Crank Case Pressure/Vacuum Theory

[BangBang77]

I wonder if an oscillo scope and a pressure transducer would be able to measure the impulse signal fast enough at full throttle.

A pressure transducer may possess the capability to "read" the reality of the cyclical pressure, but to actually view it, the data would have to be trended or charted. For that to happen accurately, the trending software would need the ability to capture data at extremely short cycle times. Having a solid background in machine process control, the cycle time that data can be captured is typically the limiting factor. There are systems capable of doing this, but then money becomes the limiting factor.

 

[Canadian farm boy]

There was a really nerdy guy that connected the diaphragm to a pulse generator and was able to measure its displacement on an oscilloscope. Cant remember if it was here or on AS. I'll find it and it will answer lots of questions.

I think you’re thinking of @chy_farm.

 

[tree monkey]

theory and reality are 2 different things
fuel can't be drawn in to the carb without a pump because there are restrictions in the system

 

[Marshy]

I think you’re thinking of @chy_farm.

Yes, but I cant find his thread on that discussion...

 

[Al Smith]

My Lawdy this puppy could chase it's tail forever until it gets dizzy and falls down .I suppose you could go through two dozen springs in a month of Sundays and set the pop off but who's going to do that ?Obviously they run with the impulse intact or have so far since they invented the diaphragm carb .Before that they ran float carbs used on boat motors and they ran too although not quite as well .

 

[Marshy]

Here it is!
http://opeforum.com/threads/does-a-...ove-vigorously-in-high-speed-operation.11052/

 

[tree monkey]

we need to add a check valve to the gauge. a primer has a light check valve n it. it can be hooked up to show either pressure or vacuum.

 

[XP_Slinger]

Look at the flaps in Dan’s pic. Fuel at WOT should be able to be pulled past this check valves no sweat. Not sure why clamping the impulse line cause such a quick stall.

It didn’t even sound like it leaned out in Steve’s video. Did it?

I heard the 4-stroking go away but it died almost immediately after

 

[Marshy]

Before this thread spirals our of control faster than an oil thread, you might want to review the results from @chy_farm. He has proven the diaphragm pulses up and down through all rpms. Granted, he tested up to 7000 rpm...

 

[Fruecrue]

Before this thread spirals our of control faster than an oil thread, you might want to review the results from @chy_farm. He has proven the diaphragm pulses up and down through all rpms.

I never doubted it.
If a piston can do it, so can a diaphragm and a little flap valve.

 

[Marshy]

I never doubted it.
If a piston can do it, so can a diaphragm and a little flap valve.

Ditto

 

[Fruecrue]

theory and reality are 2 different things
fuel can't be drawn in to the carb without a pump because there are restrictions in the system

Agreed.
A direct path from the tank to high and low speed jets may allow operation in this fashion. But all those valves, passages, needles, twists and turns are too much.

 

[Stump Shot]

It didn’t even sound like it leaned out in Steve’s video. Did it?

I believe that it did. Hard to see with my hand in way but the saw stumbled at first recovered, gained rpm as it went lean then started to die as it ran out of available fuel.

 

[Stump Shot]

There was a really nerdy guy that connected the diaphragm to a pulse generator and was able to measure its displacement on an oscilloscope. Cant remember if it was here or on AS. I'll find it and it will answer lots of questions.

His name is Chy Farm from Japan and he's a pretty cool dude.

 

[XP_Slinger]

Before this thread spirals our of control faster than an oil thread, you might want to review the results from @chy_farm. He has proven the diaphragm pulses up and down through all rpms. Granted, he tested up to 7000 rpm...

That was an impressive read. Thanks so much for digging that up.

Confirms that impulse (pressure & depression) is opening and closing things at high rpm.

 

[Marshy]

His name is Chy Farm from Japan and he's a pretty cool dude.

Yeah, I meant nerdy as a compliment. Very cool thing he did.

 

[CJ Brown]

http://opeforum.com/threads/does-a-...ove-vigorously-in-high-speed-operation.11052/

 

[Clemsonfor]

Most people would consider us "nerdy" !! Chainsaw nerds that is!

Sent from my SM-G900V using Tapatalk

 

[XP_Slinger]

Most people would consider us "nerdy" !! Chainsaw nerds that is!

Sent from my SM-G900V using Tapatalk

Truth! Ha ha ha!

 

[Stump Shot]

There is some very good information that can be had from Tillotson, Walbro and Zama about how a diaphragm carburetor functions. If you look and pay attention to the details most questions can be answered there and I will also say lead you down a smart(er) path when modifying chainsaws for performance. If you think you can't find it the first time, let what did soak in and look again at a later date. I have off and on since the age of twelve years old when I first started rebuilding HR's on snowmobiles and I still can find something today all these years later I bet.