I can't follow this "suck back" thing

[bwalker]

I still am not buying it. That is to say I dont think its possible for a engine to "suck Back" enough to digest debris.
Flow reversals can and do occure, but the occur in fractions of a second, even with a tuned pipe.
For a little back yard fun place a hand full of flour in front of the stinger on a tuned pipe and get back with me.

 

[RiverRat2]

I think they ought to drug test all of yall

:spam:

 

[Lakeside53]

Who's "they"?????

 

[RiverRat2]

Who's "they"?????

Whoever's in charge,,,,, I dunno????? :spam: :spam: :spam:

 

[THALL10326]

:spam:

I just got off the phone with my man at Stihl about the now famous "SUCK BACK". He got a good laff too at the name. He said in so many words there is no suck back. I said ohhhhhhhhhhhhhh noooooooooooooo the thread will die, let there be suck back,LOLOLOLOL

There is pressure back to the exhaust port from the muffler but as for sucking in debris, no.

 

[RiverRat2]

I know Tha Suck Back Police!!!!!!!

Who's "they"?????

:smoking: :smoking: :smoking: :crazy1:

 

[ChuckinOhio]

And now my new found beliefs are crushed by the voice of STIHL!!!:biggrinbounce2:

I still am going to peek in ye olde mufflinator once and again to see if any foreign objects are rattling about loose. Probably should have been doing that anyways right?


Chuck

 

[Poley4]

Suck back is real!

Suck back is a real problem. I have experienced it many time with chainsaws. It is not necessarily dangerous, but it is rather unpleasant. You know when you are standing at the parts counter at the local saw shop and the man behind the counter tell you just how much that little part is going to cost to fix your saw. And the sound the air makes rushing into your lungs through your clenched teeth and your butt puckers knowing your fixing to get screwed but your not getting a kiss. If this has ever happened to you, then you too have experienced suck back!

 

[jhellwig]

Since when did the throttle butterfly completely close off the throttle? The only pressure drop is when the piston is moving up. If no new air is coming in then no air is leaving. You will just compress the same air over and over.

 

[Crofter]

Since when did the throttle butterfly completely close off the throttle? The only pressure drop is when the piston is moving up. If no new air is coming in then no air is leaving. You will just compress the same air over and over.

The throttle plate does not close completely. I suggest an open area though that is ~.01 of a square inch. often ( if you have really large muffler opening) the plate must be completley shut in the bore to get low enough idle, leaving only the small notch in the bottom of the plate above the low speed inlet orifices to admit air, so in relation to the piston displacement and the exhaust port opening area, the intake is virtually shut off. You are right in saying there is a lot of compressing and expanding the same material. During the piston travel up and down while the exhaust port is open would be when there is transfer back and forth thru the exhaust port. Because of the dampening effect of the muffler volume there is likely no reverse flow at the muffler exit but only pulses of little and greater flow.

 

[RiverRat2]

There is pressure back to the exhaust port from the muffler but as for sucking in debris, no.

Ahhemmm!!!! and tha Champ has spoken!!!!!

what about it Crofter are you gonna do some sort of trial in a controlled environment with a super slow motion camera,,,, or are ya just keep layin down tha smack on Suck Back????

Actually there is a real Suck back preventor that one must have On 084> class saws (especially with fresh rings) it called a de-comp button,,,,

It keeps yo hand and arm from getting sucked back into the starter recoil when its cold!!!!!!!!!! :monkey: :monkey:

 

[2000ssm6]

Ahhemmm!!!! and tha Champ has spoken!!!!!

what about it Crofter are you gonna do some sort of trial in a controlled environment with a super slow motion camera,,,, or are ya just keep layin down tha smack on Suck Back????

Actually there is a real Suck back preventor that one must have On 084> class saws (especially with fresh rings) it called a de-comp button,,,,

It keeps yo hand and arm from getting sucked back into the starter recoil when its cold!!!!!!!!!! :monkey: :monkey:

I can see that happening on a 10 degree day My 044 does that suck back thing every so often and I call it a sob. After the name calling it gets better. I say, "that's right you sob, no more suck back".

 

[Crofter]

Whoa! River Rat. The info Thall came up with does not conflict at all with what I am saying. I am not saying the muffler sucks in debris. I am saying that there is flow reversal at the exhaust port that can dilute and affect mixture. If you do get dirt into the muffle it could get into the cylinder though I suppose. I keep a screen on mine. That is not my focus though. It interests me how the back pressure and length etc. of the exhaust runner affects the operating characteristics of the engine especially when you start doing muffler and engine port modifications. As for me doing an experiment to demonstrate flow reversal at the exhaust port, that has already been established. Here is a link to the kind of research that does go on. http://www.adapco-online.com/adapco_online/user_arts/mot2strk/index.html

 

[RiverRat2]

Whoa! River Rat. The info Thall came up with does not conflict at all with what I am saying. I am not saying the muffler sucks in debris. I am saying that there is flow reversal at the exhaust port that can dilute and affect mixture. If you do get dirt into the muffle it could get into the cylinder though I suppose. I keep a screen on mine. That is not my focus though. It interests me how the back pressure and length etc. of the exhaust runner affects the operating characteristics of the engine especially when you start doing muffler and engine port modifications. As for me doing an experiment to demonstrate flow reversal at the exhaust port, that has already been established. Here is a link to the kind of research that does go on. http://www.adapco-online.com/adapco_online/user_arts/mot2strk/index.html

Don't mind me I m just havin fun,,, if you wanna see some suck back in action!!!! opcorn:

Fire up an 066 with out tha muffler,, after you've done a fresh topend (saw all cleaned of course) and just let it idle a bit and heaven forbid barely blip tha throttle a time or two and let it idle back down you dont have to rev it much and it will have a very unusual distinct undualating popping sound and you can really see the amount of raw fuel that it spews out that is why when a two stroke is cold they do have a tendency to smoke just abit, and the muffler actually helps control RPM with the back pressure it produces and helps burn or vaporize the excess raw fuel...................

 

[THALL10326]

Whoa! River Rat. The info Thall came up with does not conflict at all with what I am saying. I am not saying the muffler sucks in debris. I am saying that there is flow reversal at the exhaust port that can dilute and affect mixture. If you do get dirt into the muffle it could get into the cylinder though I suppose. I keep a screen on mine. That is not my focus though. It interests me how the back pressure and length etc. of the exhaust runner affects the operating characteristics of the engine especially when you start doing muffler and engine port modifications. As for me doing an experiment to demonstrate flow reversal at the exhaust port, that has already been established. Here is a link to the kind of research that does go on. http://www.adapco-online.com/adapco_online/user_arts/mot2strk/index.html

Crofter from what the man told me at Stihl you've been 100% right all the way through this thread. Good job!!!!!!!!!!!!!!!!!!

 

[bwalker]

Am I the only one thinking "who gives a shat"?

 

[THALL10326]

Am I the only one thinking "who gives a shat"?

LOLOL, good point. Must admit this thread is a fun one though Ben..

 

[RiverRat2]

Am I the only one thinking "who gives a shat"?

Nope!!!! 2shats

 

[GASoline71]

Make that 3...

Gary

 

[manual]

Crofter from what the man told me at Stihl you've been 100% right all the way through this thread. Good job!!!!!!!!!!!!!!!!!!

So does this mean you are going to buy his book ?
Crofter the Man that Stihl agrees with. LOL