First things First.. Safety not just yours but innocent by standers as well. Do Not do this testing in a residential neighborhood. Find a safe strait stretch with good visibility to do this testing. God forbid u slam into some kid on their bike. And don't think it cant happen to you because I promise it can...
Ok now that that's cleared up .
What is the plug chop?
The plug chop is a old school way of tuning a bikes carbs and can be performed by almost anyone with a little since.
When to do plug chop testing?
Any time modifications are done that require rejetting or change the amount of air moving in or out of the motor. If you rebuild your carbs and everything is still at factory specs then you shouldn't need to perform these test. But can if you want to.
Say you hole saw your exhaust to remove the resonators. Generally this does not require a rejet but does require a little turning of the air/fuel screw in order to richen up the bottom end of the carb to eliminated deceleration popping.. Keep in mind that any intake modifications will require more jetting than exhaust modifications.
What you need to know about carbs to do testing.
The big thing everyone seems to ask is were is the air/fuel screw. Well on most of your dual carbed bikes such as the 750 1100 and earlier model VLX's its on the side of the carb in the low corner just before the motor intake boot.
Now for virgin carbs there will be a plug that will have to be removed to gain access to the screw.There's a thread on how to do so. Not going into it here.
Now on newer 2000 model VLX's that use a single carb set up the air/fuel screw is located on the bottom near the intake manifold boot.
The newer single carb VLX's do not have a plug but do have a D shaped screw to deter tampering you can either order the D shape tool or grind a small socket to work..
now that we have the tools we can get started.
First set the Air/fuel screws to the factory setting. Start by turning them all the way in until they are gently seated. Be careful use ur fingertips and dont crank on it you can damage the screw.
Now turn it out to factory spec. Bike specific look it up.
Start with new plugs so you have a nice clean template for your read.
Find a safe place to carry your tools.. I dont suggest just sticking them in your pockets..
Ok fire up the bike and let it warm for just a minuit to get oil flowing... Now put it in gear and accelerate to WOT or wide open throttle for the acronym impaired.. Go threw all the gears wide open.. I dont even let out of the gas to shift i just feather the clutch to take out the bang..
Once uve reached top gear stay in the gas until it fills like the motors pull is dieng away. Grab the clutch and kill the motor.. That's the big red switch next to your thumb on the throttle side.. Maintain holding the clutch and coast the bike safely to a stop.. Hop of the bike grab ur tools remove a plug from each cylinder and get your read..
But wait you don't know what your looking for?..
I haven't forgotten.
First condition and the most dangerous for your motor is the lean condition. Too much air not enough fuel.. Its signs are graying or whitening of the plug.
This can be caused by not a large enough main jet or if you have a adjustable needle such the ones that come with the Dynojet kits you may have it to deep not allowing your main jet to be fully open.
Next condition is the rich condition.. Its signs are sooty blacking or plug being wet.
this is caused by to large of a main or needle position being to high and allowing over fueling to early..
The next condition is the just right condition. Its signs.. Slightly browning or no color Chang at all.. This next pic is strait out of my bike with about 3000 miles on it since my initial tuning..
Now that we have the top end figured out what about the bottom?
Well cruise on back home. On the way give small burst of acceleration and chop the throttle without pulling the clutch. You should hear the bike winding down smoothly with not alot of back firing. 1 maybe 2 pops on a very hard decel isn't uncommon and is more likely in cooler temps. If your getting a ton of popping then likely you need to richen up your Air/fuel screws. Turn them counter clockwise. I like to do mine in 1/8s or1/4s just so i dont go to haywire. And my personal suggestion is if you make it out to 3 1/2 turns to kill a popping problem. Just go up one size on the pilot jet. And set your screws back down to stockish levels. If not you will find that the bike is flooding out when its at a dead stop idling.. Also once you get ur bike tuned i suggest random plug checks for a while just to make sure everything is on the up and up. Say 20 mile check 50 mile check 100mile check. Better to be cautious then broke down.