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Spark Gap?

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Bret

Bret

Yoda
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Hi Gang,

Question regarding the spark plug gap. I am up-rating my 78B’s ignition system with the Pertronix Ignitor and flame-thrower coil. Anybody have any suggestions as to what I should set the spark plug gaps to, so I can take full advantage of the upgrade?

For a stock system the manual calls out for a gap of 0.035mm. I read over in the Triumph forum that 0.045mm should work.

Any comments or suggestions?
 
Hi Bret,

My 73B has a non-stock engine with a Petronix. I started messing with the plug gap a few days ago. Set it to .035 inch based upon some recommendations and have noticed a bit of a difference in performance. The recommendations I've seen refer to a gap between .030 and .040 inch, based upon having a hotter coil similar to the Lucas Sport Coil.

YRMV.

John
 
<blockquote><font size="1" face="Verdana, Arial">quote:</font><hr>Originally posted by John Staub:
Hi Bret,

My 73B has a non-stock engine with a Petronix. I started messing with the plug gap a few days ago. Set it to .035 inch based upon some recommendations and have noticed a bit of a difference in performance. The recommendations I've seen refer to a gap between .030 and .040 inch, based upon having a hotter coil similar to the Lucas Sport Coil.

YRMV.

John<hr></blockquote>

Hey John,

This is pretty much the line of thinking behind my asking the question. I figured with the hotter coil I’d need to open up my spark plug gaps, but I don’t have access to a dino to pull test runs to optimize for peak performance. That is why I posted, in the hopes that someone may have gone down this dark path already and would be willing to share their info regarding setting the gaps.

One of the more interesting articles I’ve read on Electronic Ignition was by Les Bengtson at the following web address:

https://www.custompistols.com/cars/articles/elec_ignition.htm

In this writing Les makes a good point regarding the advantages and misconceptions of installing hotter “sport type” coils into the MGB.

One of the things he points out is that – “If you are running standard spark plug gaps you will never exceed the capacity of the standard coil to fire the plugs. The Sports Plug is great if you are running larger than standard gaps or are operating at consistently at higher RPMs.”

In his view – you basically are wasting your money unless open up the gap to take advantage of the hotter performance coil.
 
I put the Lucas coil in my 74 MGB. Try .025 to .040 . Start at .04 (or bigger), if there is no spark plug misfire,
reduce the gap by .001 increments to eliminate any misfire.

Hope this helps,
Obtong
 
One thing that happens when you open the gap on a spark plug is that the electrical resistance of the air gap between electrodes increases.
When putting a higher voltage spark coil in the system, it has no trouble jumping that larger air gap. However, those electricities may find a weakness in your electrical system and may find another path to ground. So, you may want to consider putting in good quality ignition leads that are rated for the higher voltage. Of course, the rotor and cap also need to be in top condition.
 
Hi Bret,

I have considerable faith in Les's writings. I've turned to his site (and others) for advice and have not yet been disappointed.

John
 
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