MS260 Muffler Mod/Carb Adjustment

[saxman]

HI All, I really enjoy reading the posts but now I have a question. I have a MS260 with a one screw carb. I like the saw (feel and weight) but it seemed to lack power (18"bar with 3/8ths chain). I saw on this forum how to do a simple muffler modification which I did and I am very impressed with the change in performance. I initially backed the low speed screw out 1/4 to 3/8 turn and adjusted the idle. I used it the other day and it seemed to have a unstable idle and after a long cut it would die. I backed the low speed out more and set the idle again, seems OK now but unloaded engine speed seems pretty fast. I have some questions for you guys
1. Do I need to replace the high speed jet? Most on here say no but I don't want to burn the saw up.
2. Can the use of a tach to check the engine speed insure that the mixture is not too lean?
Thanks in advance for everyone's help.

 

[Lakeside53]

You really need the two (Hi/low) screw carb. Without it you can't adjust for beans. Changing fixed jets is easy, but to get the right one is a pain. If you have trouble finding a carb one, I have a few brand new inexpensive 026 carbs that will suit your need (I got these for for exactly the problem you face). Email me though a private message if you want one.

 

[saxman]

Thanks, I might get in touch with you. I am planning on taking it to my Stihl tech and seek his advice on Saturday. I have noticed that the latest MS260's have 2 screw carbs and the new MS361's, which I have the hots for to go along with my trusty 044.

 

[timberwolf]

Even iif you get the right fixed jet, the saw will never be perfect day to day, Temp and atmospheric conditions change if the jet does not you cant expect to have the saw running idealy day in day out. There were some old threads about the fixed and 2 jet 260 carbs, not sure if there still about.

 

[pbtree]

In plain english, that carb is a PITA. I would change it out if it were me...

 

[saxman]

OK, I get the drift. What are my options? new 2 screw carb from Stihl? from ebay? I tend to agree that to get the optimum performance at all times a fully adjustable carb is necessary.

 

[Lakeside53]

Stihl = $90, Me : a LOT cheaper (but I'd take $90

 

[saxman]

UPDATE: I took my saw to the dealer on Friday. The tech put it on the tach and he told me it was turning 14,100 which is fine. He said the carb was adjusted correctly and what I did would cause no problem. I still agee with others that a fully adjustable carb would be better but I will give this a chance. Thanks to all for their input. Anyone got anything to add?

 

[Lakeside53]

Your original complaint was an unstable idle. That has nothing to do with the high jets, and probably nothing to do with the carb at all. Assuming the piston is In good shape, and you've tuend the L screw correctly, most likely cause is an air leak and probably from the crank shaft seals, and about 80% chance it's the one under the flywheel.

You have two choices, neither good if you don't have the tools.

1) pressure test the entire engine. if it passes, then vacuum test. This will show any the seal failure. Replace the faulty seal, test again. You'll need a pressure/vac test set with adapters, flywheel puller and oilseal puller. Yes, it's possible to dig out he oils seals by hand but the flywheel side is very tricky and easy to damage the casing.

2) Just replace both seals, don't test it and hope you get it right (90% chance).



The other choice - just turn up the idle screw and richen the L, and live with it... It will get worse over time though.