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My 13 year old son brought me the spark plugs from the bike yesterday during the 5000 mile service and I had him measure them..........

.028:eek:

I was completely shocked. I don't believe they have ever been out. If they have been out it was when the moco did the 1000 miles svc, cams and tune/dyno.

Anyone ever tightened up the gap to .028 for a reason?

I set them at .042 and noticed it is idleing AND torqueing up better 2up.

I guess when you buy a new Bike you need to check the basics?:rolleyes:
 

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The proper gap is .038 to .043 and according to HD the right plug and plug gap is important for the ION sensing to work correctly with the Delphi ignition system.
The ION sensor replaces the knock sensors HD put in the earlier bikes and it is suppose to help with spark knock by advancing the timing by 4 degrees when the ION sensor detects that the engine is under load or heavy acceleration.
If the bike has spark knock sometimes it will help if the plug gap is wider.
 

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We ALWAYS check the plug gap here.
Never assume they are correct.
Our dyno knowledge has alerted us to .035" on the NGK DCPR8E's we use.:)
Scott
NGK's website recommends a DCPR7E for later model TC's...are you suggesting to use the part number you mentioned. Just curious as I have always used what was recommended, but I will try out the 8E you recommend it. What is the difference between the two?
 

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NGK's website recommends a DCPR7E for later model TC's...are you suggesting to use the part number you mentioned. Just curious as I have always used what was recommended, but I will try out the 8E you recommend it. What is the difference between the two?
The DCPR8E is one step colder heat range plug. The insulator on the colder plug will be slightly larger in diameter and helps to remove the heat from the center electrode which in turn reduces the probability of it becoming a source for pre-ignition. The slightly colder plug works well on correctly tuned motors.
 

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Great suggestion, need to look at mine and see if .035 works better then the .040" that they were installed at.

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In a stock compression motor the .040 gap will work well, higher comp. motors often prefer the slightly smaller gap. An extreme would be our turbo drag car running 26 lbs of boost the plug gap is set at .018. I realize this is not a motorcycle reference but just trying to provide an example of how comp. affects the ability of the plug to fire the fuel mixture.
 

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In a stock compression motor the .040 gap will work well, higher comp. motors often prefer the slightly smaller gap. An extreme would be our turbo drag car running 26 lbs of boost the plug gap is set at .018. I realize this is not a motorcycle reference but just trying to provide an example of how comp. affects the ability of the plug to fire the fuel mixture.
Running high compression in bike. Was having challenge to get spark table to stop adjusting from auto tuner. Well hold on to the grips cause now I got fuel. Just need to put bigger injectors in. It did not change one digit in spark table. Omg 2 months of frustration. Fixed in 5 min thanks to this thread. Thank you:D

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In a stock compression motor the .040 gap will work well, higher comp. motors often prefer the slightly smaller gap. An extreme would be our turbo drag car running 26 lbs of boost the plug gap is set at .018. I realize this is not a motorcycle reference but just trying to provide an example of how comp. affects the ability of the plug to fire the fuel mixture.
Right on!!
It'll actually try to blow out the spark with more compression.
While a tighter gap may not have as large of a spark kernel, it will be more intense.
Our AHDRA Mod Bike @ 17.25 cr, with it's dual-plug system wanted/responded to .020" with the Dyna ignition.
We used to live on our dyno years ago, testing all types of things.
Used to tune 4-5 carbed bikes a day, and mucho knowledge is gained/garnered while that is occuring.:)
Scott
 
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