A little enlightenment please regarding "four stroking".

flashover604

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Hi all. After a lot of Internet sleuthing regarding new saws and tuning I've run across a term that I THINK I understand. FOUR stroking. I've been around four stroke and two stroke engines most of my life. When someone is talking about a chainsaw engine four stroking, this is what I THINK they mean. When the engine is WOT it has a smooth sound but when it's four stroking it gets a sort of "buzz" or miss sound? Am I on the right track? I know on my two stroke bikes if I'm heavy on the throttle and the in the power band it's a smooth sound and smooth power but as soon as I back of it the load drops it goes into the kinda "lopey" condition. Am I thinking of the right thing here?
 
Sounds like you have the idea about right...I believe there are vids online with audio that demonstrate it, if you want to try to locate that resource.
 
I found this video.

http://youtu.be/6kZCSvIYylU

When he lifts the saw you get the rough/burble sound I was talking about. I just wanted to make sure what I was hearing was what I was thinking!

If you mean right at the beginning of the video, then no, that's not four stroking. Four stroking is observed at full rev without load. I'm not sure why that vid is titled the way it is. To my ear, it's not obvious at any point that the saw is four stroking. I could be wrong, my ears are not what they used to be :).
 
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The wav. file on Madsen's site definitely helps. You can definitely hear it "clean up" towards the end of the file.
 
You have to be careful on the newer saws with a rev limiter. When they cut out on the rev limiter it can sound like four stroking. Don't know if they cover that in the vids. Checking your plug color tells you the story.
 
You have to be careful on the newer saws with a rev limiter. When they cut out on the rev limiter it can sound like four stroking. Don't know if they cover that in the vids. Checking your plug color tells you the story.

I totally agree with "spark plug reading"
I sell a lot of saws and all are tuned to "four stroke"
One has to realize that carb adjustment is critical to properly tuned two stroke !
Even changing fuel grade or oil will effect tuning, and even the age of gasoline!
Here is a not so clear photo of spark plug---should be tan (like coffee with lots of cream) or gray.

Spark Plug 3.jpg Spark Plug.jpg
 
"Reading" the plug is probably the best indication of if you have it right .It works on any engine,2 or 4 cycle .Now of course before anybody mentions it on a 4 cycle burning oil it's not always too accurate .Then again it's not too often all cylinders are burning oil .Worst I've seen was 2 out of 8 on a 403 Olds with 290 thousand miles .
 
"Reading" the plug is probably the best indication of if you have it right .It works on any engine,2 or 4 cycle .Now of course before anybody mentions it on a 4 cycle burning oil it's not always too accurate .Then again it's not too often all cylinders are burning oil .Worst I've seen was 2 out of 8 on a 403 Olds with 290 thousand miles .

It takes a trained eye to know for sure. It is also important how the reading is taken.
When checking wide open operation--IN THE CUT--- engine should be cutoff at that time. Best to use a new plug and have someone else switch off.
If this is not done, you will likely get a false reading.
It's not rocket science but needs to be done correctly, or your wasting your time.
 
If you are familiar with the saw and experienced enough you can hear difference in the tone when it four-stroke and hit limiter.
Most newer saws don't like running rich as they don't perform optimal so best is to set them after performance in wood.

If they are lean they get too hot and go kaboom...

Reading plug is a good way to see how it ran over a period of time. Fuel has a lot to do with how it reads as well as setting.
I try to avoid used plugs as they are fairly cheep and washer is only compressed correct once.
I have seen to much problems and costs to do that.
As most here use same fuel its a lot easier.
 
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