Old School Spark Plug Road Test?

[karls59tr]

I've got the rebuilt carbs more or less set up and I'd like to have a look at the plugs while out on the road. If I remember correctly you take it up to a certain rpm?...shut the motor off...coast to a stop and check the plug condition? Am I on the right track here?

 

[Deleted member 8987]

Yes.
They key is to place vehicle in neutral and shut it off, coasting to a safe roadside stop to check sparking plug condition.

I never did a pre-set rpm test, just took it to normal road speed of about 35 or 40 in 4th, kept it there without wobbling the accelerator (steady), and shut it off.
Usually a couple of miles to make sure any loading was burned off.

 

[Dale]

Reading plugs has always seemed a black art to me. Quickly becoming a lost art too, I fear. Your regimen sounds appropriate. As I remember we didn't want the engine to be idling or on overun long, before we took a reading. Chocolate milk brown was supposed to be the ideal color on the insulator tip. There, you have the sum of my experience. Though I could share some stories of some miss reads that cost me dearly. Good Luck. It's as good an excuse as you need for a spirited drive.

 

[Geo Hahn]

I have heard of the need for a 'dead stick landing' to get an accurate reading but I just look at them in the garage after the car is parked without being idled for long. The toasty brown is there without all the roadside drama.

 

[poolboy]

You seen this ?
https://www.dansmc.com/spark_plugs/spark_plugs_catalog.html

 

[AEW]

This is for regular leaded gas right??? I believe the desired brown is oxide of tetraethyl lead. Modern fuel gives mostly black soot if aything. Has anyone talked about taking along one of the cheap lazer thermometers and shooting the exhaust manifold up at the head branches?? Or just spit on your finger like an old Ferrari mechanic and listen for the sizzle :wink: Or... like an old Porsche mechanic and decide if it will do 125 it must be tuned...

 

[poolboy]

Maybe. That particular chart is from 77.
Probably some later versions on the net.