Don’t Write Off Your MS250 with a Zama Carb

[Alphadelta]

This is meant to be an informative post and save someone time and money. I picked up a MS250C with a Zama carb couple years ago for pretty cheap on account it didn’t run very well. Got it home, cleaned it up, did the typical basic carb clean and tuned it the best I could. But it never really ran right, it was fickle and every time I picked it up I wondered what weird behavior I was going to have to deal with. But it was the backup saw so never investigated further; decided today that needed to change.

Yanked it apart, took the carb out, checked the jets, they all looked decent. Put it back together and yep still runs awful, if it would run at all. Read some forum posts and decided just for kicks before I resigned and had the local shop take a look I would REALLY clean the carb. I took everything off the carb I could without removing roll pins or wrenching on it. Then it sat the ultrasonic cleaner with just simple green and hot water for 10 minutes, pulled it out, blew low pressure air through it, back into the vat for 5 more minutes to finish it off.

Put it back together, did the service manual factory settings for the carb (all the way seated back one turn on both high and low screws) started it and…. It was still running poorly and for some reason while in high idle I hit the primer bulb just because I wanted to see how it acted, it sputtered then settled right down. It runs like an absolute dream! My jaw hit the floor. I have NO idea what pressing the primer bulb did, maybe the diaphragm was stuck in an odd position but I digress. Why after having this saw for 4 years I didn’t spend the extra 1 hour to really clean it is beyond me. I was about ready to write this thing off so -

My point is before you right off your 250 with a Zama carb and start throwing parts and energy into it - really give that carb some love and do your best to clean it out really, really well. Ultrasonic cleaner is your friend, I’ve heard Seafoam works really well. If you don’t want to buy an ultrasonic (or use your wife’s), they sell small carb cleaning needles on Amazon for cheap. Make sure you’re diligent with your cleaning process, go slow, tear it down as much as you can so any contamination inside the carb doesn’t get stuck and your cleaner has access to it. No high pressure air and start with the factory tune settings. I could have sworn I did a decent cleaning job when I first bought it and always chalked it up to ghost in the machine. Also check the fuel line into the carb plenty of forum posts about it getting pinched and starving the saw when you go to rev it up.

Hope this helps someone out there who was/is equally frustrated with their 250.

Be safe all.

 

[farmguywithasaw]

I threw the Zama c1q away and put on a walbro from an 025. Starts easy and runs smooth

 

[Pjohnson]

My 251 been sitting on the bench the last 4 years bout ready to throw it away

 

[SteveSr]

My 251 been sitting on the bench the last 4 years bout ready to throw it away

MS251 is a TOTALLY DIFFERENT animal. Any comparisons are apples to oranges.

 

[Pjohnson]

MS251 is a TOTALLY DIFFERENT animal. Any comparisons are apples to oranges.

Actually it's been a pretty good saw it's probably 25 years old. It's just been really temperamental the last few years. I should throw a carb on it, but I got a few other saws so hasn't been a high priority

 

[dudz3636]

I threw the Zama c1q away and put on a walbro from an 025. Starts easy and runs smooth

I'll second this. If I recall, the MS250 Zamas have an accelerator circuit/pump that's prone to leakage. Supposedly there is a fix by just plugging the circuit with JB weld. But I did the same exact thing- Walbro from an 025.

 

[Pjohnson]

I'll second this. If I recall, the MS250 Zamas have an accelerator circuit/pump that's prone to leakage. Supposedly there is a fix by just plugging the circuit with JB weld. But I did the same exact thing- Walbro from an 025.

Where do i get one of these carbs

 

[dudz3636]

Where do i get one of these carbs

I don't know if the MS250/025 Walbro carb is interchangeable with the MS251 you mentioned you have. I suspect it is not. As SteveSr mentioned, the problems being talked about in this thread relative to MS250 Zama carbs may very well be completely irrelevant to the MS251. Sorry, I simply don't have any personal experience with an MS251 to offer any constructive advice.

 

[Pjohnson]

I don't know if the MS250/025 Walbro carb is interchangeable with the MS251 you mentioned you have. I suspect it is not. As SteveSr mentioned, the problems being talked about in this thread relative to MS250 Zama carbs may very well be completely irrelevant to the MS251. Sorry, I simply don't have any personal experience with an MS251 to offer any constructive advice.

I'll have to look pretty sure it's a 250 it's at least 25 years old

 

[dudz3636]

I'll have to look pretty sure it's a 250 it's at least 25 years old

I purchased a Walbro WT-215 for around $40 on eBay. It works, but if I recall the H/L adjustment holes in the plastics/handle on an MS250 are slightly different than the 025.

 

[SteveSr]

...but if I recall the H/L adjustment holes in the plastics/handle on an MS250 are slightly different than the 025.

Yes, you will need a new carb screw grommet. They are available from Stihl. There are two types depending on tank vent style.

 

[a. palmer jr.]

I'll second this. If I recall, the MS250 Zamas have an accelerator circuit/pump that's prone to leakage. Supposedly there is a fix by just plugging the circuit with JB weld. But I did the same exact thing- Walbro from an 025.

I hadn't noticed a leak in any of the Zamas I've installed but then again they were new.

 

[dudz3636]

I hadn't noticed a leak in any of the Zamas I've installed but then again they were new.

It's something that develops over time from what I understand. Perhaps it was ignorant of me to do so and there's a simple fix, but I vowed never to rebuild/reinstall that particular model Zama (C1Q S76C I think) in an MS250 again. The few 250's that have come my way from friends I convert to Walbros because it's inexpensive to do so.

There's probably someone out there that knows much more about these carbs than I. This is just my experience, so take it for what it's worth.

 

[dudz3636]

It was bugging me, and I knew I had kept a couple of those carbs as reminders. Both are Zama C1Q S76 carbs. I believe the accelerator pump is on the intake side and is held in place by the choke shaft in the chamber at the top right of each carb. The carb on top is intact for reference. The carb at the bottom of the photo shows the brass accelerator pump removed and the associated oring that can leak.

 

[stihltech]

I usually find water in the fuel prior to the pump failing or old fuel. Also remember to check the off idle ports in the throat of the carburetor. Tag wire probing has fixed a few.

 

[a. palmer jr.]

It's something that develops over time from what I understand. Perhaps it was ignorant of me to do so and there's a simple fix, but I vowed never to rebuild/reinstall that particular model Zama (C1Q S76C I think) in an MS250 again. The few 250's that have come my way from friends I convert to Walbros because it's inexpensive to do so.

There's probably someone out there that knows much more about these carbs than I. This is just my experience, so take it for what it's worth.

I don't even think mine were real Zama carbs but Zama knock offs. I just installed them because they were about the same price as a rebuild kit and less work. I haven't had any complaints yet.

 

[freeasaburt]

I don't know if it's sold on your side of the Atlantic, but for ulrasonic cleaning of carbs (and other stuff too) I add Tickopur R33. Expensive, but works absolutely great and you only have to mix at a ratio of 3 - 5%. Ideally, max temp of your water/R33 mix is 60°C (140° F).

On a sidenote: I recently tested a new MS251 with a 3/8 lo pro chain and have to say I was quite impressed, performed better than I expected. Only saw I used that kind of chain on before was a battery powered one.
Loud too, I kinda expected a new saw sold here in Europe to have a way too restricted exhaust, I didn't check its interior but the saw seems to breathe quite well.

 

[SteveSr]

On a sidenote: I recently tested a new MS251 with a 3/8 lo pro chain and have to say I was quite impressed, performed better than I expected. Only saw I used that kind of chain on before was a battery powered one.

These run good because they are borderline lean. They won't tolerate abuse like a dull chain or old fuel, or really cold (sub-freezing) weather without burning up. The last one that I rebuilt I removed the "H" limiter and opened the needle up another 3/4 turn and reinstalled the limiter.

Loud too, I kinda expected a new saw sold here in Europe to have a way too restricted exhaust, I didn't check its interior but the saw seems to breathe quite well.

The 251 is a strato saw that doesn't need a choked muffler for emissions.

 

[Wood Doctor]

Primer bulbs cause more problems with saw engines than any saw engine without a primer bulb installed. When the bulb hardens up and cracks, you have to replace it. Simple as that.

 

[SteveSr]

Primer bulbs cause more problems with saw engines than any saw engine without a primer bulb installed.

This goes for any 2-stroke with a primer bulb. The usual issues are the 2 extra check valves needed to make the system work.

When the bulb hardens up and cracks, you have to replace it. Simple as that.

As long as the check valves are still working properly the engine will start and run just fine with a busted primer bulb. It will just act like a non-primer engine.