Stihl 025 Port Timing

[shorthunter]

I have a friend who has asked me to port a new cylinder for his MS250. While I hate working on these saws, I told him that I would port it if thats what he really wanted; he will put it back together.

Here's where you guys come in, I dont know that I can do much to help performance without switching carbs and completely gutting the muffler. Look at the numbers and tell me what you think if you care to comment

Current timing numbers are
Exhaust 96.5/167°
Intake 84.5/169°
Transfers 116°
BD 19.5°

 

[shorthunter]

I know that I can widen the exhaust which will help a little but I don't think he is going to want me to fill the intake. In fact he probably won't want to swap carbs or gut/ weld the muffler

 

[shorthunter]

I feel like the blowdown is pretty close to where it needs to be

 

[huskihl]

Widen the exhaust and intake a little and open the muffler. Maybe some timing advance too

 

[Finnrpm]

 

[drf256]

Tough saw to do much to by design. That clamshell setup makes it tough.

I’m suprised it has so much intake and exhaust duration. The BD seems perfect for a quad.

Like Kev said, widen ex, maybe the intake. Check the size of the Venturi in the carb before you wallow out the intake. If the intake port opening is at least 10% larger than carb bore (not Venturi) I wouldn’t touch it. You’ll likely make it worse.

Unless he will let you open the muffler, which is desperately necessary on that saw, going in the cylinder is a waste of time.

Advance the timing. Add the WT215 carb. If you have a buddy with a Tig and lathe, see if you he can weld a popup onto the piston.

You can go through all of the above, or tell buddy to see it, add the money he might spend on the above, and buy an 026.

I was on the 025 bandwagon not to long ago. Good little saws, but not great little saws.

Here’s one I did a welded popup on.

 

[shorthunter]

Tough saw to do much to by design. That clamshell setup makes it tough.

I’m suprised it has so much intake and exhaust duration. The BD seems perfect for a quad.

Like Kev said, widen ex, maybe the intake. Check the size of the Venturi in the carb before you wallow out the intake. If the intake port opening is at least 10% larger than carb bore (not Venturi) I wouldn’t touch it. You’ll likely make it worse.

Unless he will let you open the muffler, which is desperately necessary on that saw, going in the cylinder is a waste of time.

Advance the timing. Add the WT215 carb. If you have a buddy with a Tig and lathe, see if you he can weld a popup onto the piston.

You can go through all of the above, or tell buddy to see it, add the money he might spend on the above, and buy an 026.

I was on the 025 bandwagon not to long ago. Good little saws, but not great little saws.

Here’s one I did a welded popup on.

View attachment 165926 View attachment 165927 View attachment 165928 View attachment 165929

This is actually a dual port, my aftermarket cylinder is a quad.

Good advice on the intake

 

[drf256]

This is actually a dual port, my aftermarket cylinder is a quad.

Good advice on the intake

Then its an early 025 42mm head.

The later 42.5mm 250 head is a quad oem.

 

[shorthunter]

Here is where we ended

 

[shorthunter]

Pretty rudimentary port work, nothing fancy. Hopefully with the timing advance, muffler mod and carb work it will run well

 

[Deets066]

It’s amazing how much they wake up with a hefty muffler mod. It should run well

 

[smokey7]

Pretty long intake stock on these clams. I still keep thinking about that 270 or 271 Jim did and showed it cutting with a 261. That 270/271 was a bad boy for a clam. So I'm interested in what happens with this saw. Portwork looks great.