i think this is a good question :)

[primo]

i pretty much understand the concept of a plug chop for main jet. now here's a question...

let's say we check out our plugs after pulling into our garage after a normal ride. are the plug color showing the idle jet setting or a mixture of idle, needle, and main?

JP

 

[rizzlo34]

Yes, great question...I will be curious to hear what the tuning experts have to say!

 

[Big R]

After a normal ride, you are going to see the results of all the jets. Only by chopping are you getting the results of each one.

It's not accurate, but just randomly checking your plugs will reveal what the main jet is doing

 

[Hoosier Daddy]

Now I feel stupid...
Associates Degree in Automotive / Diesel Technology, 17 years as a ASE certified Tecnician in GM and Ford Dealerships, countless years at the Drag strip and Street Rod shows, 40 years or reading Hot-Rod, Car Craft, Rod and Custom magazines.
And I have never heard of the term "chop your plugs". Content of the posts I gather you are talking about reading the color of the sparkplugs for fuel mixture, but what gives with the "chopping" ? ???

 

[Big R]

I should have started with "I'm no expert, but....."

Each jet in the carb has it's own function (idle jet, main jet, etc,) but they do overlap throught throttle range. And "chopping the plugs" is cruising down an open road say at 1/2 throttle (pieces of tape on the throttle work good), hitting the kill switch, pulling the clutch, and gradually stopping on the side of the road. Can repeat at 1/4, 3/4, and WOT to check the jets

 

[crazypj]

unfortunately, with modern fuels (oxegenated, alcohol, etc) a plug chop is a waste of time for majority of people.
If its brown/chocolate colour, its too rich
If its pure white/ blistered, its too lean.
a slightly yellow/grey colour is about right for max power and correct mixture (looks lean if your not used to it)
If you use race gas, the jetting will be slightly different to 'street' gas
http://www.ngksparkplugs.com/tech_support/spark_plugs/faqs/faqread.asp
this has better explanation but no pics
http://www.dragstuff.com/techarticles/reading-spark-plugs.html
you need a magnifier and good light

PJ

 

[Hoosier Daddy]

Ooooooohhhhh
Chopping the engine to read the plugs... Got it!
Haynes manuals have a nice picture page but this one shows excessive indications, many 1000's of mile to get them this obvious.

 

[hillsy]

Haynes manuals have a nice picture page but this one shows excessive indications, many 1000's of mile to get them this obvious.

That picture is about 30 years old and is accurate for leaded fuels.....nowadays as PJ has suggested it is pretty much irrelevant.