Echo cs 490 porting

[Red97]

Factory piston at bdc. Trimmed the piston to match the transfer in the pic above.

 

[Mastermind]

It's the carb I think.....

 

[mdavlee]

It's the carb I think.....

Wouldn't doubt that a bit. That tiny Venturi can't feed it.

 

[drf256]

@Red97

What number WT carb is on the saw?

I'd like to search for a schematic.

 

[drf256]

More of a porting question,

But how low is too low on an exhaust? I'm sure the answer will vary from saw to saw.

At what point will pressure from the charge become too low to negate frictional and kinetic losses?

 

[Red97]

It's the carb I think.....

Wouldn't doubt that a bit. That tiny Venturi can't feed it.

My only argument to that is the cs 510/20 clammy's spin pretty high with an equivalent or slightly smaller venturi.

Nothing we have tried can get more than 13500. The more I'm thinking about it, I think the timing may be a big culprit..

@Miller Mod Saws
Could you try retarding static timing on your cs500 since it already has carb mods?

 

[Miller Mod Saws]

My only argument to that is the cs 510/20 clammy's spin pretty high with an equivalent or slightly smaller venturi.

Nothing we have tried can get more than 13500. The more I'm thinking about it, I think the timing may be a big culprit..

@Miller Mod Saws
Could you try retarding static timing on your cs500 since it already has carb mods?

I sure will. I've been thinking about doing this one the 6100 as well. It Jacks that saw all up if ya advance it's timing. Even a little. Lol.

 

[huskihl]

My only argument to that is the cs 510/20 clammy's spin pretty high with an equivalent or slightly smaller venturi.

Nothing we have tried can get more than 13500. The more I'm thinking about it, I think the timing may be a big culprit..

@Miller Mod Saws
Could you try retarding static timing on your cs500 since it already has carb mods?

Is the top of the exhaust port at a similar height in the cs510?

 

[Red97]

Is the top of the exhaust port at a similar height in the cs510?

I want to say they are in the 110 range stock.

Think it has a lot to do with the AF setup.

 

[huskihl]

I want to say they are in the 110 range stock.

Think it has a lot to do with the AF setup.

Just wondering. Low exhaust will keep r's down too. Somethings limiting them, that's for sure. I'm guessing it's that jet you guys were talking about that keeps avg Joe from burning his saw up. Gotta id that and smear some jb in it

 

[Red97]

Just wondering. Low exhaust will keep r's down too. Somethings limiting them, that's for sure. I'm guessing it's that jet you guys were talking about that keeps avg Joe from burning his saw up. Gotta id that and smear some jb in it

I don't think it is necessarily that jet. I think it is the volume of air flowing through the venturi.

Yes the porting plays a big role in where the saw will "4 stroke" but I think you can adjust that point to a certain extent with carb size.

Hypothetical example, say your 026 stock carb no filter will 4 stroke at 13.5 but slap a 044 carb on it and I gains roughly 1k rpm. Still f 4 stroking. Because it has more air, and carb can add sufficient fuel for the correct ratio.

Same scenario here, carb can supply plenty of fuel, just can't get the air.

But if you go to big you can loose tuneability and general performance in a work saw.

That all may be bogus, but just trying to explain the way I see it.
By the way arent you in process of swapping a 044 carb??

Can you check the throttle/choke bore and venturi measurements please

 

[huskihl]

I don't think it is necessarily that jet. I think it is the volume of air flowing through the venturi.

Yes the porting plays a big role in where the saw will "4 stroke" but I think you can adjust that point to a certain extent with carb size.

Hypothetical example, say your 026 stock carb no filter will 4 stroke at 13.5 but slap a 044 carb on it and I gains roughly 1k rpm. Still f 4 stroking. Because it has more air, and carb can add sufficient fuel for the correct ratio.

Same scenario here, carb can supply plenty of fuel, just can't get the air.

But if you go to big you can loose tuneability and general performance in a work saw.

That all may be bogus, but just trying to explain the way I see it.
By the way arent you in process of swapping a 044 carb??

Can you check the throttle/choke bore and venturi measurements please

I understand what you're thinking, but you should be able to turn the H screw in and eliminate (nearly, atleast) the fuel above half throttle. The extra fuel is coming from somewhere and drowning it, if it 4 strokes with the H jet all the way in.

I'll go out and measure a wt194

Edit* unless it has a limited coil

 

[huskihl]

Inlet


Outlet


Venturi

 

[huskihl]

I don't think it is necessarily that jet. I think it is the volume of air flowing through the venturi.

Yes the porting plays a big role in where the saw will "4 stroke" but I think you can adjust that point to a certain extent with carb size.

Hypothetical example, say your 026 stock carb no filter will 4 stroke at 13.5 but slap a 044 carb on it and I gains roughly 1k rpm. Still f 4 stroking. Because it has more air, and carb can add sufficient fuel for the correct ratio.

Same scenario here, carb can supply plenty of fuel, just can't get the air.

But if you go to big you can loose tuneability and general performance in a work saw.

That all may be bogus, but just trying to explain the way I see it.
By the way arent you in process of swapping a 044 carb??

Can you check the throttle/choke bore and venturi measurements please

I just reread this...did you want 044 carb measurements?

 

[Red97]

I understand what you're thinking, but you should be able to turn the H screw in and eliminate (nearly, atleast) the fuel above half throttle. The extra fuel is coming from somewhere and drowning it, if it 4 strokes with the H jet all the way in.

I'll go out and measure a wt194

Edit* unless it has a limited coil

I don't notice mine 4 stroking near as well when leaning the high side. Maybe just a bit. Didn't think bout testing without the air filter.

Pretty sure the coil isn't limited, just hits a wall round 13k. Tach dosent go crazy at all.

View attachment 17034

Inlet
View attachment 17038

Outlet
View attachment 17039

Venturi
View attachment 17040

Thank you. That is a small 044 carb...

I just reread this...did you want 044 carb measurements?

Yes please.

 

[huskihl]

I don't notice mine 4 stroking near as well when leaning the high side. Maybe just a bit. Didn't think bout testing without the air filter.

Pretty sure the coil isn't limited, just hits a wall round 13k. Tach dosent go crazy at all.



Thank you. That is a small 044 carb...



Yes please.

Ok..044 carb sizes are...big, bigger, and holyshithowinthehellamigonnafitthatinthere.


Numbers tomorrow

 

[drf256]

I don't notice mine 4 stroking near as well when leaning the high side. Maybe just a bit. Didn't think bout testing without the air filter.

Pretty sure the coil isn't limited, just hits a wall round 13k. Tach dosent go crazy at all.



Thank you. That is a small 044 carb...



Yes please.

Mine still discernably 4 strokes with the needle all the way in. While piss revving, it gets less fat sounding around 1.5 turns out, then turning it further in does nothing.

I didn't have the time to test it in wood. I kinda wanted to keep it a bit fat for the first few cuts.

It was quite strong with the fresh stock chain on the 20 in 18" oak.

 

[Red97]

Mine still discernably 4 strokes with the needle all the way in. While piss revving, it gets less fat sounding around 1.5 turns out, then turning it further in does nothing.

I didn't have the time to test it in wood. I kinda wanted to keep it a bit fat for the first few cuts.

It was quite strong with the fresh stock chain on the 20 in 18" oak.

You are right, I was thinking when I first started mine out of the box was the only time I really messed with the screws. Could only get it around 12k and no 4 stroke.

Was more concerned to see how high it would spin after porting, didn't bother listening to it, juse a quick turn of the h side while watching the tach. Since it was still new, trying to dot it quick.

When I popped the filter it was around 12,900 and still 4 stroking good, but never tried to lean it more.

 

[David Young]

Mine still discernably 4 strokes with the needle all the way in. While piss revving, it gets less fat sounding around 1.5 turns out, then turning it further in does nothing.

I didn't have the time to test it in wood. I kinda wanted to keep it a bit fat for the first few cuts.

It was quite strong with the fresh stock chain on the 20 in 18" oak.

I had a jonsered 535 with a walbro carb that did this exact same thing. I didn't see a brass plug governor in it but I couldn't lean it out enough by ear. when I turned the H in a bit it would fall on its face. I tuned it in the wood and had to richen it up. where it ran the best I would have never tuned it by ear. Put it in the wood it cleared up and would eat some chips.

my vote is there is a limiting circuit in the carb.

I did like your theory about the venturi size so that would be my second guess.

keep us posted

 

[huskihl]

Ok..044 carb sizes are...big, bigger, and holyshithowinthehellamigonnafitthatinthere.


Numbers tomorrow

044 carb HD something, knock off from ddave. It's identical internally to an HD 18 from an 029, but with a larger bore

Inlet


Venturi


I didn't get the throttle bore size, as it's still on the saw