I have already repl.plugs 2 times in less than 3500 miles.Idle seemed to drop a couple hundred r.p.m.'s when eng.temp full hot.When plugs were pulled they were somewhat fouled(black),but not wet or excessive discolored or caked w/ soot.I don't have a problem with it except gas mileage is low 40's generally.Ceramic was brown but steel in the cylinder was black.I'm wondering if I could benefit from a dyno and computer tweeking.And where or whom would do it,and where would I get the proper air /fuel ratios from ,published.The bike was used when I bought it but seemed well cared for for the most part,as prior owner had oil ch.reciepts from dealer,and stock replacement parts on it.

You shouldn't have to changed your plugs that quick so maybe go talk to a mechanic about this. Do you have the gaps set properly? And also, when you say you get in the low 40's, what kind of driving is this. If you are on the interstate doing 80 mph indicated or more that is about right. It is also cold in Illinois and the cold will lower your mileage too. I am seeing that my mileage is about 4-5 mpg lower, but then California uses a very clean blend for their winter gas out here.

I'm also not sure if you can dyno a SWing without getting a power commander for it. Maybe others can chime in. I now that Bernardo and Honda-silver has those installed so maybe they know.

I have only changed my plugs 3 times and have 13,000 miles on it. Doesn't sound right to me. either.

Odd indeed. I see that you live in Illinois so undoubtedly you are getting an ethanol blended gasoline. That along with some slightly cool air temps will result in lower mpg. JeffR is spot on regarding the speed, higher sustained speeds are not SilverWing mpg friendly. It really sucks down the fuel at interstate speeds and much more so when the air temps are cold.

Honda recommends plug replacement at an 8,000 mile interval for the SilverWing. Be certain that whatever plug you use as a replacement falls into the correct temperature range for the SilverWing. Compare the temperature range of the OEM or Honda recommended plug with the temperature range of your selected replacement. This may be a cause for some disappointing mileage figures.

I agree, It sounds like your scooter is running very rich. I have almost 23,000 on mine and change every 8k like the book says. The plugs look good each time i replaced them. I also keep my old plugs and mark on the box the date and mileage when i changed them. This way i can get an idea of the running condition of the engine over time.
Paul

duanne,

One other thing, what are you gapping your plugs at? When I changed my plugs one was only at .26 and the other was the proper gap. I believe the proper gap is .031 to .035 . But I will check it out again and get back with you. Hope this helps some but I'm sure you have tried many things to figure this out.

Bill,

This will be unfortunately a fairly long post...

The OEM plugs:
NGK - CR8EH-9 (3rd digit is the heat range number
NGK web site showing codes: http://www.kaila.net/tl125/tl125ngkcode.html
DENSO - U24FER9 (check this: http://www.factorypro.com/Prod_Pages/prodh27.html)

I typically don't deviate away from the OEM plug - as the result of some observations I made while working as a service advisor at an Acura dealership. At that time the platinum spark plug was all the rage and we had several customers who changed out the OEM pugs for "the next great thing" as the platinum plugs were thought to be. We (at the dealership) had a rash of customers coming in and reporting poor idling, poor acceleration (stumbling & pinging), poor mpg, engine run on, etc. They assumed there was something wrong with the engine as they had just "upgraded" to the platinum plug. There even were some Technical Bulletins from Honda/Acura to describe the problem - the recommended solution as you'd expect was to reintroduce OEM plugs. This is not to say that aftermarket plugs are bad, just to remind folks that there's more to it than just pulling and replacing the plug. I'd think that the advantage of an Iridium plug is longevity, just stick with the proper heat range. the text string I typed into the web search line = "spark plug heat range codes", vary this some by typing the manufacturer name before the rest of the text eg. = "NGK spark plug heat range codes"

Bosch description of Heat Range was succinct:
The spark plugs’ heat range is an index of its capacity to dissipate thermal energy. The different characteristics of automotive engines regarding operating load, compression, engine speed, cooling, and fuel make it impossible to run all engines with a standard spark plug. The same spark plug may get very hot in one engine type, but may reach only a relatively low temperature in another. In the first case, the air-fuel mixture would ignite on the glowing parts of the spark plug projecting into the combustion chamber (pre-ignition) and, in the second case, the insulator tip would soon become so badly fouled by combustion deposits that misfiring would occur. To ensure that the plug runs between the desired temperatures, plugs with different heat capacities were developed. The so called “heat range”, which is assigned to each spark plug, is used to characterize these heat dissipation capacities. A plug with a low heat range number (e.g., 2-4) indicates a cold plug that quickly dissipates heat to the engine block and cooling system, while a high code (e.g., 7-10) indicates a hot plug that retains heat. By properly selecting the heat range of the plug, it ensures that the plug will operate between the plug’s designed operating range of 500-900 degrees Celsius. In this range, the spark plug will be self-cleaning, yet will not be hot enough to pre-ignite the air/fuel mixture.

Any help or just more confusion?

Dale,

Even though I'm not a mechanic what you said makes sense. I changed to an iridium plug for a couple of reasons:

a) I just wanted to see what if would do different, if anything and
b) It was about time for me to change plugs anyway

I thought it made a difference since my SWing seemed to run smoother and idle better. But after I posted that it seemed smoother others started asking me questions. After so many questions I went out and checked the gaps on the old ones. 1 plug was right on the gap of the other plug was only .0026. So maybe that is why the SWing seemed to idle and run smoother.

I am going to pull them out and check them to see how they look. I have had them in for about 12,000 miles now. I will take some pics and post them and also check the gap.

Great point Jeff - Thanks for pointing out that checking/setting the correct gap is probably the one other element, besides heat range that really makes a difference. The gap on SilverWing plugs per the service manual is 0.031 - 0.035 inch. Or, for our metric friends - 0.80 - 0.90 mm.

Remember - The measuring tool should make full contact on both sides there should be slight resistance, but it should not be difficult to pull through the gap.

Replaced my plugs a couple of hours ago. I stuck with the standard plug. One note on the pictoral guide (which is great), it states that the torque on the spark plug on JeffR's 2007 is 16ft lbs. After tightening by feel with a 3/8" drive ratchet (which is how I normally do it anyway because you can't get a torque wrench on the spark plugs on a lot of bikes) I decided to check with a torque wrench. While checking I felt that I was applying more torque than should be required. At least more than my feel was used to so I stopped and checked the shop manual and under General Information my 2002-2007 manual states 02-04 is 9 ft lbs and after 04 it's 12 ft lbs. It does say that after 04 the torque should be 16 N.m. If I have this somehow wrong or it has previously been addressed please accept my apology. I think the moral of this story is we should always refer to the manual for the correct year of our scoots. JeffR has done us all a great service by providing these how to's with pictures along with Dennis and others. Thanks to all. Dick

Dick,

I'm glad the Pictorial worked for you. Thanks for pointing out the torque for the plugs. I will look at the manual again and I hope no one had problems if they torqued it too much. It's kind of strange that their are different torques since the SWing hasn't really changed that much, as for as I know. Thanks for the update Dick, and if you find more please tell me.

Frankly I hadn't looked in the manual to see when plug replacement is called out. 8000 miles seems pretty often. I ran about 80,000 miles on a set in my GL1500 and didn't see any change in starting, running or mileage when I recently replaced them with the OEM plugs.
A little soot in the plugs as duanne discovered could easily be due to dirty injectors, out of sync throttle body or a defective MAP sensor among others. One thing I find does a great job as a preventive measure on my SW, GW, F250 and Mercury Milan is a shot of Sea Foam a couple times a year. Here on the West coast all pump gas has 10% ethanol, it seems to make my bike run smoother after a tank treated with Sea Foam. The stuff helps to keep the injectors clean. I don't normally recommend 'miracle-in-a-can" but this stuff is good. It's available at most auto parts stores and Wally World as well.

As an aside, I have a sneaking feeling Honda do make modifications but keep it a secret - I read with interest about fitting different shocks on the front because of excessive dive under braking but I'm sure my '09 model doesn't, at least it doesn't appear so to me. Perhaps the shocks have been uprated from the factory.