Chainsaw Porting Theory

[drf256]

I have a one built to 103.5/118/78 was looking for something different...

What would you like to be different?

Cut the piston and chamber flat.

Add finger ports or boost ports.

Add an 044 carb/boot/V-stack.

Build a head.

Open the case sides and add an 028 Super Jug with an 034 piston.

The list goes on and on...

 

[Deets066]

What would you like to be different?

Cut the piston and chamber flat.

Add finger ports or boost ports.

Add an 044 carb/boot/V-stack.

Build a head.

Open the case sides and add an 028 Super Jug with an 034 piston.

The list goes on and on...

In case you guys didn't know, this is the next saw Al is gunna build

 

[Redfin]

What would you like to be different?

Cut the piston and chamber flat.

Add finger ports or boost ports.

Add an 044 carb/boot/V-stack.

Build a head.

Open the case sides and add an 028 Super Jug with an 034 piston.

The list goes on and on...

Is it done yet?

 

[Red97]

Is it done yet?

This ^^

 

[czar800]

What would you like to be different?

Cut the piston and chamber flat.

Add finger ports or boost ports.

Add an 044 carb/boot/V-stack.

Build a head.

Open the case sides and add an 028 Super Jug with an 034 piston.

The list goes on and on...

I'm going to try some different numbers and I didn't want to be way off base.

 

[czar800]

I really wouldn't mind a headed pipe saw also... It's just way over my head.

 

[mdavlee]

I've known some to go as high as 95 on the 026/260. Saw ran good. Wasn't something to lean on real hard but was fun to run.

 

[redlinefever]

Love the info on this thread keep it up guys

 

[David Young]

I've known some to go as high as 95 on the 026/260. Saw ran good. Wasn't something to lean on real hard but was fun to run.

Mike I have a stock one that is that high and I have heard a number of others that were similar.

 

[Time's Standing Stihl]

Bump for a good read

 

[Dub11]

Bump for a good read

I can't read

 

[Time's Standing Stihl]

I can't read

Scroll through the pitchers den

 

[P.M.P.]

Scroll through the pitchers den

That's what I do..

 

[Nutball]

So I've come to learn that "4 stroking" occurs when the mix is too rich to fire. So that combustion cycle goes unburned, and then it mixes with some exhaust days and ignites on the next cycle. If it takes 2 cycles, then it's "6 stroking".

I'm having a hard time understanding why an engine goes from 4 stroking with no load to 2 stroking under load.

You lay the chain into wood, so now you have resistance.

Does the motor suddenly have more chamber heat to burn the mix better?

What's actually happening?

I've recently been wondering why 4 stroking happens. Here are my theories, let me know what you think.:

4 stroking at high rpm (real 4 stroking) is caused when the mixture is so rich it burns slow enough to ignite the mix in the transfers then crank case which then means it misses out on a charge to burn until the next stroke. Changes in engine temp and rpm may cause it to cycle between 2 and 4 stroking when the mixture is on the edge of not burning slow enough to 4 stroke. It will likely lean out in the cut because lower rpm from a load gives more time for the gas to burn, and more time and pressure to heat the engine. Why no significant loss in rpm and torque? Because the next charge of air has little resistance to enter the cylinder, and there's no exhaust to pollute it. So, it burns stronger.

Not 2 stroking during idle may be caused by a very rich tune that requires fresh air mixed in from the muffler to burn properly, or at all. So it fires once, then takes like around 5-20 or so strokes to get fresh air back in the muffler to help fire again. I had a 661 I started when it was flooded, and it idled with literally a 1Hz pop, and maybe a weak pop in between. Obviously the saw won't run at 60rpm.

 

[MustangMike]

The engine is revving so high at the point when 4 stroking occurs that the flow is so strong I can not see that happening.

I concur more with Al's assessment.

 

[Moparmyway]

I've recently been wondering why 4 stroking happens. Here are my theories, let me know what you think.:

4 stroking at high rpm (real 4 stroking) is caused when the mixture is so rich it burns slow enough to ignite the mix in the transfers then crank case which then means it misses out on a charge to burn until the next stroke. .

How does the saw survive if the mixture is ignited in the crank case ?

 

[Nutball]

I was wondering that, but I imagine most of the mix is burned as it blows into the combustion chamber. What's in the crank case may or may not burn, but its pressure can escape through the transfers.

 

[MustangMike]

You would blow a gasket or seal.

 

[bwalker]

Four stroking is simply misfiring or partially combusting.

 

[MustangMike]

Which occurs when the mix is too rich to burn at that RPM, lean it out and blow up / burn up the saw!