If you want to get the most out of your 250, read on.
The stock muffler totally chokes the saw. A good start is to drill more holes in the exit, but this doesn't completely solve the problem. The internal baffle is restrictive and must be dealt with.
One good mod is to double the amount of holes in the baffle and reassemble. I've done this and it works well, but there is a better way and this thread deals with that choice.
The muffler will be gutted and changed to open can style.
First, grind open side and bottom seams but leave the top.
Your pieces. Save the baffle, you will need the bolt tubes.
Fab up a baffle using sheet metal, dimensions are 1.35x1.35x.85. Your brazing and bending skills come into play here.
Swiss cheese the top, bottom and back with 1/8 holes. Around 70 should be enough. Debur them all, and clean all the flux off. Leave no chance of something getting back into the cylinder.
Open up the forward can hole and leave a slight raised lip to help center the baffle and braze on. There should be a slight downward tilt to aid flow to the top of the baffle. Clean all the flux off.
Cut the bolt tubes free from the old baffle and place as shown.
Clamp the halves together and braze up.
Paint up with high heat paint. If you haven't already done so, widen the gill slits on the stock deflector and install.
The first give away that it flows better is that the saw idles considerably faster. Then there is a major change in the top end mixture setting, and free revs have picked up quite a bit. Power and revs in the cut are quite a bit higher now also. The baffle works as it should, it flows well, and the noise level isn't objectionable at all, either at idle or full throttle.
A couple of evenings time well spent if you want the most out of your saw. You could probably get even more gains if you replaced the gill slits with an angled tube.
The stock muffler totally chokes the saw. A good start is to drill more holes in the exit, but this doesn't completely solve the problem. The internal baffle is restrictive and must be dealt with.
One good mod is to double the amount of holes in the baffle and reassemble. I've done this and it works well, but there is a better way and this thread deals with that choice.
The muffler will be gutted and changed to open can style.
First, grind open side and bottom seams but leave the top.
Your pieces. Save the baffle, you will need the bolt tubes.
Fab up a baffle using sheet metal, dimensions are 1.35x1.35x.85. Your brazing and bending skills come into play here.
Swiss cheese the top, bottom and back with 1/8 holes. Around 70 should be enough. Debur them all, and clean all the flux off. Leave no chance of something getting back into the cylinder.
Open up the forward can hole and leave a slight raised lip to help center the baffle and braze on. There should be a slight downward tilt to aid flow to the top of the baffle. Clean all the flux off.
Cut the bolt tubes free from the old baffle and place as shown.
Clamp the halves together and braze up.
Paint up with high heat paint. If you haven't already done so, widen the gill slits on the stock deflector and install.
The first give away that it flows better is that the saw idles considerably faster. Then there is a major change in the top end mixture setting, and free revs have picked up quite a bit. Power and revs in the cut are quite a bit higher now also. The baffle works as it should, it flows well, and the noise level isn't objectionable at all, either at idle or full throttle.
A couple of evenings time well spent if you want the most out of your saw. You could probably get even more gains if you replaced the gill slits with an angled tube.
