Chainsaw Repair

The 42.5 mm is the biggest you can go with that family. The engine is a clamshell design with the cylinder and the upper half of the crankcase as one piece. Not a whole lot you can do with them. Most of the 025/MS250 is plastic with a metal engine unit sandwiched inside.

The 026/MS260 is a engine with a separate cylinder and crankcase. The crankcase serves as part of the frame of the whole chainsaw.

The MS250 responds well to opening up the muffler (Muffler Mod), Installing a WT215 Walbro carb ($22.45) but with most of them you will also need a tank vent/needle valve guide to match the WT215 with it's needle valves close together. Most MS250's came from the factory with a Zama carb with the High speed needle at the back of the carb and the low speed needle down low at the front of the carburetor.

Most of the aftermarket flocked air filters are very restrictive. You can get a aftermarket nylon mesh filter that lets them breathe better.

In spite of the MS250 normally coming with a 18" bar, .325 / .063 chain, I like the 16" bar with Stihl RS chisel (Yellow) chain.

Set up this way, they are a pretty hot little limbing saw.

Thank you for the reply. What is the needle valve guide?  Why I was wanting to know about the 260 was the 44mm piston it is just a fuze bigger than the 250's. Thought there might be a possibility of a jug swap. And also I have noticed china made jugs, pistons and overhaul kits are very cheap. Are these good quality replacement parts or have people been having problems with them.

The 260 is made different. the 250 does not have a jug as such. There is no way they will fit each other.

China made jugs are hit and miss. You cannot depend on the quality and even if they are the best, they never get better than genuine OEM. Hyway brand seems the most consistent.

The needle valve guide is a rubber piece that fits over the three adjustment screws on the side of the carburetor to the outlet holes on the outside of the chainsaw.

To mod the muffler . . .

Remove the muffler from the engine by removing the two nuts.

Lift the spark screen cover from the muffler.

There is a rectangle depression in the main muffler body underneath the spark screen.

This depression typically has a 12mm hole in it. Open the hole up with a round and rectangle file to be as big as the flat part of the depression.

On the side of the muffler body that fastens to the engine, there is a cage in there with several 5mm holes. Open up all these to a larger size that you can.

Be sure to remove all the metal filings from the muffler by washing and blowing it out with a air hose.

Re-install the muffler with the bolts first, then the shield, gasket, muffler, cover, and nuts.

You must re-tune the carb with the mesh air filter and air filter cover installed.