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Discussion Starter #1
Is it a platinum, and does it really need to be replaced at 10k?
 

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Discussion Starter #3 (Edited)
Was that the original? Or replacement ? Most plats and iridium are good for 100k on a car , probably 50k on the one holed lunker!
 

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Just realized I've Got 18k on my current plug. I think I'll change it. Runs great though.
 

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The service schedule is totally BS. On a old style resistor plug the schedule was about 20,000 miles. I'd say at 10K, check the gap and reinstall.
 

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Ok, so many of you know this but worth repeating for those that are not sure. There are some plugs that can go more miles than the service schedule mileage recommended in the handbook and still be efficient. But if you are using a standard NGK (oem) or equivalent, then best practice is to change it somewhere near the recommended mileage. 7,500 is the recommended miles on the 400 399cc engine, but it's ok to go to 10k in my book without loss of efficiency. It is not the way the electrode looks that tells you how good the plug is, whether it's worn or not etc. The key point to know is the more miles a spark plug covers, the higher the firing resistance so the more voltage is needed to spark the plug. If it can't get more volts (which it cannot) it has a reduced spark performance. So less performance, less mpg, less efficiency and more likelihood of failure which in it's self is rare these days. It's such a gradual change we don't notice it, especially if our bikes are newish and still lowish miles. The reduced spark plug performance is often missed because the engine mechanicals loosen more and the engines natural power increase is still happening well on the way to 20k. The plugs lose efficiency because the internal plug insulation breaks down gradually. We tested a range of plugs a couple of years ago for our new engine which at the time was under development. We settled on a good oem plug and ascertained the correct service interval for a change. Several plug companies were helpful on this. It was a high compression engine (11.5 to 1) so the spark plug becomes less efficient sooner in an engine like that. Our 400's with the 399cc engine are 11.2 to one unless a Canadian model. We found at 20,000 miles the spark plug resistance was more than double what is was when new. That causes your coils and HT electronics to run hotter. Not good for you bike or car. The engine was producing less power too. Plug changed and an instant boost came about. If using an irridium or a brisk plug, then you can go longer.
 

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Ok, so many of you know this but worth repeating for those that are not sure. There are some plugs that can go more miles than the service schedule mileage recommended in the handbook and still be efficient. But if you are using a standard NGK (oem) or equivalent, then best practice is to change it somewhere near the recommended mileage. 7,500 is the recommended miles on the 400 399cc engine, but it's ok to go to 10k in my book without loss of efficiency. It is not the way the electrode looks that tells you how good the plug is, whether it's worn or not etc. The key point to know is the more miles a spark plug covers, the higher the firing resistance so the more voltage is needed to spark the plug. If it can't get more volts (which it cannot) it has a reduced spark performance. So less performance, less mpg, less efficiency and more likelihood of failure which in it's self is rare these days. It's such a gradual change we don't notice it, especially if our bikes are newish and still lowish miles. The reduced spark plug performance is often missed because the engine mechanicals loosen more and the engines natural power increase is still happening well on the way to 20k. The plugs lose efficiency because the internal plug insulation breaks down gradually. We tested a range of plugs a couple of years ago for our new engine which at the time was under development. We settled on a good oem plug and ascertained the correct service interval for a change. Several plug companies were helpful on this. It was a high compression engine (11.5 to 1) so the spark plug becomes less efficient sooner in an engine like that. Our 400's with the 399cc engine are 11.2 to one unless a Canadian model. We found at 20,000 miles the spark plug resistance was more than double what is was when new. That causes your coils and HT electronics to run hotter. Not good for you bike or car. The engine was producing less power too. Plug changed and an instant boost came about. If using an irridium or a brisk plug, then you can go longer.
+1.
 

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I've never run anything but the standard OEM NGK plugs in my 650. I change them when I check the valves at about 25,000 mile intervals. Never seem to have caused me any problems. Fuel mileage has remained constant. Performance has remained constant. No hard starting. etc etc.
 

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Went 37,500 on my 400 before changing. Once changed I saw no difference. Plugs now a days will last way longer than they use to. We went about 75k on plugs in police cars at the city I was fleet manager for. ;)
 

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Don't forget car engines are much easier on the spark plugs. Lower compression, and lower revs. Most car engines run a cooler burn and run higher volt HT systems. Our 400's run at an average 2.5 times the revs of the average car for any mile driven so they take a hammering. Buffalo, you are losing some efficiency if your plugs have covered 25k. However your ECU via the closed loop is compensating for the smaller spark so in normal riding you may not notice it much. But open the taps wide and let it rev out and you will see more of a difference as the ECU cannot keep the burn in normal parameters. Put it on a dyno and its very evident, you would see it. For what they cost new plugs are worth it in my book.
 

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Went 37,500 on my 400 before changing. Once changed I saw no difference. Plugs now a days will last way longer than they use to. We went about 75k on plugs in police cars at the city I was fleet manager for. ;)
Well a little 400 thumper is a lot different than a V-8 police car or even MC, but point well taken. The spark plugs today seem to last way longer than they used to.

I've gotten 18k out of my current one, for a $5 part, its worth replacing.
 

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Buffalo, you are losing some efficiency if your plugs have covered 25k. However your ECU via the closed loop is compensating for the smaller spark so in normal riding you may not notice it much. But open the taps wide and let it rev out and you will see more of a difference as the ECU cannot keep the burn in normal parameters. Put it on a dyno and its very evident, you would see it. For what they cost new plugs are worth it in my book.
Might show up on a real dyno but it doesn't on my seat of the pants dyno which is the one that matters. Doesn't seem to accelerate any faster with new plugs than it did with the old ones. If I can't tell the difference and mileage is the same then it's not worth worrying about. Changing them when I check the valves is convenient because I have the radiator off and it gives good access. Besides I have to pull them anyway to remove the valve cover.
 

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Discussion Starter #13 (Edited)
I don't plan on pulling this thing apart either just to check anything. If it was a 15 minute job yes, but To tear this thing down just to check the "valve clearances" and redo the gasket every 10k heeeeeeeell no, I'm going to ride her out for a 100k boys before I undress her! Lol
 

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I guess I'm middle of the road on the maintenance issue. Sure I replace the belt, clutch, and brakes when they need em. Spark plug too and I just ordered a new air filter. But at some point, I don't have the facilities, talent or inclination to keep the old girl in perfect shape. I've already gotten my money's worth and probably have as many miles to go on her than have passed.

Given shop and parts rates vs. the prices of good used bikes, I'll run her till she dies and then find a new love.

But having a second bike helps spread the miles out and elevates the urgency should something break. I'm very lucky.
 

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When I had some down time at about 27,000 miles due to my health, I changed out my OEM plugs with the Iridium ones from my 03 650, they had 25,000 on them at the time. I did notice it ran a bit different. But then I remembered that we went to summer gas at that week I had gassed up and I had put in some Seafoam in the gas too. So my test was tainted. ;)
 

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I had between 35k and 40k on the plugs on my Concours when I replaced them. I figured it was a good idea while I was in there, but it's not as if there were any problems. But once I got in there I was startled to see that the little metal arm where the spark jumps the gap - that little arm was about the thickness of a sheet of paper. Glad I replaced them before one broke off and fell down into the cylinder.
 

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Discussion Starter #17 (Edited)
I'll do mine every summer as it it seems quite easy to do by all accounts, i'm not one to avoid any type of maintenance...The only reason i mentioned the valve clearances is because from what i have read, almost everybody who checks them never have to do any adjustments...

What one guy said was great info though, and that was the valve seat wears before valve tip creating a smaller clearance for the valve, but i think he said at 100k he had a slight drag on the valve which of course creates a hot valve and burns the valve up as it cannot cool against the head. I just think checking them every 10k is rediculous, but i'm sure that keeps suzuki out of hot water should there be some clearance wear that does not show up on their factory test's. I might pull the cover at 50-75k lol
 

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Checking and changing the spark plug is a 10 minute job on the 399cc K7's onwards. Just one little panel to unclick just below the front of the seat. Checking valves you will also find very easy on these 400's. It's every 14,500 miles though, not 10k. If you are one of the unlucky ones that needs to adjust one or more of them, then that too is simple if you have a torque wrench and read the workshop manual first. No problem for most people. As long as you don't ignore them, that's the secret. One in ten bikes needs the valves adjusting at the first valve inspection on average (source: our workshop).

Buffalo, agree with your mindset in your particular case. You know what you are doing and whether a plug is looking dangerous.
 

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I changed my plug today for the first time! Yea! And you're right Quantum, it was an easy job. I shall do it more fastidiously from now on.

However, as to the question on real world milage, this plug has AT LEAST 18k on it and may even be the original one. I don't know, it took the bike in once for a major service at 17k. Dealer may have replaced it then. But in either case it doesn't look too bad. It was still in gap spec, .8mm and I didn't notice much, if any performance improvement. (I did the air filter also).

View attachment 19561

Moral of my story... Change your plug, its easy and cheap. You can do it with the tools that come with the bike and there are instructional videos on YouTube.

https://m.youtube.com/watch?v=3BjyR_rZZRg

But don't worry yourself if you're a few thousand miles past due.
 
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