Spark plugs, Which ones?

buzzstpoint

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Probably opening a can of nasty worms here. But, whats everyone like for plugs?
THis would be for my 81 xs400.

Typically I have always stayed with the type of plug the manufacturer recommended or style of plug from around that year(s) of engine.

But this was with cars and trucks. I know little about motorcycles. When I got the bike I changed the plugs, but put in what was in the bike. Now that I am sticking money into the bike, and wanting it to run nice. I was wondering about tune up and plugs.
I've replaced the wires and boots already.

At the auto store I work at, Oreilly Auto, some people have been putting in E3 plugs. Haven't heard any stories on putting them into bikes, But seems people like them for V8 Chevs (Newer models) and lawn equip.

Anyone use E3's in these older bikes?
 
to me, honestly, a spark is a spark and a plug is a plug. If your bike is running properly and it's tuned to near perfection, there is very little wear on spark plugs to begin with. When restoring my 50cc two-stroke from 1972 a few years ago, I pulled what looked like the original plug from 35 years before. It looked extremely old, the business end of it had become tiny and thin over the years, but it still sparked perfectly after all those years. I rode around on it for a few weeks before replacing it as a precautionary measure, but I could have probably gotten a few more years out of it.

Basically, it's an easy part to replace and sometimes they do fail. But 95% of the time the cause is something else than the plug itself, therefore I don't see any benefit for fancy plugs. If you've sorted everything else out, I strongly believe a $2 plug can take you to the end of the world and back.
 
If you want to upgrade your plug use the NGK bpr7EIX iridium ones. You can get them at napa for around $9 each. If you do use them make sure to change the caps to non-resistor ones as this is a resistor plug. I would avoid E3 plugs in the xs400 as they don't have a plug made for it. I found a set that was close to the stock number but after 100 or so miles the plugs electrodes started to melt and run very hot.
 
After going to several parts stores I've found that all their programs and books say to use the legacy plug BP7ES, which most placing a surprisingly for carry. They've all upgraded to the BPR7ES. They have lots of those, but the real hard part (for me anyways) was finding the non-resistor caps. And no one seemed to have heard about not pairing resistor caps with resistor plugs.
 
+1 on the ngk BP7ES. If you want your plugs to do more to beef up your bike, fine tune your stock carb or look into carb modifications that would give more fuel to the spark throughout the various throttle positions. Stock plugs are what you want to tune around anyway, properly gapped and inspected during fine tuning will last decades. Never heard of resistor plugs bit I do remember testing my plug wire resistance at some point.
 
This is what to expect using them. The exact numbers are different for the xs400 but the percentages should be close.
 

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There are large differences in spark plugs. Here is what I've learned:

Champion plugs will get your bike to run, and may mask minor carb jetting or ignition issues.
NGK plugs will last longer, but are finicky and susceptible to flooding. They will never work right after being soaked with fuel.
NGK Iridium plugs will last the longest and perform better due to their design, as shown in the dyno chart Chris posted.

I'm currently running NGK Iridium plugs with resistor caps and not having any problems. I plan on trying non-resistor caps (later on) to see if they make any difference.

Some may argue that as long as the spark ignites the mixture, that is all that matters. Well, let me tell you that there is a big difference between doing a job, and doing it well. Flame front propagation is very important to proper combustion. Conventional spark plug design can shield the spark and flame kernel from the combustion chamber. The fine center electrode of the Iridium plugs, and the tapered ground electrode, both allow for greater exposure of the flame kernel to the combustion chamber and the mixture. This promotes smoother combustion, which results in more power and better economy. This is one of those times where you can have your cake, and eat it too. If you are willing to spend a little more up front.

Just remember, every misfire is over a 50% reduction in power. Probably close to 70% once pumping losses are factored in. Poor or incomplete combustion will quietly rob you of performance and economy with every combustion cycle.
 
interesting stuff guys, I didn't know this :)

actually makes me consider getting iridium next time, sounds like a pretty easy and sound investment
 
I put the ngk iridium plugs in my car mostly for longevity. I think the performance gains you get are probably from a more accurate spark with fewer misses. It's not something you'll feel, but you may be able to measure it if you're tracking fuel consumption.
 
I just buy the cheap ngk plugs, but when I owned 150cc scooters I ran the iridium plugs, I noticed much smoother idle but that's in a cheap Chinese scooter,
 
Reviving to clarify iridium versus standard NGK plugs question.

My non-running bike came with iridium s improperly gapped to about .95mm. I assume iridium still should be gapped the same .

I'm assuming they didn't know or bother to change the caps to non resistor type, but unsure how to check this. Can anyone advise how exactly to confirm? Google has not been revelatory...
 
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Didn't realize they were threaded terminal stud. Poor Prior owner bought these plugs to try to get bike to work and don't think he ever put 5 miles on them
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Plug gap should be between .028-.032in I run .030 with my iridium plugs. With the better spark you could run them a bit more open but I haven't done any testing of this. There are threads on the xs650 forum on this subject.
 
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The caps will have a resistance value or model # on them if they are NGKs.
Can lookup the resistance spec in their catalogue.

Or use a multimeter to check resistance. The cap will untwist from the plug cables to put a test lead in both ends.
 
NGK boots will have a stamp on them. Itll say something like Ω5k, which means 5000 ohms.

Ive run both the stock plugs in multiple heat ranges, and irridium on both electronic and points ignitions.

The irridum plus helped the bike to idle smoother, but the bike had a weak rev. It made the bike sound gutless. Maybe it was just running more efficient and that cleaned it up a bit?

The traditional plugs gave the bike a bit more bark in the rev and revved faster than irridium.

Tuning was easier on the regular plugs too.
 
Thanks lads! Plug wires just say made in Japan on them so I assume NGK but will verify. They have an outer layer of rubber on them that is cracked and pretty worthless looking. Assume for a couple bucks I'll just replace them eventually. Haven't checked anything inside coils but did confirm both plugs have spark.

I'll keep the set of iridium and regular to compare when tuning
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