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New Super Recycler sputtering issue.
#2
Scrubcadet10
Scrubcadet10
#4
gotomow
gotomow
#7
gotomow
gotomow
#17
P
POM
Been looking into which B&S engines use the 596505 carburetor and from an on-line parts store catalog found an "applicable to" list (these are B&S engine model numbers):
104M02-0130-F1
104M02-0131-F1
104M02-0249-F1
104M02-0254-F1
I then verified on the B&S site that these engine models do indeed use the 596505 carb.
In my searching I also came across mention of the carburetor being replaced by dealers according to a bulletin to fix the sputtering problem, but the context was the Toro 21387, which has the 190 cc engine. I suspect that DSB-113/DBS-114 might apply to that engine and not the 163 cc with the 596505 carb. In this regard, Toro seems to have only four "SmartStow" models that use the 163 cc. engine: 20339, 20340, 20355, and 21386, and interestingly, reviews of these models on the Toro website also mention the sputtering issue. I haven't yet found whether the 190 cc engine on the SmartStow 21387 uses the same carburetor, although I doubt it does. But the bulletin might explain what the problem is with the carburetor and that might also be applicable to the 596505. as both would be set up for vertical storage.
According to this B&S YouTube video the Mow and Stow/SmartStow engines incorporate a number of changes:
,
Only two would seem to possibly be related to the sputtering issue, namely, the revised carburetor vent, and the revised governor shaft. The video shows an older, metal carb, and refers only to changing the position of one vent. However, when I compare the plastic 596505 carb to plastic carbs used on non-SmartStow models, there's several vents that are different. This is what led me to think that the sputtering is related to the different carb. And if changing the carb on the 21387 fixed sputtering, the same change to a different carburetor might fix the problem some of us have with the 163 cc engine. As for the governor, I'm not aware of any internal changes that could affect governor operation in a way that bumps would cause the governor mechanism inside to initiate a momentary throttle change.
This B&S video is a good explanation of carburetors especially because it uses the plastic one as the model:
However, the venting in the 596505 is not the same. One visually obvious difference is the bowl area vent outlet. Instead of being terminated at a simple round plug (the "baffle") in the video at around 10:15, the 596505 has a horizontal extension tube. (See photos below). This extension, I presume, is designed to prevent fuel in the bowl from spilling out through the atmospheric vent when the engine is raised in the Stow position. But I suspect that when operating on uneven surfaces, the "sloshing" fuel in the bowl might enter this short, horizontal tube, restricting or blocking the tube, and as the video notes around 10:20, when the vent is blocked, "fuel is supplied to the engine for a very short time". So, momentarily, the engine is starved, and hesitates. The governor opens the throttle, and when the vent clears, the engine fuel supply suddenly surges, leading not only to recovery but also a puff of dark smoke due to the brief "rich" fuel mix. It's only an idea, until I learn otherwise . . .
P
POM
B&S had/has a large number of 7.25, 163 cc., engines, but they are not all the same.
Been looking into which B&S engines use the 596505 carburetor and from an on-line parts store catalog found an "applicable to" list (these are B&S engine model numbers):
104M02-0130-F1
104M02-0131-F1
104M02-0249-F1
104M02-0254-F1
I then verified on the B&S site that these engine models do indeed use the 596505 carb.
In my searching I also came across mention of the carburetor being replaced by dealers according to a bulletin to fix the sputtering problem, but the context was the Toro 21387, which has the 190 cc engine. I suspect that DSB-113/DBS-114 might apply to that engine and not the 163 cc with the 596505 carb. In this regard, Toro seems to have only four "SmartStow" models that use the 163 cc. engine: 20339, 20340, 20355, and 21386, and interestingly, reviews of these models on the Toro website also mention the sputtering issue. I haven't yet found whether the 190 cc engine on the SmartStow 21387 uses the same carburetor, although I doubt it does. But the bulletin might explain what the problem is with the carburetor and that might also be applicable to the 596505. as both would be set up for vertical storage.
According to this B&S YouTube video the Mow and Stow/SmartStow engines incorporate a number of changes:
Only two would seem to possibly be related to the sputtering issue, namely, the revised carburetor vent, and the revised governor shaft. The video shows an older, metal carb, and refers only to changing the position of one vent. However, when I compare the plastic 596505 carb to plastic carbs used on non-SmartStow models, there's several vents that are different. This is what led me to think that the sputtering is related to the different carb. And if changing the carb on the 21387 fixed sputtering, the same change to a different carburetor might fix the problem some of us have with the 163 cc engine. As for the governor, I'm not aware of any internal changes that could affect governor operation in a way that bumps would cause the governor mechanism inside to initiate a momentary throttle change.
This B&S video is a good explanation of carburetors especially because it uses the plastic one as the model:
However, the venting in the 596505 is not the same. One visually obvious difference is the bowl area vent outlet. Instead of being terminated at a simple round plug (the "baffle") in the video at around 10:15, the 596505 has a horizontal extension tube. (See photos below). This extension, I presume, is designed to prevent fuel in the bowl from spilling out through the atmospheric vent when the engine is raised in the Stow position. But I suspect that when operating on uneven surfaces, the "sloshing" fuel in the bowl might enter this short, horizontal tube, restricting or blocking the tube, and as the video notes around 10:20, when the vent is blocked, "fuel is supplied to the engine for a very short time". So, momentarily, the engine is starved, and hesitates. The governor opens the throttle, and when the vent clears, the engine fuel supply suddenly surges, leading not only to recovery but also a puff of dark smoke due to the brief "rich" fuel mix. It's only an idea, until I learn otherwise . . .
#19
P
POM
P
POM
Further info:
In regard to the venting, the B&S video points out that the fuel bowl vent is to atmosphere. That is correct for a non-SmartStow carburetor I have (799584). However, the SmartStow 596505 is different. Here's a comparison:
In the Normal configuration, both the "low speed air supply" and the "air mix for main jet" openings are after the air filter, with the "low speed air supply" also being after the choke. Both go to their intended locations inside the carburetor. As is apparent, the "fuel bowl vent" is separated from the carburetor inlet by the gasket, and actually opens out to atmosphere behind the air filter housing.
In the SmartStow 596505 carb, I found the "low speed air supply" and the "fuel bowl vent" passages to be closed internally, i.e., they don't go anywhere. (I could not see the low speed jet openings in the side of the venturi tubes in both carbs so that vent might not be needed.) Although the passage for the "air mix for the main jet" is the same as in the Normal configuration, in the 596505 it's also connected to passage going to the extended "fuel bowl vent" inside the fuel bowl. In other words, the fuel bowl venting in the 596505 does not originate out in atmosphere; it's after the filter.
Odd difference in the fuel bowl venting. Seems to me it would be affected by the throttle opening and the condition of the air filter. Could this be related to the sputtering that occurs when going over rough areas in the lawn?
In regard to the venting, the B&S video points out that the fuel bowl vent is to atmosphere. That is correct for a non-SmartStow carburetor I have (799584). However, the SmartStow 596505 is different. Here's a comparison:
In the Normal configuration, both the "low speed air supply" and the "air mix for main jet" openings are after the air filter, with the "low speed air supply" also being after the choke. Both go to their intended locations inside the carburetor. As is apparent, the "fuel bowl vent" is separated from the carburetor inlet by the gasket, and actually opens out to atmosphere behind the air filter housing.
In the SmartStow 596505 carb, I found the "low speed air supply" and the "fuel bowl vent" passages to be closed internally, i.e., they don't go anywhere. (I could not see the low speed jet openings in the side of the venturi tubes in both carbs so that vent might not be needed.) Although the passage for the "air mix for the main jet" is the same as in the Normal configuration, in the 596505 it's also connected to passage going to the extended "fuel bowl vent" inside the fuel bowl. In other words, the fuel bowl venting in the 596505 does not originate out in atmosphere; it's after the filter.
Odd difference in the fuel bowl venting. Seems to me it would be affected by the throttle opening and the condition of the air filter. Could this be related to the sputtering that occurs when going over rough areas in the lawn?
#27
P
POM
P
POM
Continuing . . .
It's my belief that the horizontal extension of the SmartStow baffle is meant to ensure that when the mower is in the vertical position, the fuel in the bowl can't leak out the vent because the opening will be above the level of the fuel. But, as noted earlier, I put my mower with the modified vent in the SmartStow position and left it for several hours and there was no sign of leakage, despite not having the extended baffle.
Did some bench testing. I clamped the spare non-SmartStow carb I have (799584) on a camera tripod so that it can be set horizontal (normal run position) and vertical (stow position).
With a short clear vinyl tube attached to the fuel inlet, I flowed distilled water into the bowl until it would not take any more. This is simulating the fuel tank supply, and the inlet valve closing when the float gets high enough.
I then closed off the end of the vinyl tube, rotated the tripod mount 90 degrees, as in the vertical SmartStow position, and waited. There was no sign of leaking, even after several hours.
When the carb is vertical, the fuel inlet is the lowest passage going outside; next lowest is the atmospheric vent (with the flat, circular "baffle"); and, above that is the main nozzle jet with it's tiny opening.
I don't know at what level the water would be in the bowl when the bowl is vertical, but imagine it's at least as high as the atmospheric vent, and would not have been surprised to see water coming out from that vent. I even rotated the carb another 45 degrees (almost up-side-down) and again expected water to come out of the atmospheric vent, but it didn't. The only rationale I can offer for it not leaking is that the water level is above the atmospheric vent opening, and with no other large path for air to get into the bowl, the water doesn't go out the vent.
With the carb in the vertical position, I then pulled the plug off the end of the short vinyl tube; water flowed out, but in this case it's coming back out through the tube that is normally attached to the fuel tank, so that would not be a problem. (In this case, the weight of the water trying to go out what is then the bottom of the bowl area is sufficient to allow atmospheric pressure at the vent to push water back from the vent baffle and supply the air needed to compensate for the water going out the fuel tank fitting.
From this it suggests that both the SmartStow and regular current black plastic carbs of the same design might normally (when all is working properly) drain back into the fuel tank when lifted into the vertical position, reducing if not eliminating the possibility of leaks.
However, if for some reason the bowl doesn't drain down into the fuel tank e.g., inlet valve remains closed, in the longer term liquid could seep out through the atmospheric vent if the liquid is higher than the vent. This could happen because the main jet, albeit a very small opening, terminates in carburetor's venturi air passage. Consequently, air could be drawn into the bowl area very slowly through the main jet and allow liquid to leak out the vent.
In the SmartStow carbs, the extended vent baffle opening is above the liquid level, and there's no risk of liquid/fuel leaking out that path when air finds its way into the bowl area.
The problem for B&S is how to correct the issue of the atmospheric vent being blocked by fuel when operating (my understanding of the cause of the sputtering), while ensuring that leakage in storage can't happen. Looking at the innards of the carbs and the current passages for fuel and venting, I think it could require a significant change in the design of the upper half of the carburetor.
As an interim measure **, if the mower will be stored in the vertical position, to protect against the possibility of leakage if the bowl does not drain back to the fuel tank, a fuel shut-off valve could be added to cut the fuel supply and then run the engine until it stalls. At that time, there will be little fuel left in the bowl, and the risk of fuel exiting through the atmospheric vent because the bowl didn't drain back to the fuel tank when the mower was lifted would be low.
That's the way I see it at this point, but do I have it right? Comments, further ideas etc., encouraged and welcome.
**We know from user reports that B&S has successfully addressed the sputtering problem in at least some 190 cc SmartStow engines used by Toro, so there is a fix that, presumably, retains the SmartStow function. Goal now is to find out what that fix is, and see if it can be applied to the 163 cc SmartStow engine.
Update July 18, 2021: FWIW I ran multiple "fill - drain" tests, and every time found the bowl would self-drain when the carb is lifted from horizontal to the vertical/stow position. It took about 28 ml to fill a completely empty carburetor. In the vertical position, 20 ml drained back out the inlet tube. With the carb vertical, the remaining 8 ml is at the level of the lower edge of the large hex drain opening in the bottom part of the bowl, and at the level of the inlet valve, so well below any other paths for fuel to leak out when in the vertical position.
It's my belief that the horizontal extension of the SmartStow baffle is meant to ensure that when the mower is in the vertical position, the fuel in the bowl can't leak out the vent because the opening will be above the level of the fuel. But, as noted earlier, I put my mower with the modified vent in the SmartStow position and left it for several hours and there was no sign of leakage, despite not having the extended baffle.
I had thought that as well. But your substitution of the 594098, which is for the 163 cc but not SmartStow, seems to be a viable solution, with precautions as described below.
Did some bench testing. I clamped the spare non-SmartStow carb I have (799584) on a camera tripod so that it can be set horizontal (normal run position) and vertical (stow position).
With a short clear vinyl tube attached to the fuel inlet, I flowed distilled water into the bowl until it would not take any more. This is simulating the fuel tank supply, and the inlet valve closing when the float gets high enough.
I then closed off the end of the vinyl tube, rotated the tripod mount 90 degrees, as in the vertical SmartStow position, and waited. There was no sign of leaking, even after several hours.
When the carb is vertical, the fuel inlet is the lowest passage going outside; next lowest is the atmospheric vent (with the flat, circular "baffle"); and, above that is the main nozzle jet with it's tiny opening.
I don't know at what level the water would be in the bowl when the bowl is vertical, but imagine it's at least as high as the atmospheric vent, and would not have been surprised to see water coming out from that vent. I even rotated the carb another 45 degrees (almost up-side-down) and again expected water to come out of the atmospheric vent, but it didn't. The only rationale I can offer for it not leaking is that the water level is above the atmospheric vent opening, and with no other large path for air to get into the bowl, the water doesn't go out the vent.
With the carb in the vertical position, I then pulled the plug off the end of the short vinyl tube; water flowed out, but in this case it's coming back out through the tube that is normally attached to the fuel tank, so that would not be a problem. (In this case, the weight of the water trying to go out what is then the bottom of the bowl area is sufficient to allow atmospheric pressure at the vent to push water back from the vent baffle and supply the air needed to compensate for the water going out the fuel tank fitting.
From this it suggests that both the SmartStow and regular current black plastic carbs of the same design might normally (when all is working properly) drain back into the fuel tank when lifted into the vertical position, reducing if not eliminating the possibility of leaks.
However, if for some reason the bowl doesn't drain down into the fuel tank e.g., inlet valve remains closed, in the longer term liquid could seep out through the atmospheric vent if the liquid is higher than the vent. This could happen because the main jet, albeit a very small opening, terminates in carburetor's venturi air passage. Consequently, air could be drawn into the bowl area very slowly through the main jet and allow liquid to leak out the vent.
In the SmartStow carbs, the extended vent baffle opening is above the liquid level, and there's no risk of liquid/fuel leaking out that path when air finds its way into the bowl area.
The problem for B&S is how to correct the issue of the atmospheric vent being blocked by fuel when operating (my understanding of the cause of the sputtering), while ensuring that leakage in storage can't happen. Looking at the innards of the carbs and the current passages for fuel and venting, I think it could require a significant change in the design of the upper half of the carburetor.
As an interim measure **, if the mower will be stored in the vertical position, to protect against the possibility of leakage if the bowl does not drain back to the fuel tank, a fuel shut-off valve could be added to cut the fuel supply and then run the engine until it stalls. At that time, there will be little fuel left in the bowl, and the risk of fuel exiting through the atmospheric vent because the bowl didn't drain back to the fuel tank when the mower was lifted would be low.
That's the way I see it at this point, but do I have it right? Comments, further ideas etc., encouraged and welcome.
**We know from user reports that B&S has successfully addressed the sputtering problem in at least some 190 cc SmartStow engines used by Toro, so there is a fix that, presumably, retains the SmartStow function. Goal now is to find out what that fix is, and see if it can be applied to the 163 cc SmartStow engine.
Update July 18, 2021: FWIW I ran multiple "fill - drain" tests, and every time found the bowl would self-drain when the carb is lifted from horizontal to the vertical/stow position. It took about 28 ml to fill a completely empty carburetor. In the vertical position, 20 ml drained back out the inlet tube. With the carb vertical, the remaining 8 ml is at the level of the lower edge of the large hex drain opening in the bottom part of the bowl, and at the level of the inlet valve, so well below any other paths for fuel to leak out when in the vertical position.
#28
wingless
wingless
#30
wingless
wingless