday i was doing a scramble with it and the plug boot came off the end of the wire. The last half inch or so of the plug wire is kinda sloppy. I am not sure i can just keep on screwing a new plug boot into the old wire, and i dont have much room to shorten the wire either. What is the standard in replacement plug boots for bikes?

Replace the wire and cap with after-market NGK product. Easy to spot - it is bright red. Get it from any good motorcycle dealer. Use a little silicone to get a water-tight fit at the coil end.

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Michael Stiles
1979 Honda CR250R Elsinore | 2006 Husqvarna SM510R | 2007 Service Honda CR500R-AF

i think all of my bike coils have the plug wire molded into them? I didnt think you could replace the wire

Here's a link to the NGK plug cap line:

http://www.ngksparkplugs.com/docs/Resistor_Covers.pdf

I got a bunch of different types of these to try out, and ended up using the LZFH as it was compact and non-resistor (any of the 1k units would have been fine too). You have to remove the threaded screw terminal from the plug for the LZFH to work, but it then snaps on the plug threads with the grip of death.

At the bottom of the .pdf document is a female-to-female inline coupling that allows extending the coil wire; this may come in handy too.

It's important that the coil wire strands be tightly compressed together and in good shape (clean, not oxidized, etc.), and that the plug cap be twisted squarely onto the plug wire. The cap has a central pointed screw that must burrow into the center of the plug wire strands; don't screw it on too far or it will "strip" and the cap will feel loose (it may still work OK, though).

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric

excellent info as usual ray. More questions though. Why can i only run the 0 ohm or 1k ohm resistor boots? what is the side affect of the 5k or 10k models? I think some of the longer 5k ones would be the ticket but i do not want to affect performance.

Well, as you know, the only reason the resistor is there is to cut down on radio interference. It may stretch out the spark a tiny bit, but it will always reduce its intensity.

My baseline setup was the LZFH non-resistor cap and my current favorite plug (NGK BP7EVX, non-resistor, Yamaha P/N NGK-BP7EV-X0-00). This arrangement had the best low end power and throttle response, and the steadiest idle. The BP7ES is the standard version of this plug.

I also tried the LB01EP 1k ohm cap with an NGK BPR7EIX 4.5k ohm resistor plug. Idle and low end weren't quite as good, but everything else seemed fine. I also got TB05EMA and YB05FP caps, but didn't test them.

I'm not talking huge differences here. I think you'd be hard pressed to tell the difference between a non-resistor and 1k ohm cap when using a non-resistor plug. That being said... these vintage ignition setups don't really have excess spark power to burn - especially at low revs - and I'd rather put what energy they have in the gap, rather than in the cap.

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric