MS460 carb on an 039

[RU NUTZ TOO]

I understand how a larger CFM carb can help a saw, but on my 044s and 046s, if they already get enough fuel, why would I want to drill anything out???

Would be different if I could increase CFMs.

this is where the confusion comes in mike. people think if they increase the flow of the low it will improve torque when a saw is loaded hard. not the case at all. the low speed will flow something with the throttle open but almost nothing. when the nozzle is pulling from the chamber it puts a negative pressure in the chamber which pull the diaphragm down to open needle and refill the chamber. this negative pressure pretty well holds all fuel from the low speed chamber. some will flow but so little it doesn't amount the nothing. alot of zama's do benefit from this mod that brewz describes though which is why i figured he was talking to a zama guy.

 

[RU NUTZ TOO]

Deets, planning to run the stock 039 carb against the 460 carb

Nutz, thank you for your input. The more info the better as we are all learning.

The reason we drilled the low speed jet is because the tiny little 0.25mm hole was smaller than the ports in front of and behind the butterfly in the carb throat that spray the fuel into the saw.

I would love to see some fuel curves relative to throttle position

I just picked out a big hard half round that I can noodle into cookies to load the saw up and test cut times.
I had to pull a nail out of it and when i belt it with the hammer it doesn't dint it. It's hard!

It didn't seem to bother my 066 this morning though. JHC that thing is a weapon. Can't wait to port it.

I am stuffed and its stinking hot so the test will have to wait

if you can tune a low speed rich and have it die down there is simply no need to drill anything at all/ when you look at your carb throat you will see one hole in front of the butterfly. this is your idle fuel feed and there will normally be a little notch out of the butterfly right behind it so air can come through and blow over it aiding in pulling fuel from it. behind the butterfly you will see 2 or 3 other holes. these are transition jets which fuel the saw as it start to feed fuel from the nozzle. they also feed from the low speed chamber. without these transition jets the saw will have a serious hesitation off idle (trust me, i've experimented soldering them closed because i damaged them punching a welch plug and figured these issues). with the throttle open full bore fuel comes from the main nozzle. very little will sneak through the low speed. you have to remember that the low speed is actually it's own chamber under the welch plug. the fact that the jet is smaller means nothing. all it has to do is keep this chamber fed so the drill jets after it can remain fed. the difference is the the brass jet you drilled will be fed with a higher velocity then the other drilled jets feed from the chamber. walbro engineers aren't stupid, just zama ones lol. fact of the matter is, you were given poor advice from another site. luckily that advice didn't destroy your carb as i have drilled that jet you did before with no ill affects because it is still controlled by the low speed needle. if that big open hole you drilled was not controlled by a needle you would know. thing would run silly rich.

 

[Brewz]

Nutz, I am not going to discredit the information you have added above, I'm not like that but when I look at flow diagrams for Walbro carbs, some show full flow at WOT and some show little.

I started this thread with my reasons and theory's and plan to test the difference.
I would not say the advice I was given was bad advice at all. Just on a different track to yours.

Until I see definitive facorty flow diagrams showing how much fuel is delivered from which port relative to throttle position, its all conjecture and opinion.

There is always more than one way to skin a cat. Some prefer .22 cal, some prefer .30 cal

 

[Brewz]

I dont think there will be much difference in normal cut speed but I will be interested to see what happens when I push down hard.

 

[RU NUTZ TOO]

Nutz, I am not going to discredit the information you have added above, I'm not like that but when I look at flow diagrams for Walbro carbs, some show full flow at WOT and some show little.

I started this thread with my reasons and theory's and plan to test the difference.
I would not say the advice I was given was bad advice at all. Just on a different track to yours.

Until I see definitive facorty flow diagrams showing how much fuel is delivered from which port relative to throttle position, its all conjecture and opinion.

There is always more than one way to skin a cat. Some prefer .22 cal, some prefer .30 cal

you will figure it. solder the low speed chamber and drill just the idle speed in front of the butterfly. see how it runs, then drill another one behind. i find it really does't matter where as long as it's behind and enters the low seed chamber. then drill one more a little further back still entering the low speed chamber. you will see what i'm talking about. trust me, if we were talking about a zama i would say you got great advice but we are talking about a walbro. you got advice from someone who knows nothing more then zama. think about it. the low and high pull fuel from the same chamber. close the butterfly and it'll pull from that idle port in front, open it slowly and it begins to pull for the transition ports. wide open and there is so much being pulled through the nozzle that the low speed and transition can't flow much. if they did it would disrupt the function of the metering diaphragm. in fact, the nozzle would struggle too if it weren't for the venturi. like i said, i have no doubt the guy you got info from knows what he is talking about BUT he is a zama guy. walbro's don't need the same treatment. most zama's don't either. then again, i personally would never do what i said above. i would just run the 39's jet in the 46 cab, tune, and cut wood. he main thing here a guy has to remember is engineers aren't stupid........... just zama ones lol

 

[Terry Syd]

If you don't like Zama, how about Mikuni? Here's their tuning manual for their diaphragm carbs. Take a notice of their flow diagrams and reference it back to their various combinations on springs, jets and metering orifices.

http://www.mikuni.com/pdf/sbn_manual.pdf

 

[RU NUTZ TOO]

If you don't like Zama, how about Mikuni? Here's their tuning manual for their diaphragm carbs. Take a notice of their flow diagrams and reference it back to their various combinations on springs, jets and metering orifices.

http://www.mikuni.com/pdf/sbn_manual.pdf

won't find mikuni's on saws. those are bike, sled, and jet ski carbs. i would love to see them make diaphragm carbs for saws though.

 

[Brewz]

I had a look in the stock 039 carb and the fixed H jet is not threaded. Its held in with a small cir-clip so they cant be swapped.

 

[Terry Syd]

What? You don't believe the tuning concepts in the Mikuni diaphragm carb manual? I can kinda, you know, understand your dismissal of the results that guys like me, Brewz and Poleman have had tuning diaphragm carbs on saws, but to dismiss MIKUNI?

I thought this forum was going to be different than AS.

 

[drf256]

Happy you're here now Terry.

 

[drf256]

you will figure it. solder the low speed chamber and drill just the idle speed in front of the butterfly. see how it runs, then drill another one behind. i find it really does't matter where as long as it's behind and enters the low seed chamber. then drill one more a little further back still entering the low speed chamber. you will see what i'm talking about. trust me, if we were talking about a zama i would say you got great advice but we are talking about a walbro. you got advice from someone who knows nothing more then zama. think about it. the low and high pull fuel from the same chamber. close the butterfly and it'll pull from that idle port in front, open it slowly and it begins to pull for the transition ports. wide open and there is so much being pulled through the nozzle that the low speed and transition can't flow much. if they did it would disrupt the function of the metering diaphragm. in fact, the nozzle would struggle too if it weren't for the venturi. like i said, i have no doubt the guy you got info from knows what he is talking about BUT he is a zama guy. walbro's don't need the same treatment. most zama's don't either. then again, i personally would never do what i said above. i would just run the 39's jet in the 46 cab, tune, and cut wood. he main thing here a guy has to remember is engineers aren't stupid........... just zama ones lol

What? You don't believe the tuning concepts in the Mikuni diaphragm carb manual? I can kinda, you know, understand your dismissal of the results that guys like me, Brewz and Poleman have had tuning diaphragm carbs on saws, but to dismiss MIKUNI?

I thought this forum was going to be different than AS.

This forum IS different than AS. You're both offering theory and explanations and no one needs to be offended.

Not agreeing with someone's opinion, and offering your understanding of why, is the foundation of learning new things for all of us here.

If we are to feel that we cannot RESPECTFULLY disagree with someone's opinion on a subject (and it seems Nutz did just that) and not get into an all out thread locking fight, what was the point of moving here?

I hope this discussion carries on with differing constructive opinions. I'm enjoying and learning from it.

 

[Deets066]

This carb mod had me baffled too, if you were running out of fuel while you were really cutting hard with the saw then why not open the the H jet instead of the L? I kinda understand your theory that if the L is larger it will draw a little bit more fuel through at WFO. But aren't they both regulated by needles and won't flow anymore than what those needles allow?

 

[Brewz]

The idea was to bolster fuel delivery via the L circuit to increase torque when revs dropped

 

[drf256]

This carb mod had me baffled too, if you were tunning out of fuel while you were really cutting hard with the saw then why not open the the H jet instead of the L? I kinda understand your theory that if the L is larger it will draw a little bit more fuel through at WFO. But aren't they both regulated by needles and won't flow anymore than what those needles allow?

I don't really understand it either Deets, but I see what they're saying.

If I tune a saw in wood, to not 4 stroke at the correct down pressure, I don't see how changing the fuel circuit below that will add much. Maybe for spool up?

I admit I have no idea and just wanna learn this stuff. I still can't tell which is the high and with the low jets.

 

[Moparmyway]

This forum IS different than AS. You're both offering theory and explanations and no one needs to be offended.

Not agreeing with someone's opinion, and offering your understanding of why, is the foundation of learning new things for all of us here.

If we are to feel that we cannot RESPECTFULLY disagree with someone's opinion on a subject (and it seems Nutz did just that) and not get into an all out thread locking fight, what was the point of moving here?

I hope this discussion carries on with differing constructive opinions. I'm enjoying and learning from it.

Well, I certainly agree with you about this not being AS

BUT, I also must admit that shame (westcoaster90 from AS who is now RU NUTZ TOO here) dug a deep hole on AS, and some guys here will have a tough time letting it slide

I hope for the best but have already seen shame delete his posts here and take his ball with him, now he is back.

I'd like to believe that he has turned a corner and has done some growing up, lets see how he carries himself here and hope that he keeps the "old westcoaster" on AS

 

[drf256]

I didn't know he was the same.

Everyone deserves a second chance.

Maybe he won't ruin his.

 

[Moparmyway]

I didn't know he was the same.

Everyone deserves a second chance.

Maybe he won't ruin his.

I am liking what youre steppin in !!
When are we having suds ?

 

[drf256]

Maybe after we plow a foot of snow on Saturday.

 

[Moparmyway]

Maybe after we plow a foot of snow on Saturday.

Yeah .......... I'll be working untill about 14:00, then I have a couple of BIG areas to get cleaned up if we get hit.
How are you fixxed for snow removal ?
Do you need a hand if we get walloped ?

 

[Genius]

Well, I certainly agree with you about this not being AS

BUT, I also must admit that shame (westcoaster90 from AS who is now RU NUTZ TOO here) dug a deep hole on AS, and some guys here will have a tough time letting it slide

I hope for the best but have already seen shame delete his posts here and take his ball with him, now he is back.

I'd like to believe that he has turned a corner and has done some growing up, lets see how he carries himself here and hope that he keeps the "old westcoaster" on AS

Yup, fatbastard90 thinks he can change his name, join a different forum and then act like he is buddies with all the guys he had trash talked over the years on AS.

He now doesn't feel like he needs to be accountable for everything he has said elsewhere.