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Carburetor butterfly valve modifying

popopboat

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Hello, so im new to porting and "tuning" chainsaws and today i tried to modify a bit carburetor, mainly butterfly valves (choke and throttle).
I sanded both valves to more than half thickness, polished them and also sanded/ground shafts to a bit more aerodynamic shape - elliptic, to decrease turbulences.
Also smoothed out tiny bit a carburetor intake side.

After reassembly I started chainsaw and it four stroked like crazy, ran very very rich (but in progress i never touched adjustment screw) and i finished my work toolate so i couldnt test it on a nice piece of wood , does that mean that i somehow messed up and now it sucks less air ?

Paint sketch of what i exactly did : https://ibb.co/wh2MPDd

What do you guys think?
And what do you gennerally think about doing this? Worth doing it or shouldnt be done at all?
 
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Gord

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Never really thought about it that much, just been happy with a good running carb and IMO what it services is what really makes a difference in power gains - porting etc.
 

Ronie

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Have you readjusted the carburetor yet? If you have. do you feel like you gained anything from it?
 

popopboat

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Yep, readjusted, unfortunatelly cannot tell RPM, dont have meter, but can surely say that power actually noticeably dropped :/
Chainsaw seems sluggish, even at accelerating...
But I made a mistake, should have first tried that only on choke valve but not on both and then see results, because as i researched throttle shaft has to be round to actually make turbulences for better air/fuel mixing, but not sure for choke shaft because its before jet/nozzle so maybe it would work on it...
And on throttle shaft !maybe! a polishing would work a bit, bot nothing else..

Maybe someone with more experience and spare equipment could try this out and make actual notes on results :D
 

huskyboy

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Not my pic... but this is exactly what I do. 75A34C94-146B-4C8B-BE46-90B5173AF342.jpeg Don’t make it too thin or you will break the shaft in use. Tape off the carb holes and use a shop vac to get all the filings as you are doing it. Not easy to do. Yes there is a gain. Small though. They all add up...
 

popopboat

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This one is choke valve right?
How about throttle ?
 

Nutball

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Maybe take apart the carb and flush it out with fluid (carb cleaner or WD-40 or something) you might have a metal filing where it shouldn't be. I recently did a similar thing to a carb, and the high speed got no fuel. After cleaning it started working again.

Yours could sound like it is 4 stroking a lot because it is now able to rev up faster with the modified carb, and higher rpms are more likely to 4 stroke.
 

popopboat

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maybe i made mistake when testing yeah, lack of equipment hehe
ill revisit this experiment once i get tachometer, and actually check rpm

maybe i actually improved air velocity in carb and by that more "agressive" venturi effect, so it sucks more fuel also...
and by that, does anyone know some cheapo tachometers online?
 

Nutball

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I am, I'm free, just make a good video or sound recording of the saw revving max rpm for a few seconds and I can give you a good idea of the rpm.
 

Wonkydonkey

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If you get a tach, make sure is a 20k one..and the quicker refresh the better.
 
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