MS250 diagnosis

[flybyjohn]

Hi everybody. I don't know if I have ever posted much here (didn't even know I was registered until I tried to sign up again) but I get quite a bit of advise from this site by reading previous posts. I am now hoping to find some advise on a saw I have that have not been able to find by searching the web.

I have a MS250 that I don't know the history of. Found it on the side of the road about 4 -5 years ago with a broken handle and some other minor scuffs and bruises. The saw started fine and ran at the time. I replaced the handle and tuned up the carb and the saw ran great. I use it only occasionally because my 034 super is usually my go to saw. I started having problems with it last year and the symptoms are the same now as when it started having problems.

Here's the problem. the saw fires fine after 3-4 pulls at full choke, take choke off and the saw fires up by the 2nd pull. It will idle ok (maybe a little fast) but I needed to richen up the low speed needle (not the idle set) about 1/4 to 1/2 turn more than normal to keep it running. If you go to full throttle right after it starts it will rev and keep running fine but if you don't go to full throttle right away or you let off of full throttle and try to run the saw at half throttle, it will sound like it is bogging and die. If you don't touch the throttle it will continue to idle but as soon as you go to open the throttle it is a struggle of feathering on and off the throttle to get it to increase rpms. Most of the time it will die and only go to full throttle after you choke it again and then take the choke off.

I have checked the fuel line and impulse line and both hold a vacuum, never tried to pressurize them. The fuel tank vent is working. I took apart the carb and cleaned it out good with seafoam and blew all the passages out with light air pressure. I am not sure where to go from here, I have some crank seals on the way. figured for under 10 dollars and a couple hours of work that would eliminate that as a problem. I don't want to get a new carb yet because it seems that if it runs fine at idle and full throttle, there shouldn't be a problem with the carb.

Please let me know if there is something I should be looking at to get this thing running again. The 034 super is a great saw but the 250 is quite a bit lighter for limbing.

 

[DND 9000]

I would pressure test the crankcase and engine with both possitive and negative pressure. There is maybe somewhere an air leak. Also check the carb with pressure that it is tight. If possible give the carb a cleaning with the ultrasonic cleaner and replace all diaphragms and gaskets and inlet needle with lever. Sometimes the carbs on the MS 250 have problems with the accelerator pump, could also be a problem. If the pump piston is worn out, I would go straight for a new carburetor or an aftermarket one without accelerater pump. These were just a few thoughts from me what to check.

 

[HarleyT]

Which seals did you order?

 

[HarleyT]

this tech bulletin addresses the seals.

 

[Ozhoo]

...it seems that if it runs fine at idle and full throttle, there shouldn't be a problem with the carb.

If it has a ZAMA carb, that's a bad assumption.

 

[flybyjohn]

I ordered these seals off of Amazon "HIPA Pack of 2 Cylinder Crankshaft Bearing Oil Seal 15 x 25 x 5 for STIHL MS170 MS180 MS210 MS230 MS250 017 018 021 023 025 Chainsaw"

With this saw it seams like it will be probably less time consuming to pull the bottom clam shell off and just put a couple new seals in instead of trying to pull the old seals out without splitting the case.

It is a Zama carb. I think the numbers on the side were "s76c" . What should I do with the Zama carb to fix it or should I just chuck it and get a new one? I was trying to figure out where an accelerator pump would be in the carb but couldn't find the schematic of the carb. When I think of accelerator pump on a carb, my mind goes back to the quadrajets and Holley carbs that shoot a pint of fuel in the ventures when the throttle is depressed. I don't see anything mechanical on this carb that would do that unless it is vacuum actuated.

 

[Ozhoo]

That's pretty much the same operation as your zama, only the pump is activated off the throttle shaft. Works great until the parts wear and then you start having acceleration problems.

Accelerator pump parts are circled.


You can get a knock-off WT-215 for 10 bucks on eBay.

 

[flybyjohn]

Thanks, I will try a new carb before tearing the saw apart.

 

[HarleyT]

Just get a new carb at the Stihl dealer

 

[HarleyT]

1123 120 0603 CARBURETOR (MS250) 21.99


1123 120 0604 CARBURETOR (MS210) 21.99

1123 120 0605 CARBURETOR 21.99

 

[HarleyT]

#1123 120 0605 is the Walbro wt-215

 

[flybyjohn]

Your dealer is a lot more reasonable than mine. They wanted 30.00 for the crank seals and nearly 50 for the zama carb. That's for parts only. They did want to sell me a new saw though. Told me if it needed any work then it would be better to just buy a new saw because any labor would be over $200.00

 

[flybyjohn]

EBay's Zama carb is 40.00 for oem.

Is the Walbro better than the Zama? it doesn't look like the low and high needles are the same spacing on the two carbs.

 

[HarleyT]

I prefer the Walbro, over Zama anyday. I'll send you our pricelist, for our region.

 

[Ozhoo]

The ZAMA's have accelerator pumps, while the Walbro does NOT. If you're given the choice, go for the Walbro.

 

[flybyjohn]

Dealer price here was 35.00. He said that the price should be the same nation wide and didn't know where they came up with the 21.99 price.

 

[HarleyT]

Been that price in the Ohio region for years.

 

[flybyjohn]

Another question. I ran across a fix for the accelerator pumps in the 200t carbs in an arboristsite thread that just removed the pump cylinder and plugged the hole with jb weld. Some used the cylinder along with jb weld but I don't think it would be necessary if you just filled the hole with jb weld. Of the threads I read on this subject, only one person commented that the saw was too rich on idle when set to be able to transition without a flat spot. He drilled out a small orifice to the next larger size and it fixed the problem. All the others that used this fix said the saws ran perfect after the fix.

I think that since I have a new carb already on the way, I might try to do this with my original carb just to see if this is indeed my problem. If this works on a 200 do you all think it might work on the 250 also?

 

[Ozhoo]

I'm a bad person to respond since I'm an accelerator pump hater... but yes, it'll work. Did you find pictures of what you need to do?

 

[flybyjohn]

Yes. looks like a 20 minute job and then wait overnight for it to cure. I was thinking of just machining a small aluminum plug that I can press fit in and then I don't have to wait. Just press in, put back together and then bolt on and try it.