Two stroke tuning by spark plug color?

[Darwin1138]

After years of bad performance from my Homelite leaf blower, I decided to circumvent all that EPA-do not adjust your carburetor-nonsense, and now it is absolutely fantastic!!!!

Now, I've seen that depending on the tuning, the spark plug deposits are of different colors; if the mix is rich you will have a black spark plug, if it is lean the deposits are white/grey and if the mixture is correct then the spark plug is brown.

The question is how much time of operation does it take to see this? And if this happens in a used plug that has deposits by now??

For example, the plug in my leaf blower was totally black, I cleaned it a little, reinstalled and then adjusted the carburetor; if I adjusted the carburetor correctly, will the plug turn into a brown color? Or do I need to install a new plug to see this?

 

[IndyIan]

A new plug is best to see what's going on faster.
Usually you can tune just based on WO rpm and the amount of missing, but a blower always has load on it so I don't know how well it would work. Also you have to know if there is a rev limiter in the ignition as that may make it miss but the motor could still be lean.

 

[Phishin]

Do you have one or two adjustment screws (idle and WOT....or slow and main jets)?

 

[eddy21]

You would need to kill it from wide open . If you let it go to idle it will throw off your reading. I don't think there's that much adjustment to that simple carb . mostly idle mixture and they probably made it rich to be on the safe side.

 

[Oil Changer]

This is the best advice I've read on this deteriorating forum in a long time. We used to call it a "plug chop".


Originally Posted By: eddy21
You would need to kill it from wide open . If you let it go to idle it will throw off your reading.

 

[Darwin1138]

My carburetor has two screws (L & H) and I tuned it following some other posts here and some other info I found on the web.

The engine doesn't need to be run at half choke now and it doesn't stall, in short is better now than when it was new. That is the reason for the

I am asking this not to adjust the carb but more as a way to verify that the tuning is correct.

 

[Darwin1138]

Originally Posted By: Oil Changer
This is the best advice I've read on this deteriorating forum in a long time. We used to call it a "plug chop".


Originally Posted By: eddy21
You would need to kill it from wide open . If you let it go to idle it will throw off your reading.


Hey this "plug chop" thing is interesting, I will get a new plug to try this method, but this also tells me that the color thing is a rapid phenomenon so I will remove the spark plug after work to see what is what.


More info about plug chop:
http://www.mopedarmy.com/wiki/Plug_chop

 

[Chris142]

I dont think this new gas works well for tuning. It burns too clean. But then mounting an air fuel ratio sensor to your leaf blower is out lol.

 

[Darwin1138]

It changed color!!

I removed the spark plug and to my surprise it was of a brown color, sorry for the image but the macro in my camera would not turn on.



So to answer my own question: the plug changed color, from totally black to brown, with just a couple of gas tanks of use, a little more than a liter or about 4 hours of use.

 

[asand1]

http://store.chainsawr.com/blogs/tuning-...nsaw-carburetor

Quote:

An adjustment that is too rich will cause a saw to smoke, have insufficient power, result in additional carbon build up and may damage the engine. An adjustment that is too lean will also produce insufficient power and is more likely to damage the engine through lean seizure.


When tuning a two stroke you really don't have time to run it and read the plug. You do it by ear.

 

[wag123]

Reading the spark plug is NOT how you adjust the carburetor on a 2-stroke.
If you have a fully adjustable carburetor, get the engine hot, then adjust the low speed (idle) mixture first, screw it in until you have a lean idle drop-off then back it out about 1/4 to 1/2 turn. If the engine hesitates or wants to die when you give it throttle, you have the low speed mixture set too lean. Turn it out another 1/4 turn.
Then you adjust the high speed mixture by running it wide open and turning the mixture screw OUT (rich) until the engine 4-cycles, then turn it in (lean) just enough for the 4-cycling to stop. This procedure is assuming that the engine is under a full or nearly full load, a blower always is. You can NOT adjust a chainsaw or weed eater like this or it will be too lean. Without a load, a 2-stroke engine should ALWAYS be adjusted to 4-cycle a little at full throttle.
Technically, now days the manufacturers want you to adjust the carburetor using an accurate tachometer, but the above adjustment procedure is what we have all used for MANY years, long before we had accurate tachometers to use.

 

[Lubener]

Found this interesting article on this subject.

http://www.autorepairinstructions.com/?cat=9

 

[Team_FAST]

Wag123's reply is spot on! The only thing I would add to this is tune the low speed screw for throttle response. It should be snappy when you open the throttle. Usualy the LO speed screw will richen it up such that the idle stop screw will need to be opened a little to compensate. Set the Hi speed setting as stated before...easy to do with a blower.

I did this to my little weedeater featherweight blower....combined with a muffler mod (ported muffler) and was amazed at the improvement in performance. Also starts a lot easier. You don't really gain much overall airflow out of the blower itself, however.