Four Stroking

Can the "saw masters" provide a simple definition for this??? As far as "tuning the saw" I mean!!

I know the basics of "2 cycle" engines, as I've rebuilt several 2 stroke outboards. I've watched the videos about tuning and such................I still just don't "HEAR" what y'all are talking about as "4 Stroking"!!

 

When it doesn't have a smooth sound from having extra fuel not being burnt.

 

In this video you can hear it pretty good. It goes from rough sounding to smooth sounding once the bar gets into the wood.

 

Did you have the volume turned on when watching the videos? Just kidding...

If you're familiar with 2-strokes then you know a properly tuned one has essentially a high pitch whine of sorts. When one is tuned too rich it gets a lower tone and you can more specifically hear the combustion 'hits'. Some say it "burbles", but it really just sounds rougher so-to-speak. If you pay attention to those videos and listen carefully the properly tuned saws almost sound like they gain rpm when the bar digs into the wood. The way these saws (carbs) operate is that they lean out a bit under load. So, when a saw is just a tad rich and 4-strokes it will lean out just enough to go back to 2-stroking when under load.

My understanding is that the 4-stroking term comes from the fact that the tune at WOT with no load is so rich that combustion only actually occurs on every other trip the piston makes to TDC. Therefore the engine is in essence functioning similarly to a 4-stroke since combustion is not occurring every rotation, but rather every-other.

Make sense?

 

Here is one of my 166 super super fat 4 stroking and then hear clean up in cut.

 

Great basic carb tuning page here. http://www.madsens1.com/saw_carb_tune.htm

 

Going through this myself too. Listening wondering if I got it right, scared I'm too lean. Took a bit to finally felt confident that I got it tuned correct. Suggestion I have is once you feel like you have it where you want, pull the plug and check the color. Too white=bad.

 

I'm much better at hearing the difference in fat through lean now that I've tuned a lot of carbs, but a tach is still my friend in the shop - for folks worried about tuning too lean, a tach is really nice to have. Cheers!

 

http://firewoodhoardersclub.com/forums/threads/so-i-bought-a-660.8004/page-8#post-208103

 

Old design two strokes have a more pronounced 2 stroke - four stroke sound than the new strato charged engines.

The optimum power versus cooling of the engine by the fuel, versus lubrication of the engine by the oil, occurs just above the two stroke - four stroke break point in the old style engines.

 

Depending on the saw (and muffler) I can struggle to hear it. It sounds like a "buzz" to me that cleans up in wood.

 

Here's an attempt at an unconventional way of explaining it:

First, try making a sustained "Z" sound, as if you're imitating a bee's buzzing: Zzzzzzzzzzzzzzzz. Got that far? Okay, now while you're doing that, try pulling the tip of your tongue back away from your front teeth, along the roof of your mouth until the tip of your tongue starts to flutter and make a sound more like a rapid D D D D D D D D D, very similar to a rolled R, made up a series of distinct beats as your tongue repeatedly hits the roof of your mouth.

Four-stroking is like the latter sound, the D D D D D D D, and that's what you want to hear when the engine is running but not cutting anything. The ZZZZZZZZZZZ sound, smooth with no staccato beat to it, is the absence of four-stroking, and that's what you want to hear when you begin a heavy cut. It should switch back and forth between the two, from ZZZZZZZZ in the cut, and then back to D D D D D D D D when you ease up the pressure and the engine doesn't have to work so hard; this is what people are referring to when they say a saw should "clean up in the cut." If it sounds like ZZZZZZZZZZ even when it's not working hard then you're running lean and courting a scored piston. If it sounds like D D D D D D D D even when working hard then you're wasting fuel and performance isn't what it should be.

Not the most thorough or precise explanation, I know, but it's the best I can do at this point along my learning curve.

 

All good stuff above, but don't mistake 4-stroking for hitting up against a rev limiter (if equipped). They can sound a lot alike. That's where a tach is handy.

 

the title of this thread reminds me of Clarence Carter...

 

The smaller the saw and more restrictive the muffler the harder it is to hear. Learned this when I started tuneing.

Muffler modd the saw first and you will hear it better!.

Jon I tried making your sounds and can't get the D D D D D sound??? I guess I can't tune myself to fat???

 

I worked for "Little Debbie" for 9 years. I can assure you proper diligence will certainly result in being too fat...