carb and fuel issues

[bwalker]

Are any saw builders flow matching transfers?

 

[glens]

klick...,

He covers the exhaust port at great length.  I'll paraphrase a small portion from memory as best I can having only read through it quickly one time.

Widening the exhaust port is better than haphazardly messing with its timing.&nbsp; If you get it flowing <i>too</i> good, you can run into problems with excessive heat being transfered to the piston, and if you don't precisely match the contours of the sides, you can get ring-pin failure due to the ring being driven laterally within its groove.&nbsp; That's assuming that the port doesn't get so wide that ring life will be greatly diminished and/or that short-circuiting of the fresh mixture becomes a problem.&nbsp; He covers ratios in sizes between the port opening and the exhaust outlet and the tapers involved as well.

Keep an eye out for the "Pay it forward" thread when I offer to put the book back into circulation.&nbsp; It's an interesting read, and I'll likely never do anything with the information myself.&nbsp; There are some things I hadn't considered, but much of it I had an intuition about.&nbsp; It's a pleasure to read; more so than some of the other printed works I've seen in this general (chainsaws and their use) topic, mainly because it's <i>so</i> well written.

Glen

 

[klickitatsacket]

I would definately be interested in it whenyou decide to let it go.

 

[ehp]

Ben a chainsaw is a two stroke motor which everyone knows but they are alot different than most two strokes, the biggest thing is because the motor is built as small as it can be an because of size and weight being a problem , a chainsaw has alot smaller crankcase in volume compared to a motor like a 125cc dirt bike and your saw is a 088 stihl at 122cc, your crankcase volume on a chainsaw is very restictive to make horsepower so you need to play very close attection to your port sizes, if you make your transfer ports nice and big , you will make less horse power in a woodsaw because you have slowed the charge down to much and it lowers your torque band rpm alot

 

[bwalker]

EHP, Smart tuners have known for years that smaller ports make more power, but that doesnt stop the knuckle heads from hogging them out and polishing them. There is a lot more to these motors than timing numbers and going hogwild with a porting tool.
The flow matching I was talking about was done by a guy I have done business with in the past. After he ported the clynder he rigged it up on a flow bench so he could test the flow of one transfer at a time. After taking measurements he adjusted accordingly. He did as much of the actual port work as possible with a CNC. Of course a saw jug is a little tighter area wise. This guy is so meticulous its scarry, but his results speak for themselves.

 

[ehp]

yes Ben i have meet guys like that but on a saw jug it would be pretty hard to get a cnc in there , my flow bench is the wood , if I did it right it will scream if not it will lay down , to any real good engine builder of snowmobile motors or bikes , when they look at a chainsaw jug they pretty much turn up there nose at it cause it is a pretty bad design to begin with

 

[bwalker]

Ed, I think your results speak for themselves. That 026 you built me runs like a raped ape and is getting stonger and stronger all the time as it breaks in. I also notice it likes the rakers ran lower than when it was grefferdized.

 

[Crofter]

I do not believe you can do it by itself and have much of an effect. The atmopheric presure in the crank will only allow a certain volume of fuel. What I try to do is create a condition when the exhaust escaping creates a vacuum I have a direct flow from the exhaust port to the carburetor to get a "jump" on the fuel/air flow. I am creating a "prescavaging" stage.As the piston moves down and increases presure in the crank case; the volume of fuel/air mix (a constant determined by volume of space and atmopheric presure) is then added to the "early" flow of fuel in the cylinder. I only build woods saw, so I then have to tune the exhaust to hold as much fuel in the cylinder as possible. Back presure is actually a good friend to what I am tying to do, although I do still dual port my mufflers but usually to a lesser degree than most.

I see the author is invoking my name as a form of insult on another thread on saw modifications. Says I miss the point. Have a look over this whole thread if you will! I think it must be my posts here that he takes offense at. I cannot think of any other place I have responded to him. Maybe it is his way of explaining things.

 

[bwalker]

I knew he was a bull chitter back then.

 

[Dennis Cahoon]

Come on Frankie....everybody knows you'll argue blacks white. I just ignore you or I'll get a headache!

HAHAHA
Dennis

 

[West Texas]

I agree lucky, this is a good thread; and, I learn from people who are smarter than me; which means I learn from a whole bunch of people.

 

[Crofter]

Sorry Dennis, I really shouldn't mess with your fragile sanity! Take a few aspirins and relax!

 

[ehp]

Frank I guess I didnot read everything again in the start of this thread but I see you were on the ball again like normal, if I am reading this correct Dean brought his Transfer ports way to high and doesnot have any blowdown time , no blowdown = not good

 

[bwalker]

What I try to do is create a condition when the exhaust escaping creates a vacuum I have a direct flow from the exhaust port to the carburetor to get a "jump" on the fuel/air flow. I am creating a "prescavaging" stage.As the piston moves down and increases presure in the crank case; the volume of fuel/air mix (a constant determined by volume of space and atmopheric presure) is then added to the "early" flow of fuel in the cylinder. I only build woods saw, so I then have to tune the exhaust to hold as much fuel in the cylinder as possible. Back presure is actually a good friend to what I am tying to do, although

What a gem this steaming pile of dung is. Go get em, Crofter.

 

[Crofter]

Ben I am not out to get Klikitacksaket. I responded to his original posts about troubles he was having which seemed then to be from departures from common two stroke tuning pratices. A number of other posters came back with similar suggestions but he can do whatever he likes and explain it however he likes. No sweat to me. But when he uses me as an example of some one careless with their facts or missing the point of what a discussion is about, then I take issue. I AM particular about using correct terminology and not attributing some phenomenon to some snake shi+ explanation. I usually have my thoughts pretty well together before I open my mouth. If I am wrong, show me: I like nothing better than facts.

 

[Dennis Cahoon]

So how many ported work saws have you built Frank?....Nothing better than
facts!

HaHaHa!
Dennis

 

[Crofter]

Before I hang up my shingle for something Dennis, you can rest assured I will have done my homework. That's a fact!

 

[Dennis Cahoon]

Yeah Frank....you're the Mang!

 

[Gypo Logger]

While all you culls were fighting and tearing at each other , I sifted thru the whole thread and zeroed in on what Rupedoggy said about raising the metering lever in the carb.
My 980 that I built is experiencing similar symptoms to what Dean described and rather rejet it or start drilling I think I will raise the metering lever as Mike says.
I'll try it a bit at a time and report back and let everyone know how it goes.
In the meantime, keep up the good work and don't let me upset the pissin' match.
John