No True "Plug Chop" for Scooters

[Wheelman-111]

Greetings:

To test the adequacy of the Main Jet size on motorcycles, some advocate this procedure:
On a dark Desert Highway, cool wind in my hair... Run the bike up in top gear for half a minute.
Hit the Kill Switch AND SIMULTANEOUSLY pull in the clutch to capture the plugs' appearance at the moment of peak RPM at WOT.
Otherwise, the engine continues to vacuum up unburnt mixture as it coasts down, which will wash away the plug's True Colors and skew the test.

Now I submit that it's impossible to do this with an auto-clutch that you can't disengage. Short of locking the rear wheel, coast-down will alter the plug color every time.

What say you?

[Johnny5]

Makes perfect sense Wheelman. I've always admired your logic. I suppose one could do a 10 second wot on a center stand with moderate braking applied to simulate a load. Then cut the ignition. Of course this is wear and tear on your brakes, not too much I'd imagine. I wouldn't recommend it to some of you guys w/ crazy power 80+cc kits. The only chop you'd perform is on your shoes!

Any other ideas? Like a dyno with a brake?

[Trafficjamz]

What "washes" the color away?
Is it the gasoline?

Find a way to cut fuel?

Cut the belt?

[turtle13]

You know I had never really thought about it that way, but it makes sense. Probably the closest way would be to hit the kill switch at WOT, and pull the plug to check the color. You cant loose too much color from a completely unburnt mixture as you slow down...

[Wheelman-111]

Greetings:

The Esteemed TrafficJamz axt:

What "washes" the color away?

The answer is in the first post:

Otherwise, the engine continues to vacuum up unburnt mixture as it coasts down, which will wash away the plug's True Colors and skew the test.

Gasoline can be an excellent solvent to "clean" dirty parts. And alter plug color. Hence the term "Plug CHOP".

[turtle13]

Yet still in theory, on a motorcycle if you pull the clutch and hit the kill switch the engine is still spinning, producing vacuum and pulling gas through the carb, therefore still past the plug...
Just playing devils advocate...

[Trafficjamz]

When we did most of our plug chops, most of the scooters still had stock gears or stock variators.
This made it easier to do chops because stopping quickly from only 35mph isn't so bad.

It's a plug chop......it's not super accurate anyhow is it?

For better tuning get CHT or EGT gauge.

[Trafficjamz]

Yet still in theory, on a motorcycle if you pull the clutch and hit the kill switch the engine is still spinning, producing vacuum and pulling gas through the carb, therefore still past the plug...
Just playing devils advocate...

Yeah for a half a second or so.



These higher cc mopeds can take a long time to stop from full throttle.

[Wheelman-111]

Greetings:

Yes, to get the most accurate representation of the plug color, one would have to brake as hard as possible in addition to killing the ignition. I agree the CHT or EGT gauge is a better way to tune, but not everyone has one.

[Bear45-70]

Wheelman is of course right but, just close the throttle to stop the major influx of fuel that can wash the plug.

[konaking]

Is that why I may have gotten a bad reading? Hmm tommorow I'm gonna do a chop and stop as hard as I can after I kill the throttle

[Bear45-70]

Is that why I may have gotten a bad reading? Hmm tommorow I'm gonna do a chop and stop as hard as I can after I kill the throttle

Kill the ignition, close the throttle and brake like *.

[konaking]

Kill the ignition and close the throttle?????? I've been going wot for about ten seconds then killing the ignition with the throttle wide open then rolling about ten feet with the throttle open til I stop. So your saying after the bike is cut off at wot I sould release it? Hmmm interesting darn.

[Bear45-70]

Kill the ignition and close the throttle?????? I've been going wot for about ten seconds then killing the ignition with the throttle wide open then rolling about ten feet with the throttle open til I stop. So your saying after the bike is cut off at wot I sould release it? Hmmm interesting darn.

Leaving the throttle open allows the engine to suck major amounts of fuel thru the main thus allowing that fuel to wash the reading off the plug. Also how the * do you stop in 10 feet from max speed. Not just wide open throttle, but at max speed for at least 15 seconds, then kill the ignition, close the throttle and brake like *. Then read the plug. Best to carry a spare plug to install in the engine for the ride home. I've carried as many as 5 new plugs and done 4 plug chops then read the plugs when I get home and am at my bench.

[konaking]

Well I do the chop right before my house so I don't need to wrench on the side of my house. Ill post some pics up tommorow of my chopp. By the way bear you da man