Carburetor talk - fuel puddling

[jacktheripper]

I have been dealing with several similar issues on a few different saws lately. The issue is definitely related to the carburetor on each of these saws. It is provoked by setting a saw down for 15-30 seconds at idle, and then picking it up, which causes the saw to die. The first thought that came to my mind was that it was fuel puddling somewhere in the intake tract due to a lip protruding, and is released into the crankcase when the saw is picked up, causing the saw to die or lose rpms from running rich. This is a common issue on the 026 and 044. However, in my case I found that every one of these issues for me is actually related to the carburetor. How do I know that? Because they go away when a good carb is put on the saw.

I have played with tuning for hours, pop-off pressure, metering lever height, cleaning carbs, kitting carbs, swapping jets, swapping nozzles, and just about everything else in my quest to make the bad carbs run better. I have experienced some success, but not total success, with a couple of them. One of the partial successes involved swapping the nozzle/check valve assy. Another involved raising pop-off by putting a VERY stiff spring under the metering arm.

My question to everyone is: what in the world would cause a carb to load a saw up at idle? Some of these saws are on the ragged edge of lean (almost won’t idle because they’re tuned so lean at idle), but then they still load the intake up. The effect is most pronounced when the saw is tilted downwards quickly.

My theory is that it has something to do with atomization of fuel. Maybe the carb is just simply bad because the jets are worn out and not atomizing. Does this sound reasonable? I’d love to hear your thoughts.

 

[edisto]

Interesting question...and from the sounds of it, I'm not going to say anything that you don't already know/haven't tried.

Letting a saw sit at idle, and then rotating it is a good way to make sure you aren't idling too rich, because fuel puddles in the crankcase. But you are still having the issue when running lean. Inadequate atomization makes sense.

At idle, the throttle valve is mostly closed, and the notch in the valve (or just the restriction) creates a venturi for the 3 tiny holes that terminate the idle circuit. That's where the atomization would be happening. I would assume that any restriction in one of those holes would require the L screw to be turned out to compensate by pushing more fuel through the unrestricted holes, which would affect atomization. But, you've cleaned and kitted (so the Welch plug has come out), so you still are having those issues with the holes unrestricted.

After that atomization, and keeping droplets in suspension, is (to my understanding) a product of the intake itself. Rough walls and the raised diamonds in some intake boots counteract the formation of a boundary layer at the walls, keeping the droplets in suspension. At idle, I think that these mechanics are less effective. I wonder if roughening the carb throat ahead of the idle jets/holes would make a difference?

Apart from restrictions on the idle jets/holes (or the unlikely enlarging of those holes), I haven't mentioned anything that could be fixed by a new carb...which means that I have just wasted your time.

 

[Sloughfoot]

I have been dealing with several similar issues on a few different saws lately. The issue is definitely related to the carburetor on each of these saws. It is provoked by setting a saw down for 15-30 seconds at idle, and then picking it up, which causes the saw to die. The first thought that came to my mind was that it was fuel puddling somewhere in the intake tract due to a lip protruding, and is released into the crankcase when the saw is picked up, causing the saw to die or lose rpms from running rich. This is a common issue on the 026 and 044. However, in my case I found that every one of these issues for me is actually related to the carburetor. How do I know that? Because they go away when a good carb is put on the saw.

I have played with tuning for hours, pop-off pressure, metering lever height, cleaning carbs, kitting carbs, swapping jets, swapping nozzles, and just about everything else in my quest to make the bad carbs run better. I have experienced some success, but not total success, with a couple of them. One of the partial successes involved swapping the nozzle/check valve assy. Another involved raising pop-off by putting a VERY stiff spring under the metering arm.

My question to everyone is: what in the world would cause a carb to load a saw up at idle? Some of these saws are on the ragged edge of lean (almost won’t idle because they’re tuned so lean at idle), but then they still load the intake up. The effect is most pronounced when the saw is tilted downwards quickly.

My theory is that it has something to do with atomization of fuel. Maybe the carb is just simply bad because the jets are worn out and not atomizing. Does this sound reasonable? I’d love to hear your thoughts.

Good question. I've had the same experiences and don't have a fookin clue. I don't buy the flat spot in the manifold theory though.

 

[qurotro]

I've experienced the same thing but it's caused by vibration.. Putting the saw on the ground it vibrate the carb and would idle richer and richer then die. But when I hold the saw idling it can idle all day.

 

[Stump Shot]

I have been dealing with several similar issues on a few different saws lately. The issue is definitely related to the carburetor on each of these saws. It is provoked by setting a saw down for 15-30 seconds at idle, and then picking it up, which causes the saw to die. The first thought that came to my mind was that it was fuel puddling somewhere in the intake tract due to a lip protruding, and is released into the crankcase when the saw is picked up, causing the saw to die or lose rpms from running rich. This is a common issue on the 026 and 044. However, in my case I found that every one of these issues for me is actually related to the carburetor. How do I know that? Because they go away when a good carb is put on the saw.

I have played with tuning for hours, pop-off pressure, metering lever height, cleaning carbs, kitting carbs, swapping jets, swapping nozzles, and just about everything else in my quest to make the bad carbs run better. I have experienced some success, but not total success, with a couple of them. One of the partial successes involved swapping the nozzle/check valve assy. Another involved raising pop-off by putting a VERY stiff spring under the metering arm.

My question to everyone is: what in the world would cause a carb to load a saw up at idle? Some of these saws are on the ragged edge of lean (almost won’t idle because they’re tuned so lean at idle), but then they still load the intake up. The effect is most pronounced when the saw is tilted downwards quickly.

My theory is that it has something to do with atomization of fuel. Maybe the carb is just simply bad because the jets are worn out and not atomizing. Does this sound reasonable? I’d love to hear your thoughts.

I have a theory, because the carburetor is set so lean at idle, the throttle plate is therefor closed too tight/much to compensate for idle speed. So, it just could be possible if you give it more fuel and hence more AIR it could cure your issue maybe.

 

[hacskaroly]

It is provoked by setting a saw down for 15-30 seconds at idle, and then picking it up, which causes the saw to die.

Just out of curiosity, I wonder if there is any difference if you blip the trigger a couple of times before picking it up, if it would still do the same thing or if there is any "pooling" fuel that might get cleared out during the quick blips.

 

[jacktheripper]

Just out of curiosity, I wonder if there is any difference if you blip the trigger a couple of times before picking it up, if it would still do the same thing or if there is any "pooling" fuel that might get cleared out during the quick blips.

That is actually what I have been doing on a couple of saws in order to pick them up. The blips do work, and you can tell that it’s eating fuel when you do it.

 

[Sloughfoot]

Problem with the one I have that does this is that the tune that holds idle when you pick it up doesn't accelerate well and the tune that accelerates well doesn't hold idle when you pick it up. More H for less L and vice versa don't seem to help. Highest it will idle and stay off the clutch is good as it gets.

 

[mainer_in_ak]

It is winter time and im surprised nobody hasn't mentioned the issues that come from cold weather ops. All Carburetors like warm air. There are over 2 dozen carburetors on various pieces of equipment around my homestead. They all get finicky in this constant 20-30 below zero weather.

I wonder if u couldn't richen your low jet, bring up yer idle to where the point where yer clutch "almost" engages.

Also, try to make certain yer winter setting is on, if the saw has one. Sometimes some extra heat on the carb helps immensely. Sometimes ill add a port to the engine cover to bring more heat to the carb. And also tape off the bottom third of my flywheel vents.

Here's one that needed more heat to the carb 3 hoses off the engine cover:

 

[Ketchup]

Have you altered the intake duration? Do you get spitback out the carb?

 

[jacktheripper]

Have you altered the intake duration? Do you get spitback out the carb?

No spitback, two of the saws were very much altered, but professionally by @drf256 and @Mastermind and the issues go away with different carbs

 

[Sloughfoot]

The one I had that was doing it decided to stop putting fuel in the venturi completely. Plenty of fuel on the pump and metering side, none in the saw. Would start on a prime and die immediately. Probably unrelated, maybe not. Replaced it with an aftermarket I had on hand and it runs great. Go figure.

Kinda remember bending the metering lever down on this AM carb awhile back. Don't remember if it was high or I just thought it might run better lower. Maybe a high metering lever loads up the carb or case when idling, somehow.

 

[singinwoodwackr]

It is winter time and im surprised nobody hasn't mentioned the issues that come from cold weather ops. All Carburetors like warm air. There are over 2 dozen carburetors on various pieces of equipment around my homestead. They all get finicky in this constant 20-30 below zero weather.

I wonder if u couldn't richen your low jet, bring up yer idle to where the point where yer clutch "almost" engages.

Also, try to make certain yer winter setting is on, if the saw has one. Sometimes some extra heat on the carb helps immensely. Sometimes ill add a port to the engine cover to bring more heat to the carb. And also tape off the bottom third of my flywheel vents.

Here's one that needed more heat to the carb 3 hoses off the engine cover:

View attachment 477127

I’d move..

 

[Sloughfoot]

Have you altered the intake duration? Do you get spitback out the carb?

No spitback, two of the saws were very much altered, but professionally by @drf256 and @Mastermind and the issues go away with different carbs

Altered is an ugly word.

 

[Wonkydonkey]

I’ve found laying the saw on its side (clutch side down) stops the saw from dying compared to putting the saw down normally.

Has anyone else noticed this ?

I’ve tried to figure out why it seems help my 260

I wonder if it’s a specific of the problem of a model of carb/s ?

As for the butterfly being almost closed, I remember there was a carb bulletin? (Can’t remember for which saw or carb) but the difference was the butterfly had two notches ? I will have to have a dig around and see if I can find this info and as to what carb it was on and if it relates to the problem we have ?


I'll follow this interesting thread

 

[Sloughfoot]

,

 

[Junk Meister]

I would be vigilant on a 026/260 for a seal to leak, laying the saw on its side allows the crank to shift and maybe snug up any loose fits. Many threads on tip testing. The flywheel side tends to be the 1st to fail. It has been a while since I read any on the topic.

 

[Poleman]

What I’ve found that helps me is on the line of what Stump Shot said. Throttle closed restricting air through carb slowing mix down and dropping out causing the puddling. My fix for that is to drill a small hole in the throttle plate to let more air through and speed up velocity so there is no drop out. How big… depends on how bad it is. Bad a bigger hole than just a little bit. Why I drill a hole if you go to much and can’t control idle then you went to big… spiller it shut and go small than what last hole drilled was.
This is what I’ve found that works for me on carbs that have issues like your describing. Works on ported saws also when more air is needed.
Easy to fix if it doesn’t work other than notching the plate.

 

[edisto]

My fix for that is to drill a small hole in the throttle plate to let more air through and speed up velocity so there is no drop out.

A bigger opening or an additional opening would decrease velocity, but it might be creating some currents that keep the fuel suspended.

 

[jacob j.]

What I’ve found that helps me is on the line of what Stump Shot said. Throttle closed restricting air through carb slowing mix down and dropping out causing the puddling. My fix for that is to drill a small hole in the throttle plate to let more air through and speed up velocity so there is no drop out. How big… depends on how bad it is. Bad a bigger hole than just a little bit. Why I drill a hole if you go to much and can’t control idle then you went to big… spiller it shut and go small than what last hole drilled was.
This is what I’ve found that works for me on carbs that have issues like your describing. Works on ported saws also when more air is needed.
Easy to fix if it doesn’t work other than notching the plate.

Years ago (mid 1990's) I had an 026 that was having issues at idle - a local long-time small engine tech told me to notch the throttle plate in front of where there was a secondary opening in the throttle bore part of the carburetor. I notched it about 1/16" (roughly doubling the size of the small existing notch). My idle problems went away and the saw ran great.