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Tor R

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Far as I know (just by study IPL), I can't see any mayor difference else then heathed and EPA when it goes to 190,191,199,199?

Else then all those 199 i have, I have also one old walbro, anyone knows difference from 174 to 198?
 

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I know this is an old thread, and there are posts all over asking these questions. But I just wanted to share some information, in case it is useful to anyone in the future.

1. The 357XP and 359 were introduced in 2001. Depending on the locale where they were sold, they either came with a Walbro HDA-174 or an EPA regulated Walbro HDA-175. The differences between these two carbs will become clear as an emerging pattern, as Walbro provides the 174 as a normal carb with a 16.66mm venturi, and the 175 as an EPA compliant carb. The major difference was the 175 had smaller jets, so to achieve faster acceleration it had a built in accelerator pump. Since the accelerator pump is such a crucial difference, it may be useful to understand what it is and does.

The accelerator pump is responsible for providing the momentary additional fuel needed under heavy acceleration conditions. When the trigger or pedal is pressed, the throttle suddenly opens, immediately adding additional air for additional power. That additional air requires additional fuel, especially in the precise moments after the throttle is opened, this is the fuel the accelerator pump provides. When the throttle is rapidly opened, the accelerator pump will squirt a small amount of fuel into the throat of the carburetor so that the engine can continue running smoothly under increased load. Usually when the accelerator pump is having issues, it will display a few symptoms that can alert the operator that there may be a problem that should be inspected.

Rough acceleration
One of the most common symptoms that the accelerator pump is having a problem is rough or sluggish acceleration. The accelerator pump is supposed to provide additional fuel needed during acceleration. If there is any problem with the pump, then there will be a problem in the fuel mixture during acceleration. Usually, a faulty accelerator pump will result in a momentary lean condition, which can result in rough or sluggish acceleration, and even misfires.

Engine sputtering or stalling
Another symptom of a faulty accelerator pump is engine sputtering or stalling. The sputtering is caused by the lack of fuel that is supposed to be provided by the accelerator pump when throttle is rapidly pressed. In more serious cases of accelerator pump failure, rapidly pressing on the gas may cause the engine to stall, again due to the lean condition that can be created when the accelerator pump is not working.

A faulty accelerator pump will typically produce a noticeable effect on the engine performance when it fails or is having a problem. If you suspect that your accelerator pump may be having an issue, have the carburetor diagnosed by a professional technician.

The HDA-175 also had adjustment needles with limiters and a different metering spring providing different pop-off pressure.
Screen Shot 2018-10-01 at 7.26.36 PM.png
Around 2004 the HDA-174 and HDA-175 were discontinued by Walbro, forcing Husqvarna to select new carbs for their product.
Screen Shot 2018-10-01 at 7.31.01 PM.png

2. In April 2003 Husqvarna updated their 357XP and 359 to use 4 new carbs! All four carbs still use a 16.66mm venturi. The particular carb choice is dependent on two qualifications: the first is if the saw came with handle heating (357XPG and 359G) or without handle heating (357XP and 359), and the second qualification is if the saw was sold in a locale requiring EPA regulation compliance, or not. Saws with handle heating received a Walbro HDA-190A, or a Walbro HDA-191A if they needed to meet EPA regulations. Saws without handle heating received a Walbro HDA-198A, or a Walbro HDA-199A if they needed to meet EPA regulations. Again, the major differences between the non-EPA and the EPA carbs are the restriction of jet size, adjustment needles with limiters and an accelerator pump.

The major difference between the heated handle carbs (190 and 191) and the non-heated handle carbs (198 and 199) was the inclusion of a plastic ring (537 04 53-01) at the top of the carb on non-heated handle carbs. This was Walbro's version of a compensating carburetor, similar to Stihl's Intellicarb idea. The principle was there was a passageway which allowed the backside of the metering diaphragm to have access to the pressure inside the intake track, after the air filter. The concept was that as the air filter gets clogged up, a more negative pressure develops and more fuel would be sucked through the carb without as much air, resulting in a rich condition. To compensate, the negative pressure was added to the top side of the metering diaphragm to counter-act the pressure difference. Scott Kunz (@Treemonkey) believes this to be a poor design, because the passage way is small. He tends to solve problems with HDA-199 carbs by making them like 191 carbs. The 191 carbs do not have a plastic ring at the top of the carb, because the ring thermally decoupled the top cover where the carb heater sat. Therefore, on heated handle (and carb) saws, the 190/191 carb was used, without a ring, and with a simple hole drilled in the top cover, and no compensation.

This is best explained in this Service Bulletin.

After 2005, EU regulations meant saws sold there received the EPA version carbs.
Screen Shot 2018-10-01 at 7.24.03 PM.png
Walbro has never provided instructions or parts to service the accelerator pump. Whether due to fuel quality or simply a limited lifetime, the accelerator pump would often get gummed up and stick, causing running problems. The easy fix was to replace the whole carb, as most small-engine technicians were not going to go through the trouble to diagnose, remove, service, and replace an accelerator pump.

3. In October 2008 Husqvarna introduced a service bulletin to change the carb on the 357XP and 359 again, this time to the Zama C3-EL42, ostensibly for better idling stability.


Regarding the use of these carbs on 346XP saws.

Any of these Walbro carbs will be a direct swap into a 346XP, however, little gain would be seen on a stock saw, while only modest gain might be seen on a gasket delete/muffler mod. To take advantage of the larger gains possible with these carbs would require full port jobs to a cylinder. Of all the carb choices, I would suggest given the choice between two carbs that the non-EPA, non accelerator pump carbs would be preferable. That means an HDA-174, HDA-190, or HDA-198. These carbs are, however, more rare, since less saws were produced with them. There is nothing wrong with using an EPA carb from a 357XP/359, although they too are becoming harder to find. The only downside is that the additional complication of the accelerator pump may mean they have a shorter service life due to a possible failure of the accelerator pump. I am also not certain if the possibility for failure of the accelerator pump would outweigh its benefit for a ported saw. It may be that the accelerator pump version carb performs better? Only side-by-side testing would show that.

The EL-42 carb will also work for a 346XP upgrade, however, it may not deliver enough fuel to a ported saw. There is a modification that can be made to drill out the jet, which is detailed here, to increase fuel delivery.
 
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I know this is an old thread, and there are posts all over asking these questions. But I just wanted to share some information, in case it is useful to anyone in the future.

1. The 357XP and 359 were introduced in 2001. Depending on the locale where they were sold, they either came with a Walbro HDA-174 or an EPA regulated Walbro HDA-175. The differences between these two carbs will become clear as an emerging pattern, as Walbro provides the 174 as a normal carb with a 16.66mm venturi, and the 175 as an EPA compliant carb. The major difference was the 175 had smaller jets, so to achieve faster acceleration it had a built in accelerator pump. Since the accelerator pump is such a crucial difference, it may be useful to understand what it is and does.



The HDA-175 also had adjustment needles with limiters and a different metering spring providing different pop-off pressure.
View attachment 143841
Around 2004 the HDA-174 and HDA-175 were discontinued by Walbro, forcing Husqvarna to select new carbs for their product.
View attachment 143842

2. In April 2003 Husqvarna updated their 357XP and 359 to use 4 new carbs! All four carbs still use a 16.66mm venturi. The particular carb choice is dependent on two qualifications: the first is if the saw came with handle heating (357XPG and 359G) or without handle heating (357XP and 359), and the second qualification is if the saw was sold in a locale requiring EPA regulation compliance, or not. Saws with handle heating received a Walbro HDA-190A, or a Walbro HDA-191A if they needed to meet EPA regulations. Saws without handle heating received a Walbro HDA-198A, or a Walbro HDA-199A if they needed to meet EPA regulations. Again, the major differences between the non-EPA and the EPA carbs are the restriction of jet size, adjustment needles with limiters and an accelerator pump.

The major difference between the heated handle carbs (190 and 191) and the non-heated handle carbs (198 and 199) was the inclusion of a plastic ring (537 04 53-01) at the top of the carb on non-heated handle carbs. This was Walbro's version of a compensating carburetor, similar to Stihl's Intellicarb idea. The principle was there was a passageway which allowed the backside of the metering diaphragm to have access to the pressure inside the intake track, after the air filter. The concept was that as the air filter gets clogged up, a more negative pressure develops and more fuel would be sucked through the carb without as much air, resulting in a rich condition. To compensate, the negative pressure was added to the top side of the metering diaphragm to counter-act the pressure difference. Scott Kunz (@Treemonkey) believes this to be a poor design, because the passage way is small. He tends to solve problems with HDA-199 carbs by making them like 191 carbs. The 191 carbs do not have a plastic ring at the top of the carb, because the ring thermally decoupled the top cover where the carb heater sat. Therefore, on heated handle (and carb) saws, the 190/191 carb was used, without a ring, and with a simple hole drilled in the top cover, and no compensation.

After 2005, EU regulations meant saws sold there received the EPA version carbs.
View attachment 143844
Walbro has never provided instructions or parts to service the accelerator pump. Whether due to fuel quality or simply a limited lifetime, the accelerator pump would often get gummed up and stick, causing running problems. The easy fix was to replace the whole carb, as most small-engine technicians were not going to go through the trouble to diagnose, remove, service, and replace an accelerator pump.

3. In October 2008 Husqvarna introduced a service bulletin to change the carb on the 357XP and 359 again, this time to the Zama C3-EL42, ostensibly for better idling stability.


Regarding the use of these carbs on 346XP saws.

Any of these Walbro carbs will be a direct swap into a 346XP, however, little gain would be seen on a stock saw, while only modest gain might be seen on a gasket delete/muffler mod. To take advantage of the larger gains possible with these carbs would require full port jobs to a cylinder. Of all the carb choices, I would suggest given the choice between two carbs that the non-EPA, non accelerator pump carbs would be preferable. That means an HDA-174, HDA-190, or HDA-198. These carbs are, however, more rare, since less saws were produced with them. There is nothing wrong with using an EPA carb from a 357XP/359, although they too are becoming harder to find. The only downside is that the additional complication of the accelerator pump may mean they have a shorter service life due to a possible failure of the accelerator pump. I am also not certain if the possibility for failure of the accelerator pump would outweigh its benefit for a ported saw. It may be that the accelerator pump version carb performs better? Only side-by-side testing would show that.

The EL-42 carb will also work for a 346XP upgrade, however, it may not deliver enough fuel to a ported saw. There is a modification that can be made to drill out the jet, which is detailed here, to increase fuel delivery.

Thanks. This answered a lot of my "wth were they thinking" moments.
 

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I know this is an old thread, and there are posts all over asking these questions. But I just wanted to share some information, in case it is useful to anyone in the future.

1. The 357XP and 359 were introduced in 2001. Depending on the locale where they were sold, they either came with a Walbro HDA-174 or an EPA regulated Walbro HDA-175. The differences between these two carbs will become clear as an emerging pattern, as Walbro provides the 174 as a normal carb with a 16.66mm venturi, and the 175 as an EPA compliant carb. The major difference was the 175 had smaller jets, so to achieve faster acceleration it had a built in accelerator pump. Since the accelerator pump is such a crucial difference, it may be useful to understand what it is and does.



The HDA-175 also had adjustment needles with limiters and a different metering spring providing different pop-off pressure.
View attachment 143841
Around 2004 the HDA-174 and HDA-175 were discontinued by Walbro, forcing Husqvarna to select new carbs for their product.
View attachment 143842

2. In April 2003 Husqvarna updated their 357XP and 359 to use 4 new carbs! All four carbs still use a 16.66mm venturi. The particular carb choice is dependent on two qualifications: the first is if the saw came with handle heating (357XPG and 359G) or without handle heating (357XP and 359), and the second qualification is if the saw was sold in a locale requiring EPA regulation compliance, or not. Saws with handle heating received a Walbro HDA-190A, or a Walbro HDA-191A if they needed to meet EPA regulations. Saws without handle heating received a Walbro HDA-198A, or a Walbro HDA-199A if they needed to meet EPA regulations. Again, the major differences between the non-EPA and the EPA carbs are the restriction of jet size, adjustment needles with limiters and an accelerator pump.

The major difference between the heated handle carbs (190 and 191) and the non-heated handle carbs (198 and 199) was the inclusion of a plastic ring (537 04 53-01) at the top of the carb on non-heated handle carbs. This was Walbro's version of a compensating carburetor, similar to Stihl's Intellicarb idea. The principle was there was a passageway which allowed the backside of the metering diaphragm to have access to the pressure inside the intake track, after the air filter. The concept was that as the air filter gets clogged up, a more negative pressure develops and more fuel would be sucked through the carb without as much air, resulting in a rich condition. To compensate, the negative pressure was added to the top side of the metering diaphragm to counter-act the pressure difference. Scott Kunz (@Treemonkey) believes this to be a poor design, because the passage way is small. He tends to solve problems with HDA-199 carbs by making them like 191 carbs. The 191 carbs do not have a plastic ring at the top of the carb, because the ring thermally decoupled the top cover where the carb heater sat. Therefore, on heated handle (and carb) saws, the 190/191 carb was used, without a ring, and with a simple hole drilled in the top cover, and no compensation.

After 2005, EU regulations meant saws sold there received the EPA version carbs.
View attachment 143844
Walbro has never provided instructions or parts to service the accelerator pump. Whether due to fuel quality or simply a limited lifetime, the accelerator pump would often get gummed up and stick, causing running problems. The easy fix was to replace the whole carb, as most small-engine technicians were not going to go through the trouble to diagnose, remove, service, and replace an accelerator pump.

3. In October 2008 Husqvarna introduced a service bulletin to change the carb on the 357XP and 359 again, this time to the Zama C3-EL42, ostensibly for better idling stability.


Regarding the use of these carbs on 346XP saws.

Any of these Walbro carbs will be a direct swap into a 346XP, however, little gain would be seen on a stock saw, while only modest gain might be seen on a gasket delete/muffler mod. To take advantage of the larger gains possible with these carbs would require full port jobs to a cylinder. Of all the carb choices, I would suggest given the choice between two carbs that the non-EPA, non accelerator pump carbs would be preferable. That means an HDA-174, HDA-190, or HDA-198. These carbs are, however, more rare, since less saws were produced with them. There is nothing wrong with using an EPA carb from a 357XP/359, although they too are becoming harder to find. The only downside is that the additional complication of the accelerator pump may mean they have a shorter service life due to a possible failure of the accelerator pump. I am also not certain if the possibility for failure of the accelerator pump would outweigh its benefit for a ported saw. It may be that the accelerator pump version carb performs better? Only side-by-side testing would show that.

The EL-42 carb will also work for a 346XP upgrade, however, it may not deliver enough fuel to a ported saw. There is a modification that can be made to drill out the jet, which is detailed here, to increase fuel delivery.
The 199 has always been the hot rod carb for the 346’s I’ve been told
 

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I finally bought a 199 that works great. I’ve sold many that I just couldn’t get to run well even after following the rebuild video. They really made me question my sanity.

However, I really like the Zama el42 on my 346 and my 357. They’re like $32 new. I’d like to yank this 199 on my 357/359 and try it on my T4driller 346 and 357 just to see if there’s a difference.
 

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surprises with jet size: (I bought them in for some time ago since I was currious )
HDA 154 (350), # 537 07 53 01, jet size 51
HDA 159 (346), # 503 97 12 01, jet size 54
HDA 198 (357), # 537 04 47 01, jet size 55
HDA 182 (346), # 503 68 82 01, jet size 56
HDA 199 (357), # 503 94 47 01, jet size 61
 

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surprises with jet size: (I bought them in for some time ago since I was currious )
HDA 154 (350), # 537 07 53 01, jet size 51
HDA 159 (346), # 503 97 12 01, jet size 54
HDA 198 (357), # 537 04 47 01, jet size 55
HDA 182 (346), # 503 68 82 01, jet size 56
HDA 199 (357), # 503 94 47 01, jet size 61

Hi Tor, thanks for this info. It's perplexing to me to see that the HDA-198 and HDA-199 carbs have jet sizes the opposite of what I would expect, and there is quite a difference between the two 357XP carb jet sizes! One has a #55 and the other has a #61 and an accelerator pump, but is listed as an EPA carb! Are you sure about these numbers? I had thought that the accelerator pump was necessary to provide the "oomph" that was lacking due to the smaller jet size which allowed the carb (saw) to meet EPA restrictions.

Interestingly, you say the HDA 182 used on a 50cc saw actually has a larger jet size than the 198 used on a 60cc saw?

Also, the HDA-159 was an EPA carb for the 346XP, its counterpart was an HDA-182. The 159 EPA has smaller jets than the 182. But the HDA-199 was an EPA carb for the 357XP, its counterpart was the HDA-198. However, the 199 EPA has larger jets than the 198?

I wish I had some more info on the throttle bore and the venturi size, but Walbro has changed their website and all the useful information has been scrubbed out. I believe the 198/199 carbs used on the 60cc saws (357xp) had a 16.77mm venturi, while the 159 and 182 carbs used on the 50cc saws (346xp) had a 15.08mm venturi.

The 346 went through a NUMBER of carbs! The 1999 346XP IPL had the HDA-154A and HDA-159A carbs superseded to the HDA-182 and HDA-159 EPA, respectively. Then in 2001 the HDA-182 was superceded to the Zama C3-EL17, while the HDA-159 EPA was superseded to the Zama C3-EL18 EPA. This changed in 2007 when the C3-EL17 was dropped and everything used the C3-EL18, until 2009 when it was superceded to the Zama C3EL32, and then superseded to the Zama C3EL51 in 20011. All the Zama carbs had a 15mm venturi, while the Walbro carbs had a 15.08mm venturi. According the the Walbro website, apparently the 346XP also had an HDA-187 carb at one point? I can't figure out when that was.

Awesome info, thanks for sharing.
 
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Tor R

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Hi Tor, thanks for this info. It's perplexing to me to see that the HDA-198 and HDA-199 carbs have jet sizes the opposite of what I would expect, and there is quite a difference between the two 357XP carb jet sizes! One has a #55 and the other has a #61 and an accelerator pump, but is listed as an EPA carb! Are you sure about these numbers? I had thought that the accelerator pump was necessary to provide the "oomph" that was lacking due to the smaller jet size which allowed the carb (saw) to meet EPA restrictions.
its my understanding that they used the limiters cap to fullfill the EPA restrictions, most of them came adjusted a tad to the lean side.
I'm 100% sure that HDA 199 has a 61 jet, I just double checked with a 199 I have. I belive Scott prefered a HDA 199, and he knows what he is doing.

Interestingly, you say the HDA 182 used on a 50cc saw actually has a larger jet size than the 198 used on a 60cc saw?
and 182 has an accelerator pump as well.

The 346 went through a NUMBER of carbs! The 1999 346XP IPL had the HDA-154A and HDA-159A carbs superseded to the HDA-182 and HDA-159 EPA, respectively. Then in 2001 the HDA-182 was superceded to the Zama C3-EL17, while the HDA-159 EPA was superseded to the Zama C3-EL18 EPA. This changed in 2007 when the C3-EL17 was dropped and everything used the C3-EL18, until 2009 when it was superceded to the Zama C3EL32, and then superseded to the Zama C3EL51 in 20011. All the Zama carbs had a 15mm venturi, while the Walbro carbs had a 15.08mm venturi. According the the Walbro website, apparently the 346XP also had an HDA-187 carb at one point? I can't figure out when that was.
you can set the class of 346 walbro carbs up this way:
HDA 154 A, B, C -> HDA 195, those carbs was mostly used on 340/345/350, and rarerly used on 346, most likely never used on 346.
HDA 159 -> HDA 196, 346 EPA carb.
HDA 182 -> HDA 197, 346 non EPA carb, but it has accelerator pump though.

HDA 187 is not a carb made for 340/345/346/350 serie, it's for their brush cutter 250R/250RX/252RX, its basically a HDA 159/196 carb with a few extras and different shafts.

Another Zama carb you forgot is your list (it was used on Husqvarna 355)
Zama C3-EL16, 15mm venturi EPA.
Zama C3-EL15, 15 mm venturi non EPA.

This changed in 2007 when the C3-EL17 was dropped and everything used the C3-EL18, until 2009 when it was superceded to the Zama C3EL32, and then superseded to the Zama C3EL51 in 20011
Zama C3EL32 was introduced in 2007 month 8 with 346 NE
 
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Tor R

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Walbro has never provided instructions or parts to service the accelerator pump. Whether due to fuel quality or simply a limited lifetime, the accelerator pump would often get gummed up and stick, causing running problems. The easy fix was to replace the whole carb, as most small-engine technicians were not going to go through the trouble to diagnose, remove, service, and replace an accelerator pump.
walbro have had or has accelerator kit to several of their carburetors with the pump. I belive the items has # 160-xxx or 160-xxx-x

. In April 2003 Husqvarna updated their 357XP and 359 to use 4 new carbs! All four carbs still use a 16.66mm venturi. The particular carb choice is dependent on two qualifications: the first is if the saw came with handle heating (357XPG and 359G) or without handle heating (357XP and 359), and the second qualification is if the saw was sold in a locale requiring EPA regulation compliance, or not. Saws with handle heating received a Walbro HDA-190A, or a Walbro HDA-191A if they needed to meet EPA regulations. Saws without handle heating received a Walbro HDA-198A, or a Walbro HDA-199A if they needed to meet EPA regulations.
its not that plain simple with the conclussion of HDA 190/191 vs HDA 198/199.
The amount 357/359's I had in the last years are limited but I've not seen a XPG/G saw where it also had carb heaters.
I probleby had ruffly 20 346XPG/353G through my hands the last 3 years, so far I've had just had one with carb heaters.
Those two heaters cost ruffly 120-150$ in total, its my understanding that Husky only sold saws with carb heaters for those marked/areas where carb icing can happen quite often.
 

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My OE 346xpg has the heaters on the carb.
that make sense for me Brian, in their first years they used the same generator on them all, later, most of my OE generators has the split for carb heaters even those I had never came with the carb heaters mounted.
I don't know why and where they generally sold them G saws with the carb heaters.
I would think they really started to sort it out when they changed the rear heat element and front handle bars, around 2004, my 05-06 models didnt have the wire attachment for carb heaters.
 

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I’ve seen two 346xpg’s (one in person, one on eBay) with the carb heater here in the states, and I bought used (but working) carb heater parts from a local repair shop for my saw to retrofit... so it has it now.

I made the plastic ring on the 191 and 199 carb out of aluminum and opened the impulse line so it works better and can be used with the thermostat and carb heater now. I mounted it on a 198, but I am curious if I should also change the jet to the 199 jet.

I do see a pump kit with part # 160-xxx, but it is unavailable. I would probably just machine a new accelerator pump on the lathe if I ever went to a 199, and the pump was failing, and I didn’t have a backup.
 

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Screen-Shot-2018-11-03-at-7-43-47-PM.png


I just found this post elsewhere on the web, and I wanted to bring it over here for reference purposes.

No gas engine will accelerate off a lean carb. Because of this, the newest generation of lean running carbs give the intake a shot of fuel to provide for the rpm transition.

With a chainsaw or weed whacker with a regular carburetor, the low speed circuit has to be tuned richer so that the engine can accelerate to high speed. Therefore during normal idling, the engine runs rich. The best tuning for the low speed normally is to make the low speed as lean as possible where the engine will still be able to accelerate when you jerk the trigger.

With an accelerator pump carburetor, the idle needle can be tuned leaner for running at idle and the engine will still accelerate to high speed.

I experienced a problem with a new chainsaw and it took me a moment to figure out what was wrong because I didn't know in the beginning that the carburetor was different. I have a Husqvarna 357XP with the HDA-199 carburetor and this is an accelerator pump carburetor. When I first bought the saw, it would quit on me in the lower mid range speed area unless you wiggled the trigger a little every now and then. I then discovered that the carb had an accelerator pump and that for some reason the midrange was lean and the accelerator pump that would keep the chainsaw running was failing. I finally decided to make the low speed a little richer and the midrange running problem went away.

With this knowledge of the operation of my 357XP I feel that I would know if the accelerator pump would not work. But I also see the possibility that a bad accelerator pump carb could be tuned to run the chainsaw with a bad pump by making the mixtures richer but the overall running characteristics would not be as good as original new condition.

I believe that the general problems with the accelerator pump Walbro HDA199 lead Husqvarna to change to a Zama carb on later 357XP models.
 

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I can still get the HDA-198-1 new from one of my suppliers (when the local warehouse isn't out of stock for two months) and they are pretty reasonably priced.
 

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I can still get the HDA-198-1 new from one of my suppliers (when the local warehouse isn't out of stock for two months) and they are pretty reasonably priced.
A long shot, but can you still get them?
 
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