4 stroking

[milkie62]

What is 4 stroking and how can you tell your saw is doing that ????

 

[Cut4fun]

See if this helps you first, sound wave files to listen to also.

http://web.archive.org/web/20060903154152/www.madsens1.com/sawtune.htm

 

[kevlar]

It is a high speed burble,once you get to know it you will be able to tune saws by ear but it does take a little learning.

 

[Lakeside53]

Even if you do.. it's still just a rough guide.. Best tuning comes from timed cuts.

 

[motosierra]

Would you time your saws cuts at different carburetor setting or are there "timed cuts" tables available for different models of saws?... thanks

 

[Lakeside53]

You have to make your own times and adjustments.. but ...unless you're racing, it's not worth worrying about. Set it for a slight burble with an average length bar and forget it.

 

[motosierra]

That is how I have been setting my saws... with a slight burble.. I have noticed that temperature, humidity and elevation can have an effect on the setting. Cold, dry air packs more punch than hot, humid air and 1000' of elevation can also effect the tuning.

 

[pgg]

If the saws burbling it's running gutless, OK if you're over powered, but no good if you want full power, the shops'll tune your saw to a mere shadow of full performance, covering their butts on warrantees etc.. and the good saws easily handle the extra heat when strung out to full noise

 

[Ekka]

I dunno, I'd personally run my saw on more fuel than air ...

... so I sacrifice 1 second in the cut for maybe 1 year longer life.

 

[rxe]

If you want to hear it, then try my tuning technique.

1) Set up the idle as per normal.

2) Set the high speed way rich. 2 turns out at least

3) Pull the throttle and the saw will climb to maybe 4000 rpm and you'll hear lots of 4 stroking. It'll probably stall out, but you'll really hear what 4-stroking sounds like. You'll also be really safe - there is no chance of leaning out the saw this way.

4) Gradually lean out the high speed until you get to the target RPM on the tach. As you know the sound well, it is easy to hear it coming in.

I just hate the idea of setting it to 1 turn out, and WOTing it...and then realising it is about 1/2 a turn too lean (or whatever). I'd rather start at low RPM (way over rich) and gradually increase, rather suddenly hitting very high rpm.

 

[RiverRat2]

If you want to hear it, then try my tuning technique.

1) Set up the idle as per normal.

2) Set the high speed way rich. 2 turns out at least

3) Pull the throttle and the saw will climb to maybe 4000 rpm and you'll hear lots of 4 stroking. It'll probably stall out, but you'll really hear what 4-stroking sounds like. You'll also be really safe - there is no chance of leaning out the saw this way.

4) Gradually lean out the high speed until you get to the target RPM on the tach. As you know the sound well, it is easy to hear it coming in.

I just hate the idea of setting it to 1 turn out, and WOTing it...and then realising it is about 1/2 a turn too lean (or whatever). I'd rather start at low RPM (way over rich) and gradually increase, rather suddenly hitting very high rpm.

I generally go to 1.5 turns out just to start then out a bit more once warmed up and running till like you say it is 4 stroking real good than bring her in till it picks up RPM then back out a smidge,,, try a cut,,, if it cuts good leave it right there,,,, you will never scorch a piston like that!!!!!!

 

[Crofter]

RXE, i think it is good thinking to tune from the rich side down. The number of turns open is only a rough guide on all but a totally unmodified saw. Whatever you choose for a starting setting if the saw immediately zings to a scream, idle it down immediately and go much richer and climb up from there. The gist of what you are saying is that you should not be listening to a saw scream, too lean and overrevvin while you slowly richen it up. I agree. A lot of saws that have been muffler modded and ported might be running around 3 turns open on the HS screw. Usually you reach a point that more turns open do not make it richer and then you have to ream some of the fixed jets.

Any thoughts about why the saw is not firing every rotation at that rpm, load and mixture?

 

[ShoerFast]

Just my $0.02 worth,,,,,

I like a little 'burble' out of the wood, or in a lite-cut. For me, the best way it seems to get a good timed cut, is when your have long straight knottless log that the bar just barely spans, that way your cutting tecenece and wood variance wont be as much of a factor.

With the good sharp work-chain, DG's set were your saw 'lives best' , back the "H" out till you deffanetely notice a slower cut. Cutting just thin cookie, let the saw do the work, count '1-Mississippi's 2-Mississippi's, till the cookie drops, turn the "H" in like 5 minutes of a clocks big hand, or about 1/16 of a turn at a time, retiming your cut.

Your going have a lot different count - faster cut, each adjustment will be faster then the last is you started with a good-n-fat saw (rich-running) when you get to a point that an adjustment dosant give you much change, you close, when you cut takes a 'Mississippi' longer, back the "H" out a tad, and another 'tad' for you Mom, but like Andy said, you going to be near a slight 4-stroking out of the cut.

Simply, a slightly 4-stroking saw at WOT is running slower with a higher cylinder pressure, under load (in a cut), that cleans up the slightly 4-stroking (safe) WOT adjustment.

What your setting here is the saws air:fuel ratio in a cut for most power, gas will burn anywhere from about 8 : 1 rich (smokes black, incomplete combustion after the flame used all of the O2 and exhaust the left over 'started to burn fuel' ) to about 17 :1 lean (not enough fuel to keep the spake-flame interested and a flame-out condition - lean burning engine , hurts your nose-stinks from the exhausted fuel that didn't get burnt (raw-fuel) after the flame went out) , your best power is having enough fuel to use most of the O2, just as the piston makes it to the exhaust-port, that is also the best place to be for engine longevity, as leaner engines 'run hotter' , fuel cools each stroke on intake, and excess O2 burns hot metals.

Best power is around 10 - 12 : 1 air-fuel ratio.
'

 

[outdoortype]

Just my $0.02 worth,,,,,
....Simply, a slightly 4-stroking saw at WOT is running slower with a higher cylinder pressure, under load (in a cut), that cleans up the slightly 4-stroking (safe) WOT adjustment....

So a slower (richer) adjustment will give a higher cylinder pressure? Perhaps this explains why I tuned a saw with a 16" bar a tad rich changed plug color and sound when I swapped to an 18" bar. The 18" bar the saw 4 stroked until it was almost completely buried in the cut. I know the engine was turning slower but I thought the plug color would be darker/more residue. It was lighter & cleaner with the longer bar.

 

[ShoerFast]

So a slower (richer) adjustment will give a higher cylinder pressure? Perhaps this explains why I tuned a saw with a 16" bar a tad rich changed plug color and sound when I swapped to an 18" bar. The 18" bar the saw 4 stroked until it was almost completely buried in the cut. I know the engine was turning slower but I thought the plug color would be darker/more residue. It was lighter & cleaner with the longer bar.

Utilizing all of the O2 in a cut will be the best 'cylinder pressure' slightly rich at WOT seems to be the best air:fuel ratio in most saws 'in a cut'.

Take an old-skool carburated, automatic-transmissioned car and set the idle screws up to a balanced slightly rich 'roll' in park, then dump it in gear, it smothens out and will sit at at a red light better then 'best' no-load idle, every time.

What may have happened with the 18" bar on that saw, the cylinder pressure maybe came up and it was a better/cleaner burn with the extra heat from the pressure? The 16" in harder wood - duller chain, may have done the same thing?
Your 'on-the-money' with a good color on the plug! Your using all of the O2, no un-burnt black, wet soot , and not to lean were the extra O2 and raw fuel at heat would attack the plug and made a hi-temp glaze.

Edit: Old skool saws, a little more ing-timing (more point gap) would have made more power with the 16" bar,,,,,, but splitting a frog-hair.

 

[RaisedByWolves]

I dunno, I'd personally run my saw on more fuel than air ...

What the hell are you using for fuel?


If you have more fuel than air wont that hydraulic the saw? (ie 51% fuel 49% air?)

Or do you mean that you open the fuel screw up more than you open the air screw?


.

 

[Andyshine77]

I tend to tune a bit rich, my 353, 372 and 7900 all like to run a bit rich. While my 5100 and 361 like to run a bit leaner. I just tune them where they like to run.

 

[Ekka]

What the hell are you using for fuel?


If you have more fuel than air wont that hydraulic the saw? (ie 51% fuel 49% air?)

Or do you mean that you open the fuel screw up more than you open the air screw?


.

Oh, need a toolmakers interpretation for "richer" rather than "leaner", weener. :greenchainsaw:

 

[RaisedByWolves]

Look at that, you Can be taught!



Actually a twofer for me, but I wont rub it in.....



.

 

[milkie62]

Is it OK to give it maybe an extra 1/16-1/8 turn open to make sure enough mixture is going thru it so it does not overheat once you reach the 4 stroking point ??????