![]() The new spark plug boot tested right on par with the 5K ohm spec. That’s when I found that, instead of the stock 5,000 ohms, they both were reading significantly higher, closer to 8 kΩ.Ī new set of plug boots was ordered shortly thereafter. So to get the bike to run smoothly, I checked everything first, including the spark plug boots. (In fact, we saw this with an old blower motor resistor a little while ago.) In my experience, it often means the resistor will gradually increase its resistance, until it ultimately fails open and you get a complete break in continuity. (Image/OnAllCylinders)īut as anyone who works around old electronics already knows, resistors can drift off-spec with age. The other one wasn’t much better, coming in around 7.5 kΩ. Here’s one of the bike’s 50-year-old OE plug boots, measuring over 8 kΩ. No need to worry about using the wrong boot there. You just have to pick the right boot for the specific bike application (Image/OnAllCylinders)Įasy enough-while I was resurrecting the little Honda, I replaced the coils, but planned on merely swapping the old, original plug boots onto the new ignition wire ends. Unlike many automobile coils, a lot of vintage motorcycles run coils with the ignition wire already attached. In the case of the Honda, it required a right angle boot with 5K ohms of resistance. ![]() You simply add the correct spark plug boot for your motor’s application. Resistance In the Spark Plug Bootįor a lot of vintage motorcycle engines, the ignition coil has an integrated spark plug wire. ![]() Yet the spark plug thing was only part of the story. (The goal here was to return the bike to as close to showroom-spec as possible.) And since there’s no radio or ECU to worry about in a 50-year-old motorcycle, I simply cleaned and re-used the old, non-resistor NGK B8ES plugs I had in there originally. Problem is, that extra resistance can also affect things like spark duration and intensity-which for a small carbureted twin-cylinder engine that demands precision ignition timing, could potentially hinder the way it runs. More importantly, for vehicles that do have those high-tech electronic systems, they can be downright essential. Resistance-type spark plugs are quite common these days and for a large spectrum of engine applications, they’re perfectly fine. As expected, with a multimeter on the NGK BR8ES, it tested right around 5 kΩ. Resistance is measured in Ohms, represented by the “Ω” Omega symbol-just ask Charlton Heston. The job of that integrated resistor is to reduce electromagnetic interference (electrical noise) stemming from spark discharge that could impact electronic systems like a vehicle’s radio or, more importantly, its ECU. (Image/OnAlllCylinders)īut in the case of the NGK B8RES, the R means that it’s got a 5,000 Ohm (or 5 kiloohm/5 kΩ) resistor built in. We used some ultra-fine grit sandpaper to clear away the buildup here. To get good resistance readings (and optimal performance in general), it’s always a good idea to keep the plugs’ electrodes clean. (Two were also already in the bike when I began its restoration.) Nowadays though, that particular spark plug has been superseded by the NGK B R8ES. Figuring it was best to start fresh with new plugs, I dove into my ancient Honda shop manual, which said the bike requires NGK B8ES spark plugs-a very common plug at the time. It all started when trying to buy new spark plugs for that aforementioned CB. ![]() (Image/OnAllCylinders) Resistance Built-In to Modern Spark Plugs They’re virtually identical, save for the built-in resistance. Here’s a newer NGK B R8ES spark plug compared to an original B8ES. In the name of brevity, we’ll skip the electrical theory on the role resistance plays in an ignition system ( though Hemming’s has a great article on it here). There were some topics on spark that warranted a standalone article. Truth is, fuel was only part of the story. You may have read the earlier article on my star-crossed 1970 Honda CB350’s fuel delivery woes. While we’ve covered resistance in spark plug wires before, the opportunity recently arose to talk about resistance in spark plugs and plug boots too. Resistance values can play a role in your ignition system performance-and it all starts at the plug.
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