Stihl ms 460/660 Hybrid. 469e

[Canadian farm boy]

Just my $.02 but I honestly think that boring the Venturi is gonna be a step backwards. Thinning the choke and throttle shafts as well as screws would help if you just want a little more air flow. You could even delete the choke if you wanted. Maybe try removing the choke and air filter and make a couple cuts with the saw and see what happens.

 

[NateSaw]

This.

Sometimes there is no need to change the venturi at all. Just the bigger throttle bore makes a real change. More fuel.

Other times changing only the venturi will buy more air and less fuel. It depends what you need.
And where your idle jets are located.

On yours, I wonder if just going back to the original jet size would make a better top end. Many people
over carb a saw and just make it harder to find the good tune. You gained roughly 7cc, is that enough to matter?

It’s a rabbit hole. It can create a lot of idle and throttle up issues when you start boring the carb. Jet, bore, venturi all change your ratios. I spent as much time fighting the carb on one hybrid than the whole rest of the build.

I feel strongly (I know, feelings aren't facts) that more air is needed. It tunes just fine now! But there's room for a bit more air. We've reached the point of fine tuning for sure. I'm ordering some welch plugs so I can get my learn on in there. I've read some valuable stuff that @Canadian farm boy has posted about carbs. I'll have to reread all of it. But it soundlike changing bores and venturi effects the flow of the air jets and may require some adjusting. It is certainly attractive to consider swapping out the jet though, so that should be numerous uno. I'll have to Rob one from a 50a,and try it immediately!

 

[NateSaw]

Just my $.02 but I honestly think that boring the Venturi is gonna be a step backwards. Thinning the choke and throttle shafts as well as screws would help if you just want a little more air flow. You could even delete the choke if you wanted. Maybe try removing the choke and air filter and make a couple cuts with the saw and see what happens.

Glad to have your 0.02$. That's worth at least 50$. What's your PayPal?

 

[Loony661]

The only the thing a carb that’s too small will limit, is RPM. Period.

I don’t think your carb limited with only the 7cc jump in displacement..

 

[NateSaw]

On the subject of choke delete, for me, it is imperitive this build maintains full functionality as is oem. I know that sounds perfectly contradictory, but, I'd love to be lucky enough to have a solid work saw out of this. @huskihl will be disappointed if it offers ease of use and longevity though

 

[NateSaw]

Then I vote to go to a one size smaller jet and let it rip.

 

[Loony661]

Then I vote to go to a one size smaller jet and let it rip.

If you close the H screw, do you gain RPM?

 

[NateSaw]

If you close the H screw, do you gain RPM?

Ii do now. Since the intake port tine/area change, I can now take it out of 4 stroke at wot.

 

[NateSaw]

Perhaps I should be more focused on evening and flowing the uppers, carefully widening the lowers. Outside of that, and carb mods, I don't think there's any more juice to squeeze. Idk.

 

[Loony661]

Something to think about: I was always told that mixture screws are no longer effective beyond 3 full turns out. So if you are within 3 turns on your H mixture, changing the jet size will only cause more problems.. That is, if you are getting the saw to “4stroke” WOT no load, within 3 turns, your carb is not the problem. My 2 cents.

 

[NateSaw]

Something to think about: I was always told that mixture screws are no longer effective beyond 3 full turns out. So if you are within 3 turns on your H mixture, changing the jet size will only cause more problems.. That is, if you are getting the saw to “4stroke” WOT no load, within 3 turns, your carb is not the problem. My 2 cents.

I don't think I have any problem, perse... I'm chasing power. I'm at 1 1/4 turns out, running nice. That's how I can tell I have room for more air. It's really that simple. I used the high screw to diagnose lack of air from the word go. It was precisely that, I could kill the saw turning the screw in, that illuminated the lack of air caused by the boot kinking. Fixed boot with riser, it got better... But I could still tell it wasn't revving to the moon killing the high circuit. Widening port and opening at 80* fixed that. Now, I'm just chasing power. More rpms would be alright too. My logic this morning at 4am,was to bore the throat of the carb to match the wj throttle plate, then match the Venturi diameter to the wj. Choke side is with a thou already. Was going to leave that. None of this is necessary, really. I feel if I have some margin left over on the carb side, gentle port changes will make the difference they should.

 

[huskihl]

Something to think about: I was always told that mixture screws are no longer effective beyond 3 full turns out. So if you are within 3 turns on your H mixture, changing the jet size will only cause more problems.. That is, if you are getting the saw to “4stroke” WOT no load, within 3 turns, your carb is not the problem. My 2 cents.

Depends. Some don’t deliver any more after 1.5 - 2 turns. Many epa carbs now have a fixed jet that flows 90% of the required fuel and the other 10% happens in the next 4 turns. Redmax and Echo stuff can be like that.

But if you can tune to both a rich and a lean condition, a fixed jet change is only going to get you closer to the center of your adjustment.

 

[NateSaw]

It's been a bunch of pages since I've done it, so it's time again, to break out the box of kleenex and a hallmark card. I'm really glad all you nutballs are in here throwing darts at this project. This is a community project. I may not be using all the ideas thrown this way, but I assure you, I am DEEPLY considering/pondering EVERY. SINGLE. ONE. If anyone trolling this site gets anything out of this, it should be just how badass all you mfkrs are, and although it's prolly too limp wristed for everyone to cuddlefug about it, this site has one of the highest concentrations of decent human beings the world has to offer. Most of you do this as your bread and butter. It is IMPERITIVE that some of you play your cards close to your chest, so some theif doesn't steal all your hard earned realizations... Yet the food for thought, $0.02, breadcrumbs keep comin. And I'm a year old and haven't earned sh#t yet. Alright. Get your balls back. I'm done.

 

[NateSaw]

Depends. Some don’t deliver any more after 1.5 - 2 turns. Many epa carbs now have a fixed jet that flows 90% of the required fuel and the other 10% happens in the next 4 turns. Redmax and Echo stuff can be like that.

But if you can tune to both a rich and a lean condition, a fixed jet change is only going to get you closer to the center of your adjustment.

My 2511. I still can't tune it right. The interdependence is deep.

 

[huskihl]

My 2511. I still can't tune it right. The interdependence is deep.

Bury it in a log. Turn the h out til it 4 strokes. Turn it in until max rpm or it starts acting up lean. Go somewhere in the middle.

Those 2511 carbs are a pos too. Sometimes they need replaced

 

[NateSaw]

Bury it in a log. Turn the h out til it 4 strokes. Turn it in until max rpm or it starts acting up lean. Go somewhere in the middle.

Those 2511 carbs are a pos too. Sometimes they need replaced

THAAAANK YOUUUUU!

 

[NateSaw]

Nate, I'd recommend boring the throttle bore out to fit a bigger throttle plate rather than boring out the venturi. If you leave the throttle bore size stock, and then bore the venturi, you will lose some of the pressure differential that creates the low pressure signal, then the carb will actually draw less fuel. A trick from back in the day was to use the choke plate, in place of the throttle plate, then bore the carb to fit. On the choke side, bore it over the same percentage it was compared to the throttle bore. Make a new choke plate....

Then increase the venturi in a D shape as not to cut into the fuel delivery passage from the pump side.

So I'd be porting it, not turning it. I see.

 

[Rich Fife]

I've had great results with just boring the choke area and not touching the throttle or venturi areas. It's all about high/low pressures and how they help to draw fuel.

 

[Rich Fife]

Just my $.02 but I honestly think that boring the Venturi is gonna be a step backwards.

This! IMO, there are Many other areas to work on first.

 

[Dolkitafreak]

Working around current fueling is a poor train of thought, I’d chase air first, then mod a carb to fuel what I desire…

Modding or large carbs isn’t that a small carb can’t keep up, it’s that a larger or modded carb may allow you to either make more peak power, or move your peak power up and cut faster. Keeping a stock HD on the saw it will be constrained to warm 046 levels imo. Just a hack, take it for what it’s worth