Spark Plug Gap Confusion

[Hueffenhardt]

The KYMCO Grand Dink/Vista Owner's Manual says the spark plug gap should be between 0.6 and 0.7mm. The Service manual for the KYMCO Grand Vista says the spark plug gap should be between 0.9 and 1.0mm. That is a big difference between what should be authoritative manuals from the manufacturer.

I set my new spark plug gap according to the Owner's Manual between 0.6 and 0.7mm and drove the scooter for a day. I found that the idle was a bit rough, and when I took the plug back out a little white deposit was starting to form on back of the spark plug "arm" (I don't know the technical term). I cleaned the deposit off, changed the gap to the service manual recommended specs between 0.9 and 1.0mm and put it back in. Today the idle has been much smoother, so I do believe the service manual was correct and the owner's manual incorrect in this case.

Oh, the old spark plug I was switching out had a gap just slightly smaller than the 0.9mm. It had what seemed to be a lot of black carbon deposit.

[Stig / Major Tom]

There is a sticker on my Kymco, somewhere- because there are a zillion hidden stickers on this thing - that gives the plug gap. I sorted this issue by just popping in the correct Iridium Denso....no gapping.

[zombie]

Gap effects timing to a micro degree. The tighter the gap the faster the firing, and the sooner the flame front hits the piston. Too soon is pre ignition, and rough idle is a symptom. The piston struggles to compress the expanding gases.
Bottom line on all spark plugs for all engines is 35 thousandths. Fail safe, and fool proof. .889mm

Don't trust the Denso gap... It may have gotten banged around during shipping/handling or just never set right to begin with. use ONLY a brass feeler gauge to set them at .035". Brass will not scratch off the plating. (that's why they say not to gap them) The plated tip is very fragile, and stainless gauges will take off the iridium coating.

Mass Iridium to all!

[Stig / Major Tom]

Don't trust the Denso gap...

Mass Iridium to all!

I've only handled 10 of these Iridiums (NGK & Denso) over the past 2 years - all come with end protectors - all were gapped perfectly.
I did have an old copper Bosche plug once that had been dropped in the box. I checked the first , then installed all of 'em. That was the day I owned a 3 cylinder Jetta!
Stig

[zombie]

You are right. It is RARE to have a bent electrode but I work on marine engines all day every day, and go thru hundreds of plugs every month. My odds therefore are almost off the chart.
It's just habit for me to gap them all at 35.

My keyring is one of those coin type gappers

[mrbios]

Every NGK I have ever used was gapped perfectly.  The gap changes the heat not speed.  The wider the gap the hotter the spark.  Electricity travels at close to the speed of light.  Either gap setting and the scooter should run and idle the exact same.  A white tip can indicate a lean burn.  What did the old plug look like?

The emissions decal / sticker on my scoot says 0.7mm.  However, it also says straight 30w oil and that is wrong.  I follow the manual and use 15w/40.

[mrbios]

Every NGK I have ever used was gapped perfectly.  The gap changes the heat not speed.  The wider the gap the hotter the spark.  Electricity travels at close to the speed of light.  Either gap setting and the scooter should run and idle the exact same.  A white tip can indicate a lean burn.  What did the old plug look like?

Update: 05-07-2014
The emissions decal / sticker on my scoot says 0.7mm.  However, it also says straight 30w oil and that is wrong.  I follow the manual and use 15w/40.

[zombie]

You are right MrBios. I sort of posted, and didn't think it thru... If the plug gap is too large the hotter spark will contribute to pre ignition, and if it is too small the colder spark may not completely ignite the charge
That's the beauty of a forum right there.

[mrbios]

You are right MrBios. I sort of posted, and didn't think it thru... If the plug gap is too large the hotter spark will contribute to pre ignition, and if it is too small the colder spark may not completely ignite the charge
That's the beauty of a forum right there.

No worries.  Your right forums are great.  I've been working on and reworking my carb cleaning & theory videos and I have made so many revisions where I catch errors in my voice overs - calling a part by the wrong name, stating info that turns out to be incorrect and so on...

Great article gives the thumbs up to using grease.

http://www.w8ji.com/dielectric_grease_vs_conductive_grease.htm

[zombie]

It is a long article but is still another opinion (like mine is).

This excerpt really takes both sides of the argument...

In regular low voltage multiple-pin circuit connectors, such as automotive applications, flooding with a proper insulating grease of low-viscosity dielectric grease is perfectly acceptable unless a manufacturer recommends against it. The grease should have good stability and not contain metals in any form, and be specifically designed for use as a dielectric grease. This generally is a silicone dielectric grease, although some Teflon based greases are acceptable.

In single low-voltage terminals or connections, such as metal-to-metal joints, grounds, or battery posts, almost any pure grease of light viscosity will be acceptable. Caution should be used with greases containing metallic powders to be sure any metal is compatible with the embedded grease metal. Connection enhancement from embedded metal powder is very minor, if it exists at all, and there is increased risk of bad connections if the metal powder has any interaction with the base metals.

I just clean, and tighten.
 

[Vivo]

and don't overtighten... especially on battery posts... they are soft...