Replacing Zama carb that has connection to purge bulb (C1Q-S84B) by a Walbro (WT-215) for MS250

[MMFoF]

I’m having big problems with my MS250 unable to idle (but I can start on high idle setting and it still cuts fine at full throttle), so I’d like to try a new carb.
It seems very difficult to get my hands on a straight OEM replacement in Australia (if anybody in Aus has tips for a homeowner like me on getting Stihl parts, please fire away), plus I’ve seen in other threads that people say the Walbro is a better option.

So if I was to replace the Zama on my MS250 which has the purge bulb and decompression valve with the wt-215, my question is - can I do this? And if so, how do I make it work and do I need to buy any other parts?

 

[Bludenz]

I’m having big problems with my MS250 unable to idle (but I can start on high idle setting and it still cuts fine at full throttle), so I’d like to try a new carb.
It seems very difficult to get my hands on a straight OEM replacement in Australia (if anybody in Aus has tips for a homeowner like me on getting Stihl parts, please fire away), plus I’ve seen in other threads that people say the Walbro is a better option.

So if I was to replace the Zama on my MS250 which has the purge bulb and decompression valve with the wt-215, my question is - can I do this? And if so, how do I make it work and do I need to buy any other parts?

Hey,
Before you even go to Stihl, have you tried resetting the carb to factory settings? Ask @ray benson for a manual and an IPL, and follow the instructions in that. If you've tried that to no avail, have you tried contacting your local Stihl dealer? Easy as a google search "Stihl dealer in *location*". You should be able to send them an email, ask for a quote and provide your carb part number or what your carb is and ask for a new one. It may be a bit pricey, but you'll have a genuine OEM one.

However, before you jump the gun and buy a brand new carb, have you taken apart your carb and cleaned it? That should be the first step, go to your local Stihl dealer, by a carb repair set (carb gasket set) and replace all the gaskets, clean out the jets, etc... YouTube has a few good tutorials on this ("Stihl carburetor clean"). If you've cleaned it and it still doesn't work, then consider replacing your carb.

If it is too expensive (I was quoted $250aud for a ms192t carb), consider trying ebay. Make sure you use ebay.com.au if you are in aus, and set you shipping post code. Search "Stihl ms250 carburetor" and filter by used. This will have a higher chance of showing an OEM one instead of some Chinese knock off. Find one that suits your price range, and check it is the same. Postage may be a little on the pricey side from the US, but would be significant cheaper than one from Stihl.

I've never worked on an MS250, but I've worked on several other ones. This is just my 2 cents and in no way am I an authorised Stihl tech. Good luck fixing the saw!

 

[ray benson]

I’m having big problems with my MS250 unable to idle (but I can start on high idle setting and it still cuts fine at full throttle), so I’d like to try a new carb.
It seems very difficult to get my hands on a straight OEM replacement in Australia (if anybody in Aus has tips for a homeowner like me on getting Stihl parts, please fire away), plus I’ve seen in other threads that people say the Walbro is a better option.

So if I was to replace the Zama on my MS250 which has the purge bulb and decompression valve with the wt-215, my question is - can I do this? And if so, how do I make it work and do I need to buy any other parts?

Check your inbox for a 250 ipl and service manual.

 

[MMFoF]

thankyou!

 

[MMFoF]

Hey,
Before you even go to Stihl, have you tried resetting the carb to factory settings? Ask @ray benson for a manual and an IPL, and follow the instructions in that. If you've tried that to no avail, have you tried contacting your local Stihl dealer? Easy as a google search "Stihl dealer in *location*". You should be able to send them an email, ask for a quote and provide your carb part number or what your carb is and ask for a new one. It may be a bit pricey, but you'll have a genuine OEM one.

However, before you jump the gun and buy a brand new carb, have you taken apart your carb and cleaned it? That should be the first step, go to your local Stihl dealer, by a carb repair set (carb gasket set) and replace all the gaskets, clean out the jets, etc... YouTube has a few good tutorials on this ("Stihl carburetor clean"). If you've cleaned it and it still doesn't work, then consider replacing your carb.

If it is too expensive (I was quoted $250aud for a ms192t carb), consider trying ebay. Make sure you use ebay.com.au if you are in aus, and set you shipping post code. Search "Stihl ms250 carburetor" and filter by used. This will have a higher chance of showing an OEM one instead of some Chinese knock off. Find one that suits your price range, and check it is the same. Postage may be a little on the pricey side from the US, but would be significant cheaper than one from Stihl.

I've never worked on an MS250, but I've worked on several other ones. This is just my 2 cents and in no way am I an authorised Stihl tech. Good luck fixing the saw!

Thanks, I'll take your advice for tracking down parts. As for have I taken apart the carb? Yes I did, but being a newbie at this, I didn't really know how to diagnose a problem. I just sprayed carb spray everywhere. I have not replaced gaskets etc (they did look OK according to some other youtube videos I had looked at). I find it hard to understand if there is a problem with gaskets how it could work so well under full throttle. I did find this thread below that seems to describe very similar symptoms (although I never went to 8 turns on the Low screw!) and it seems the final resolution was to replace the carb.
I'll also look on ebay for used OEMs - hadn't thought of that as an option

https://www.arboristsite.com/threads/stihl-messing-with-my-saw-ms250.335840/

 

[Bludenz]

Thanks, I'll take your advice for tracking down parts. As for have I taken apart the carb? Yes I did, but being a newbie at this, I didn't really know how to diagnose a problem. I just sprayed carb spray everywhere. I have not replaced gaskets etc (they did look OK according to some other youtube videos I had looked at). I find it hard to understand if there is a problem with gaskets how it could work so well under full throttle. I did find this thread below that seems to describe very similar symptoms (although I never went to 8 turns on the Low screw!) and it seems the final resolution was to replace the carb.
I'll also look on ebay for used OEMs - hadn't thought of that as an option

https://www.arboristsite.com/threads/stihl-messing-with-my-saw-ms250.335840/

Gaskets should be fine unless they are stiff to my understanding. As I stated, before you go running off to buy parts, find the part in the Manual that Ray Benson sent you that outlines how to reset the carb to factory settings. Reset to those settings and follow the start up guide and see if it will idle then.

Don't look for the exact part number on ebay, search generic terms, "Stihl ms250 parts lot" or "Stihl ms250 carburetor". If someone parts out a saw and they put up a bulk lot of parts, good chance it will have a carby in it. Chances are that the seller will be happy to separate it as well, in my experience.

Good luck trying to fix it once again

 

[stihltech]

You might want to try this part number-1123 121 5401 valve jet, If it sticks it wont idle. But also be looking for an air leak on the saw. Fuel and pulse hoses are quite common.

 

[MMFoF]

You might want to try this part number-1123 121 5401 valve jet, If it sticks it wont idle. But also be looking for an air leak on the saw. Fuel and pulse hoses are quite common.

Thanks for that advice, I'll look at those hoses too. Can you explain briefly why the valve jet sticking would have an effect on idle but no effect on full throttle behaviour?

 

[MMFoF]

You might want to try this part number-1123 121 5401 valve jet, If it sticks it wont idle. But also be looking for an air leak on the saw. Fuel and pulse hoses are quite common.

@stihltech - just drawing your attention to my question about your response. Thanks

 

[SteveSr]

Thanks for that advice, I'll look at those hoses too. Can you explain briefly why the valve jet sticking would have an effect on idle but no effect on full throttle behaviour?

A dodgy main nozzle jet that doesn't close all the way will create an air leak in the carb which will upset the idle. Zama carbs are known for this, usually producing intermittent symptoms. Unless you are very handy with small mechanical things it is usually easier/better just to replace the carb with a new OEM unit.

 

[MMFoF]

A dodgy main nozzle jet that doesn't close all the way will create an air leak in the carb which will upset the idle. Zama carbs are known for this, usually producing intermittent symptoms. Unless you are very handy with small mechanical things it is usually easier/better just to replace the carb with a new OEM unit.

Thanks @SteveSr - that makes sense. No, I'm not at all handy repairing very small things, although I am still wanting to do my own maintenance if possible. But even the thought of checking on the impulse line as per Stihtech's advice is a bit intimidating because of how much disassembly would be required just to get to it.
Given I don't know for sure that it's the carburetor, and also that the OEMs are hard to get in Australia and very expensive for this version with the connection to a purge bulb, I am considering buying a super cheap replacement carburetor and bypass the purge bulb, purely as a means of diagnosing the issue. i.e. if it is able to idle again, then it's the carb and then I can commit to the price of an OEM (and keep using the cheap one anyway if it seems to work). If no change, then I need to look at the impulse line and fuel line.
What do you think of this strategy for a "non-mechanic" like me?

 

[SteveSr]

Thanks @SteveSrBut even the thought of checking on the impulse line as per Stihtech's advice is a bit intimidating because of how much disassembly would be required just to get to it.
Given I don't know for sure that it's the carburetor, and also that the OEMs are hard to get in Australia and very expensive for this version with the connection to a purge bulb, I am considering buying a super cheap replacement carburetor and bypass the purge bulb, purely as a means of diagnosing the issue. i.e. if it is able to idle again, then it's the carb and then I can commit to the price of an OEM (and keep using the cheap one anyway if it seems to work). If no change, then I need to look at the impulse line and fuel line.
What do you think of this strategy for a "non-mechanic" like me?

It's your money and your time. Cheap Ebay and Amazon carbs are hit and miss at best so you may be replacing a defective part with another defective part. Try to troubleshoot that!

You can also use a non-purge bulb carb to test or use permanently. Just plug the extra hose with a suitable machine screw.

I see that the -S84 has an accelerator pump. These can be problematic, especially in high hour saws. Just ask @lone wolf

The Walbro Wt-215 is an almost drop in replacement. You will obviously loose the purge bulb functionality and you'll also have to change the carb screw grommet to match the carb (see the IPL).

No idle but runs high speed is usually caused by an air leak. It could be the main nozzle or acc pump in the carb or it could be somewhere else.