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Author Topic: reading spark plugs  (Read 4645 times)

Offline rsss396

reading spark plugs
« on: July 30, 2013, 01:17:11 PM »








[SIZE=+3]Plug Chop  how-to:[/SIZE]  
Plug Chops are a good way to test the jetting  accuracy of your carb setup.  Simply pulling a plug and looking at the  color after running through a variety of throttle positions can be misleading  and possibly lead to disaster if jetting is too lean.
The procedure outlined below is intended to  test main jet sizing at WOT.  It is strongly suggested to begin with overly  rich jetting and work your way down in two size increments to avoid seizure.   The same procedure can be used at marked mid throttle position to test needle jet  position.  The distance covered should be at least 1/2 mi, the farther, the  better.  It may be best to perform the test in a lower gear to avoid  excessive speed.  Throttle position is the critical item.  Variation  of throttle position should be avoided and can taint results.
It is possible to examine plugs by using a  good light and magnifying glass rather than cutting the threads away.  A  single cylinder can be used to hone in on the right jetting to save the expense  of new plug consumption, assuming all carbs are jetted and setup the same.
Be aware that changes in fuel type/grade and  timing can change results.
 
 
[/HR]
[SIZE=+1]1. Get new spark plug(s), but  don't put them in yet.[/SIZE]
[SIZE=+1]2. Warm up motor to operating  temp on old plugs.[/SIZE]
[SIZE=+1]3. Install new plugs.[/SIZE]
[SIZE=+1]4. Accelerate through all gears  to top gear with throttle pinned.[/SIZE]
[SIZE=+1]5. When you hit the top of the  top gear, hit the kill switch and[/SIZE]
[SIZE=+1]pull in the clutch.[/SIZE]
[SIZE=+1]6. Remove the spark plug(s) and  ride home on the old plug(s).[/SIZE]
[SIZE=+1]7. Hold the new plug in a vise  and use a hacksaw to cut the threads[/SIZE]
[SIZE=+1]away from the center electrode.[/SIZE]
[SIZE=+1]8. You should see a brown 2mm  "smoke ring" at the base of the[/SIZE]
[SIZE=+1]white center electrode if the  main jets are dialed in perfect.[/SIZE]
[SIZE=+1]9. if the smoke ring is darker  than chocolate brown or taller[/SIZE]
[SIZE=+1]than 2mm, you're rich on the  mains, but if it revs clean to full[/SIZE]
[SIZE=+1]throttle, you can leave it there  and be on the rich side.[/SIZE]
[SIZE=+1]10. If the smoke ring is smaller  than 2mm or lighter than chocolate[/SIZE]
[SIZE=+1]brown, you're lean on the mains,  go up a size and try again.[/SIZE]
 

[/HR]
[SIZE=+1]Chopped plug Illustration:[/SIZE]
Below is a series of plug  chops ranging from extremely rich to slightly lean.















Anyone looking for a great builder I highly recommend the following.
For CP products dealers I would recommend:
Arlan at LED(site sponsor), Pete Schemberger at Hybrid Engineering, Mat Shearer at Shearer Custom Pipes, Dennis Packard at Packard Racing, and Nate McCoy of McCoys Peformance.

Other great builders I also would recommend: Neil Prichard, Jerry Hall, Bubba Ramsey and James Dodge.

 

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