Garage sale rescue: MS260 bogging down

[gtmwoodworking]

So...I rescued a MS260 at a garage sale ($25 with bar and 2 chains!!!). It had a scored piston and cylinder from some unknown issue (straight gas?). It passed passed pressure and vacuum tests prior to tearing it down and again after the rebuild. The saw fired right up and idled fine. When I squeezed the throttle to test it at WOT it died. I've tried just about everything in the book to get it to run correctly:

- New spark plug
- New air filter
- New fuel filter
- Checked spark arresting screen: it was clean
- Checked fuel tank vent: passed
- Adjusted carb screws back to basic settings per bench manual
- Tinkered with High speed screw to observe performance variations: no change
- Pressure tested carb inlet needle: passed

After today's attempts to get it sorted out, I noticed that the outside of the muffler was damp like some fuel was escaping with the exhaust which I've never seen with my other saws. That along with noticing some smoke in the exhaust while testing causes me think that maybe there is an issue with the high speed jet. Possibly dumping way too much fuel into the engine.

I would appreciate your thoughts on the issue. What am I missing? What's the next thing to try? Carb rebuild kit? Replace the carb (Chinese or OEM)? Thank you.

 

[Mafun464]

Id say carb rebuild kit

 

[Hipastore]

It sounds like you have already done a lot of troubleshooting to try and fix the issue with your MS260 chainsaw. The fact that the outside of the muffler is damp and there is smoke in the exhaust could be a sign of a rich fuel mixture, which could be caused by a problem with the carburetor.

Here are some additional things you could try:

1. Check the fuel lines and make sure they are not cracked or leaking. This could cause fuel to be sucked into the engine in greater quantities than necessary, resulting in a rich fuel mixture.
2. Check the fuel pump diaphragm to make sure it is not leaking. If it is, this could cause excess fuel to be pumped into the engine.
3. Check the condition of the carburetor gaskets and make sure they are not damaged or leaking air. Air leaks can cause the engine to run too lean, which can cause it to stall when the throttle is opened.
4. Try cleaning the carburetor thoroughly, especially the high speed jet, with carburetor cleaner.

If none of these steps work, then you may need to consider a carburetor rebuild kit or replacement. You could try a Hipa carburetor ALL-IN-ONE kit with a 10% off code--welcomeback.

 

[berrnard]

So...I rescued a MS260 at a garage sale ($25 with bar and 2 chains!!!). It had a scored piston and cylinder from some unknown issue (straight gas?). It passed passed pressure and vacuum tests prior to tearing it down and again after the rebuild. The saw fired right up and idled fine. When I squeezed the throttle to test it at WOT it died. I've tried just about everything in the book to get it to run correctly:

- New spark plug
- New air filter
- New fuel filter
- Checked spark arresting screen: it was clean
- Checked fuel tank vent: passed
- Adjusted carb screws back to basic settings per bench manual
- Tinkered with High speed screw to observe performance variations: no change
- Pressure tested carb inlet needle: passed

After today's attempts to get it sorted out, I noticed that the outside of the muffler was damp like some fuel was escaping with the exhaust which I've never seen with my other saws. That along with noticing some smoke in the exhaust while testing causes me think that maybe there is an issue with the high speed jet. Possibly dumping way too much fuel into the engine.

I would appreciate your thoughts on the issue. What am I missing? What's the next thing to try? Carb rebuild kit? Replace the carb (Chinese or OEM)? Thank you.

did you adjust the carb at all?

first thing i would do is reset carb to factory

 

[Maine choppa]

I'd say definitely a carb rebuild is in order. Sounds like either it's not getting enough fuel at full throttle or no fuel at all

 

[Mad Professor]

Fatten up LO setting. (CCW, richer)

 

[ballisticdoughnut]

Always rebuild the carb on a new to you saw. Even if it seems to run good, it’s worth doing just for peace of mind. Stay away from the Chinese carbs more often that not they don’t perform like OEM.

 

[Henry E]

Check the air filter. Some have built in chokes and they may not seal or may not stay open correctly. The choke flapper may be closing when there is enough air flow to overcome the spring tension.....

 

[Bubster]

Fuel metering valve

 

[stihltech]

Get a new carburetor. There is a reason the piston was scored. It was not an pressure or vacuum leak. That equals carburetor. Do not rebuild.

 

[a. palmer jr.]

Always rebuild the carb on a new to you saw. Even if it seems to run good, it’s worth doing just for peace of mind. Stay away from the Chinese carbs more often that not they don’t perform like OEM.

Actually, some Chinese carbs are OEM..

 

[ballisticdoughnut]

Actually, some Chinese carbs are OEM..

That’s true.

 

[dmb2613]

time for a WT 194

 

[Vintage Engine Repairs]

Clean the carb, confirm every drilling is clear and put a new oem kit on it. This should help too

 

[Patrick1903]

So...I rescued a MS260 at a garage sale ($25 with bar and 2 chains!!!). It had a scored piston and cylinder from some unknown issue (straight gas?).

Great score. Did you happen upon the deal or do you go out and seek saws at garage sales. I occasionally drop by garage sales when i happen to see them, but don’t seek them out. I’m still waiting to find the ms440 for $25. Pics please!

 

[gtmwoodworking]

Actually, some Chinese carbs are OEM..

Ok. So just for fun I bought one of those $12 Chinese carbs on eBay. Put it in and, just like that, problem solved. So turns out it was the carb all along. Still debating whether to rebuild the OEM one or not. Thanks for all the responses.

 

[gtmwoodworking]

Great score. Did you happen upon the deal or do you go out and seek saws at garage sales. I occasionally drop by garage sales when i happen to see them, but don’t seek them out. I’m still waiting to find the ms440 for $25. Pics please!

 

[Patrick1903]

Ok. So just for fun I bought one of those $12 Chinese carbs on eBay. Put it in and, just like that, problem solved. So turns out it was the carb all along. Still debating whether to rebuild the OEM one or not. Thanks for all the responses.

May as well kit the oem carb for $10 or whatever the diaphragm and gasket kit are. Could be interesting to see if there’s anything apparently wrong with original carb.

Great score. Nice saw.

 

[rupedoggy]

I think the original thing wrong was carb limiters and a man that does not know about them. Notice that the replacement does not have them.

 

[grizz55chev]

So...I rescued a MS260 at a garage sale ($25 with bar and 2 chains!!!). It had a scored piston and cylinder from some unknown issue (straight gas?). It passed passed pressure and vacuum tests prior to tearing it down and again after the rebuild. The saw fired right up and idled fine. When I squeezed the throttle to test it at WOT it died. I've tried just about everything in the book to get it to run correctly:

- New spark plug
- New air filter
- New fuel filter
- Checked spark arresting screen: it was clean
- Checked fuel tank vent: passed
- Adjusted carb screws back to basic settings per bench manual
- Tinkered with High speed screw to observe performance variations: no change
- Pressure tested carb inlet needle: passed

After today's attempts to get it sorted out, I noticed that the outside of the muffler was damp like some fuel was escaping with the exhaust which I've never seen with my other saws. That along with noticing some smoke in the exhaust while testing causes me think that maybe there is an issue with the high speed jet. Possibly dumping way too much fuel into the engine.

I would appreciate your thoughts on the issue. What am I missing? What's the next thing to try? Carb rebuild kit? Replace the carb (Chinese or OEM)? Thank you.

If it was not done already, I would replace the fuel line from the tank to the carb, I would do that as extra ins. Use OEM Stihl fuel line only.