Author Topic: plug gap  (Read 2340 times)

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jartist

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on: July 31, 2011, 06:51:36 am
I know spark plugs have been discussed plenty but bear with me here. I replaced my stock with an NGK BPR6ES and I felt at the time that the recommended gap felt a bit small at .028" (7mm). Has anyone just thrown in the NGK with the gap it came with? If I understand this thing correctly bigger gap is more voltage but too big risks over taxing the ECU?  The reason I'm asking is that my bike does the intermediate slow down at idle and some people reported that the NGK fixed it for them. I didn't really notice any difference in how the bike ran with the new plug.


Arizoni

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Reply #1 on: July 31, 2011, 07:09:19 am
On my new G5, the NGK plug did reduce the frequency of dying at idle and it did increase the idle speed a bit  but the computer seemed to keep on searching for the proper idle speed.

I reduced the idle speed because when riding in Phoenix the stop lights try to catch me forcing me to wait at the light.  When the temperature is over 105F, a  lot of idling can heat the engine up a lot.
I figured that if it was idling slower it wouldn't heat up as much.
I don't remember exactly what the mileage was but I know it was more than 300 miles when I did this.

Anyway, reducing the idling speed seems to have pleased the computer because although the speed does vary a bit it is not as noticeable as it
was.

If you decide to change the idle speed DO NOT touch the screws where the throttle cables fit.  Those must be left as they are.

The real idle speed adjustment is the large brass screw that is located down in the top of the throttle body and can only be seen by looking down a large hole.

This screw is actually the idle air adjustment and screwing it in (clockwise) reduces the amount of air that passes thru the throttle body thus the engine speed will be reduced.
To increase the idle speed, screw the screw out (counterclockwise).

It only took about 3/16-1/4 of a turn in to reduce my bikes idle speed to a nice fairly steady Thump Thump Thump......
Jim
2011 G5 Deluxe
1999 Miata 10th Anniversary


Chasfield

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Reply #2 on: July 31, 2011, 09:29:25 am
Modern plugs seem to come with a monster gap as standard - which is fine if you have a modern car with blitzkrieg electronic ignition that can produce enough juice to fell an ox.

On my classic Bullet, with Pazon transistor assisted ignition fitted, I gap down to the old school 20 thou. Too big a gap can effectively retard the ignition on a coil and points machine, because the time taken for the EHT voltage to rise enough to jump the gap is extended. Maybe an ECU would compensate automatically for this. I don't know if this would stress such a system or not.
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olhogrider

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Reply #3 on: July 31, 2011, 03:19:09 pm
I am embarrassed to admit this but I threw my NGK in without checking the gap. It works great.


GSS

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Reply #4 on: July 31, 2011, 10:15:22 pm
I am embarrassed to admit this but I threw my NGK in without checking the gap. It works great.
I too haven't checked a gap in a new plug in over 10 years.......cars, jeeps, bikes, lawn mowers, snow blowers, chain saws.......haven't had a single problem with any of the current engines.  Checking gaps in distributors and plugs was almost a monthly undertaking in the good old days! My NGK iridium works great and really improved the running over the OEM plug.
« Last Edit: July 31, 2011, 10:17:57 pm by GSS »
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Arizoni

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Reply #5 on: August 01, 2011, 12:22:29 am
As I recall, my NGK BPR6ES plug came gapped at  .030.

Being the picker of fly feces that I am, I regapped it before installing it to the .028 recommended by the book but I really doubt that .002 would make much difference in a Royal Enfield.

Now, if the bike was being set up for racing where everything needs to be exactly right that is another matter and if the bike had a 10:1 or 11:1 compression ratio that .002 oversized gap might cause some mis-fires but with the 8.5:1 compression ratio of the RE the larger gap shouldn't matter.
Jim
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jartist

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Reply #6 on: August 01, 2011, 04:49:19 am
I think you're right that .002" isn't enough to make a difference but the gap seemed all nice and parallel out of the box and bent over crooked when gapped down.  Maybe it's time for a new gap tool.  I think I'm going to spring for the iridium plug while I'm at it.  Nice thing about the single is that a spark plug is pocket change.  That's why I don't drive a Lamborghini  ;D


Arizoni

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Reply #7 on: August 01, 2011, 05:52:01 am
I may be living in the past but as I recall the spark plug companies don't recommend changing the gap on a iridium plug.

If that is still true you may have to live with the factory setting, even if it doesn't work very well.

Speaking of spark plugs, back in the days of leaded gasoline and regular carburetors  they would get crudded up pretty quickly.

With modern fuel injection and unleaded gasoline the plugs in my Miata, my wifes Toyota and for that matter in my carbonated 1978 GMC heavy half ton don't foul and can go for tens of thousands of miles without changing them.

I can see changing the spark plug in a RE if it is showing a build up of carbon or signs of overheating but those changes are (in my opinion) more a matter of adjusting the plug to suit the style of riding, not to really "fix" something.
Jim
2011 G5 Deluxe
1999 Miata 10th Anniversary


Ducati Scotty

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Reply #8 on: August 01, 2011, 11:53:08 pm
+1 on what Arizoni said.  My idle was at 1500 and would hunt wildly until the bike was really hot, from 1500 down to near stalling.  I set it down to 1200 and it's steady and smooth as silk from dead cold startup on.

I think at speeds a little over recommended idle when the engine is not loaded the ECU gets into a cycle of enrichening and leaning out the mixture that causes the idle to vary widely.  At recommended idle RPM it doesn't oscillate nearly as much.

FWIW this is with the NGK plug.  I tried the stock Bosch plug and it varied less than it did at 1500 but more than with the NGK.  It also idled a little slower with the Bosh so bringing it up to 1200 might have solved it but I'm happier with the NGK so that's what I'm sticking with.

If you have trouble reaching the large, brass idle speed/air bypass screw, just loosen the clamp on the throttle body intake manifold and turn it out to access the screw.  Set the idle, then turn it back to vertical.

Scott
« Last Edit: August 02, 2011, 12:00:46 am by Ducati Scotty »


GlennF

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Reply #9 on: October 13, 2011, 09:53:38 am
Finally got around to changing plugs on my B5 and I threw in a BPR6ES without changing the gap.

Has anyone actually had a problem using the NGK out of the box gap ?


GSS

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Reply #10 on: October 13, 2011, 11:35:03 am
No. Works great out of the box!
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Ducati Scotty

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Reply #11 on: October 13, 2011, 06:13:16 pm
My 7ES was gapped properly right out of the box.  My 6EIX was gapped much larger and I closed it down.  Not sure if that's a difference between 6 & 7 or ES * EIX.

It would probably work just fine with a big gap when it's new but may start to have problems as it gets a little older.  It's always best to gap it properly to start.

Scott


GlennF

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Reply #12 on: October 14, 2011, 01:07:54 am
My 7ES was gapped properly right out of the box.  My 6EIX was gapped much larger and I closed it down.  




NGK are a bit contradictory when it comes to Iridium plugs. They  start out by saying adjust plug gap to suit your engine then go on to say NOT to adjust Iridium plugs, then go on to say well yes maybe you can if you do it the right way  :D

NGK do not recommend gap adjustment for precious metal spark plugs.

A variety of techniques are used to adjust electrode gaps. An appropriate method and tool should be used for gap adjustment although it has come to our attention that a variety of improper methods are used that lead to implications.

When adjusting the electrode gap, the gap may commonly be made too small, as such, the gap may need to be opened slightly. Typically some customers use a lever such as a flat screwdriver to pry open the gap. Traditional Nickel plugs have a solid piece Ø2.5mm centre electrode that may withstand such force. Precious metal spark plugs however have Ø0.6mm fine tips that are laser welded to the centre electrode. These tips are very fragile and not designed to withstand any force. As such NGK will not provide warranty for the breakage of precious metal centre electrode tips.

It is possible to adjust the electrode gap on precious metal spark plugs using an appropriate method that will not place any force on the centre electrode tip.