What do you consider a plug chop?

[KTM21]

I'm having a discussion with some other blokes on the yamaha forum about what a 'plug chop' is. From what I've seen, a plug chop is when you install a new plug in your bike, do one pull through the gears all the way up to 5th or 6th WOT. Then you kill the bike and coast to a stop. Then you take the plug out, cut the threads off and look at the base of the ceramic to see the size and colour of the mixture band. The idea is that you can tell how well your carb jetting is setup for the main jet. I've seen lots of sources describing a plug chop exactly the same as I just have but the blokes on the yamaha forum are saying that's not what a plug chop is? Just wanted some more opinions

[fq-craigus]

Copied from google (other search engines are available)

A: A plug chop is taking the bike out on the road, holding a certain speed and RPM for one to three minutes, and without changing throttle position reaching over to the ignition or kill switch and shutting off the engine, then pulling in the clutch as quickly as possible and coasting to a stop.

[Joeman]

expensive way to see if your jetting is right!

[KTM21]

expensive way to see if your jetting is right!

Not for me at £2 a plug lol

[KTM21]

Copied from google (other search engines are available)

A: A plug chop is taking the bike out on the road, holding a certain speed and RPM for one to three minutes, and without changing throttle position reaching over to the ignition or kill switch and shutting off the engine, then pulling in the clutch as quickly as possible and coasting to a stop.

Thy're saying there is no cutting threads involved in a plug chop and that you just look at the top of the plug instead of the mixture band.

[Joeman]

my understanding was always that it didnt invlove destroying the plug.

it was just a way to get a good idea what the full throttle jetting was like, so by running full throttle, killing the ignition and coasting to a stop, you basically get a view of how the plug was at full throttle.

Make sure you pull the clutch and shut the throttle..

[KTM21]

Just saw this, Gordon Jennings talking about reading plugs in 1977:

"A lot of amateur tuners, some of whom are fairly successful, will look at some plug freshly removed from a two-stroke engine and offer advice based on the color of the oil deposited on the insulator nose. In fact, if the plug is hot enough there won't be any color, and if there is that still has nothing much to do with air/fuel mixture. If you think about it you'll realize that the only color you can get from an air/fuel mixture is the color of soot. When the mixture trapped in an engine's combustion chamber has more fuel than can be burned with the available air, then combustion will be incomplete and the excess fuel will remain as soot, which is not brown or tan or magenta or any color other than black. And if your engine's mixture is too rich, the sooty evidence will be present on the spark plug's insulator, in a very particular area."

"You won't find any soot out near the insulator nose, on a plug that's running hot enough to keep itself from fouling, because temperatures there are too high to let soot collect. But the insulator is much cooler deep inside the plug body, and coolest where it contacts the metal shell, which is precisely where you "read" mixture strength. Look far inside a plug, where its insulator joins its shell, and what you'll see there if your engine's mixture is too rich is a ring of soot. If this ring continues outward along the insulator to a width of even a millimeter you can be sure the mixture is rich enough to be safe, and too rich for maximum output. In most engines best performance is achieved when the mixture contains only enough excess fuel to make just a wisp of a "mixture ring" on the plug insulator."

http://www.strappe.com/plug_section_16.gif

http://www.strappe.com/plugs.html

[Joeman]

In most engines best performance is achieved when the mixture contains only enough excess fuel to make just a wisp of a "mixture ring" on the plug insulator."

 

And get it slightly wrong and you seize your engine.. two strokes need a good supply of oil to keep them from seizing.

So be very careful if you start leaning out the mixture..

[KTM21]

In most engines best performance is achieved when the mixture contains only enough excess fuel to make just a wisp of a "mixture ring" on the plug insulator."

 

And get it slightly wrong and you seize your engine.. two strokes need a good supply of oil to keep them from seizing.

So be very careful if you start leaning out the mixture..

I did a plug chop yesterday, atleast what I would call a plug chop, and I was running lean, there was no mixture band at all. So I changed from a 240 jet to a 250 and I'm gonna do another plug chop and hopefully I should see a ring. I'm not interested in running lean to achieve slightly more power or anything. My main priority is that there's no risk of it seizing.

[Mr Fro]

Sounds a bit like reading tea leaves. We all did it back in the day - take the bike for a big boy thrash and look at the plug after.

For the sake of 20-30 quid (easily made back in time and not shagging your engine), a dyno run or two is the way to go.

[cockercas]

Dyno run with A/F ratio is around the £50 mark.

[Chrissb6]

my understanding was always that it didnt invlove destroying the plug.

it was just a way to get a good idea what the full throttle jetting was like, so by running full throttle, killing the ignition and coasting to a stop, you basically get a view of how the plug was at full throttle.

Make sure you pull the clutch and shut the throttle..

no need to butcher the plug its the tip of the plug that counts