Dull chains...does it really kill saws....how?

[MustangMike]

4 stroking means the engine develops a burble at WOT with no load, it does not mean that it functions like a 4 cycle engine. It is a "slang" term.

 

[Mattyo]

so you are saying that the burble isn't a misfire....

 

[MattG]

4 stroking means the engine develops a burble at WOT with no load, it does not mean that it functions like a 4 cycle engine. It is a "slang" term.

I disagree (sorry!). Four stroking genuinely is four stroking. The non-linear behaviour of primitive carbs means that they gush too much at higher airflows. And it splutters out the 2 stroke phenomenon. One cycle really is missed - and the lack of purging for that cycle, means the next cycle is lean enough to burn. The drop in power reduces the engine's ability to rev higher.....and thus this effect gives a nice natural rev-limit.

Under load, revs drop, and there's less fuel sucked (closer to stoichiometric) and the engine has more time for a complete burn (think timing advance).

Sorry to get all lecturey, but this is what I've read and heard over the years.

(I'm going home now.....so please don't flame me too much....)

 

[paragonbuilder]

I disagree (sorry!). Four stroking genuinely is four stroking. The non-linear behaviour of primitive carbs means that they gush too much at higher airflows. And it splutters out the 2 stroke phenomenon. One cycle really is missed - and the lack of purging for that cycle, means the next cycle is lean enough to burn. The drop in power reduces the engine's ability to rev higher.....and thus this effect gives a nice natural rev-limit.

Under load, revs drop, and there's less fuel sucked (closer to stoichiometric) and the engine has more time for a complete burn (think timing advance).

Sorry to get all lecturey, but this is what I've read and heard over the years.

(I'm going home now.....so please don't flame me too much....)

Sounds about right. [emoji41]


Sent from my iPhone using Tapatalk

 

[MustangMike]

And if the miss is every 3rd cycle, you think you would know? And, it is likely not a "complete miss", just and inefficient firing. It may even be every 4th cycle, I would bet good money you are not really sure.

And, since it clears up in the cut, it should not be relevant, most of your saw time should be in the cut.

 

[MattG]

And if the miss is every 3rd cycle, you think you would know? And, it is likely not a "complete miss", just and inefficient firing. It may even be every 4th cycle, I would be good money you are not really sure.

And, since it clears up in the cut, it should not be relevant, most of your saw time should be in the cut.

Yeah you're right, if it missed every 3 or 4 I wouldn't notice the difference. In fact my loud music impaired ears aren't great at hearing the tune as well as many others

However, my point was if firing is impaired/missed (call is what you like) when piss revved there isn't a massively damaging thermal strain, and richness at that rev will keep it lubed.

(If anyone is interested I just found a pretty interesting page all about this area https://en.wikipedia.org/wiki/Four-stroking)