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post #1 of 21 (permalink) Old 01-16-2011, 01:22 PM Thread Starter
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Spark plug gap

Well time again for plugs.

The manual always makes me wonder what the best end of the

listed spec is better or if there's actually a diifference between

0.038 and 0.043 performance wise on a stock 96" ?

I usually just stab it in the middle and settle for 0.040 .

Any thoughts ?
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post #2 of 21 (permalink) Old 01-16-2011, 01:51 PM
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I believe that is what the mechanics at harley are hoping most will do (split the difference and set in the middle .040-.041) because not everyone has the same feel with a gap gage. One person may think he is gaping at .040 , but if he does not have the proper feel it could be off by as much as .002 plus or minus. So even though he thinks he is gaping at .040 it may actually be .038 or .042.
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post #3 of 21 (permalink) Old 01-16-2011, 05:51 PM
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I don't think there'd be any performance difference between 0.038 and0.043. I would go with 0.038 because if you get too wide of a gap spark may not jump up far. I get my NGKs at 0.034 but that is because of my turbo when it puts out 8 pounds of boost at full throttle the compression ratio is over 13.5 to one. I tried some screaming Eagle plugs but they didn't last very long and once the gap opened up a small amount it run like crap. Even with the NGK plugs if there are gap more than that misfire.
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post #4 of 21 (permalink) Old 01-17-2011, 05:54 AM
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This is why you're given a "range" for your gap. The plug will work fine in that range, but begin to falter, outside of that range.

If the gap is too small, there isn't enough room for enough of the air/fuel mixture to get between the electrode and ground strap, so when the plug does fire there is a chance nothing will ignite. On the other hand, if the gap is too large the spark that does appear will be weak and may not be strong enough to ignite the charge.

The recommended gap is the "sweet spot" for most riders, excluding heavily modded engines and aftermarket ignition systems.




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post #5 of 21 (permalink) Old 01-17-2011, 06:24 AM
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We have witnessed evidence on engines that carry a ccp north of 180, or so, that .035" on the NGK's we use, will show more power, across the board.
It creates a more intense spark kernel, not allowing the increased turbulence, in the chamber, to try to blow it out.
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"....3 dueces and a 4 speed..........and a 389"..........
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post #6 of 21 (permalink) Old 01-17-2011, 10:28 AM
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Quote:
Originally Posted by mrmetal View Post
I don't think there'd be any performance difference between 0.038 and0.043. I would go with 0.038 because if you get too wide of a gap spark may not jump up far. I get my NGKs at 0.034 but that is because of my turbo when it puts out 8 pounds of boost at full throttle the compression ratio is over 13.5 to one. I tried some screaming Eagle plugs but they didn't last very long and once the gap opened up a small amount it run like crap. Even with the NGK plugs if there are gap more than that misfire.
Do you ride this beast often. Does it hold together well?

I found a spark plug chart from NGK that may be helpful for some
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post #7 of 21 (permalink) Old 01-17-2011, 10:34 AM Thread Starter
MPG'S? Who gives a
 
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Just an update...the plugs that came out were over 0.045....

I waited a little long to check my gaps and/or replace.

No noticeable power or performance difference tho.

Great replies !
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post #8 of 21 (permalink) Old 01-17-2011, 12:05 PM
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Hay XRTracker

The only problem I have had is with the screaming Eagles sparkplugs.

I ride it every chance I get and it is held together very well I have had nothing brake on it. I've had the t turbocharger on it for a year and a half so far. Turbo is from Trask performance at a Phoenix, Arizona. If You Want to get some very serious horsepower RB racing. Check out their website.

RB Racing
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post #9 of 21 (permalink) Old 01-17-2011, 12:08 PM
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Quote:
Originally Posted by mrmetal View Post
Hay XRTracker

The only problem I have had is with the screaming Eagles sparkplugs.
Same here. Had a set and developed a miss. Put in Autolite spark plugs and have been fine ever since.




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post #10 of 21 (permalink) Old 01-17-2011, 12:11 PM Thread Starter
MPG'S? Who gives a
 
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Quote:
Originally Posted by Dave63 View Post
Same here. Had a set and developed a miss. Put in Autolite spark plugs and have been fine ever since.
Autolite better than stock H-D's ?
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