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http://kawtriple.com/mraxl/carb/plugchop.htm
I'm copying all information from the link above just incase the link is ever 404 or something. See Below.
Plug Chops are a good way to test the jetting accuracy of your carb setup. Simply pulling a plug and looking at the color after running through a variety of throttle positions can be misleading and possibly lead to disaster if jetting is too lean.
The procedure outlined below is intended to test main jet sizing at WOT. It is strongly suggested to begin with overly rich jetting and work your way down in two size increments to avoid seizure. The same procedure can be used at marked mid throttle position to test needle jet position. The distance covered should be at least 1/2 mi, the farther, the better. It may be best to perform the test in a lower gear to avoid excessive speed. Throttle position is the critical item. Variation of throttle position should be avoided and can taint results.
It is possible to examine plugs by using a good light and magnifying glass rather than cutting the threads away. A single cylinder can be used to hone in on the right jetting to save the expense of new plug consumption, assuming all carbs are jetted and setup the same.
Be aware that changes in fuel type/grade and timing can change results.
1. Get new spark plug(s), but don't put them in yet.
2. Warm up motor to operating temp on old plugs.
3. Install new plugs.
4. Accelerate through all gears to top gear with throttle pinned.
5. When you hit the top of the top gear, hit the kill switch and pull in the clutch.
6. Remove the spark plug(s) and ride home on the old plug(s).
7. Hold the new plug in a vise and use a hacksaw to cut the threads away from the center electrode.
8. You should see a brown 2mm "smoke ring" at the base of the white center electrode if the main jets are dialed in perfect.
9. if the smoke ring is darker than chocolate brown or taller than 2mm, you're rich on the mains, but if it revs clean to full throttle, you can leave it there and be on the rich side.
10. If the smoke ring is smaller than 2mm or lighter than chocolate
brown, you're lean on the mains, go up a size and try again.
Chopped plug Illustration:
Below is a series of plug chops ranging from extremely rich to slightly lean.
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Most successful tuners have different techniques they use and using/viewing spark plug as a major tuning tool is a stage we have all gone through. As we gain experience we learn that reading spark plugs does not really tell us much about the air/fuel ratio.
Experienced tuners view spark plugs to select the correct heat range, the best type of plug for the application and an indicator if detonation has been occurring.
The best tuning tools use 3 of your senses and listed it the order that I feel are most important. Hearing, what the engine sounds like. Sense of acceleration and how the engine is performing. Sight, what the piston crown looks like, what the head looks like and lastly what the spark plug looks like.
A spark plug cannot tell the tuner when the engine is making optimum power. A spark plug cannot tell when the air fuel ratio is too rich or too lean. The color of the spark plug, and the length of the soot ring are only an indication of the operating temperature of that part of the spark plug that is being studied. That are many variables that must be considered when looking at spark plugs and trying to get an indication of what is happening inside of the engine.
I commend the person for taking the time and expense to put the above article together but it may miss-guide the average person trying to find the optimum fuel mixture for their two stroke engine. I do not want to offend the person that wrote the article but one of the most important parts of the spark plugs shown above have been cut off and thrown away. No mention was made as to the type of load that was on the engine or the amount of time the plugs were under this load.
I do not want to offend the person that put the above article together but if the majority of the viewers would like me to show the flaws in the above tuning techniques, I will try to do and put all of those sacrificed spark plugs to better use.
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I am always up for better tuning information!!
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Jerry, Have you worked with any Deto-sensors? If so, what are your thoughts?
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Agreed with the more tuning information.
Don't worry about offending anyone Jerry, I found this link on the googles for a quick explanation on how to do a plug chop for another member, But I think everyone here wouldn't mind knowing other ways to tune their bikes though. -
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Jerry, that would be great.
Will gladly replace this with yours.
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I just got my 87 lt250r and having carb issues. If starting with all adjustment screws tufnsx all the way in ' b ow many turns each to set a safe baseline to begin setting carb so jts not to lean. I plan on rebuilding ths carb soon
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Back the flathead screw out 2 full turns. Remove the boot from your airbox to the carb so you can see the slide in the carb. back out your thumb screw (big philips with the spring on it) until the slide stops going down. then turn it in until the slide raises about 3mm then never touch that screw again. after that, just adjust idle via the flathead (air/fuel mixture screw).
Another thing to think about is your throttle cable. Make sure it's set so that the slide is allowed to go all the way down in the carb. -
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In English men.... in English!! Lol. Who can understand this stuff? Adjusting screws till the carb thingy does this and that! I’ll just let a builder set it up and hope for the best!
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