Rick Stephens
ArboristSite Operative
Hi ya all. Been reading for quite a while, decided to join and post.
I bought a MS361 kit and a couple extra cylinder kits to try my hand at porting and modding without spending Stihl dollars. All just for the fun of it! I'm on about my fourth iteration of top end builds, and I gotta say I love this saw for a firewood saw. It rocks.
I have a MS440 that was ported by a local shop almost 20 years ago and is my workhorse when logging my place. After all these years with that saw, it still did an admirable job falling, limbing and bucking 25000 MBF of doug and white fir this last spring. I stop at 25 since Idaho state starts charging you commercial taxes and slash inspection fees once you get over 25k. I log my place every couple years and just stop before I get into the tax zone.
Took a 361 big bore piston/cylinder, did some not very radical port work, not changing timing at all. Opened up the muffler with a dual port, added spark arrestor screens to it so I won't burn my world down. Followed my local shop's advice and left compression alone for longevity. This 361 runs pretty darn good. Almost what the heavier 440 does. After doing that, and running it a bunch, it seemed obvious to me the big bore 361 was running out of air. I could get an efficient 13.5k. Then it ran out of fuel and air supply.
So I decided to search out a little more carburetor. Brought in a 440 Farmertech carb, and went to modifying it. Turns out you can swap almost everything over from the smaller 361 Farmertech carb, leaving just the body. Drilled out the intake manifold pulse port on the 440 body so I wouldn't have to reroute the pulse line, swapped over the rods from the 361, had to widen out the flat on the choke rod for the bigger plate, but the throttle plate rod was fine. Swapping over both top and bottom cover plates for diaphragm and pump literally gave me a 361 configuration with a 440 bore. Those plates are exactly identical except for pulse location and air horn style.
Fired her up. No problemo getting er running. And the top end is holy cow mondo bad mutha powerful! Problem is, can't get the idle down from high 3s or even 4k. I know I don't have an air leak. If I stick the tuned 361 carb back on, I am running good.
The 440 carb throttle plate has a notch in it at the top to clear a bump in the bore. I tried to file the bottom edge to get it to close as tightly as possible, but in the end, I probably have to replace the throttle plate since I basically made the sliver of gap only bigger.
I get the feeling that the amount of air flow is more fully closed than my saw will allow to idle at a more reasonable RPM.
I am going to check all the internals of the carburetor next. Runs so good from 4k on up, I don't imagine I'll find anything. And I am sure it is closing as far as it can before running the top of the plate tight against the bore.
Appreciate any thoughts.
Thanks!
Rick
I bought a MS361 kit and a couple extra cylinder kits to try my hand at porting and modding without spending Stihl dollars. All just for the fun of it! I'm on about my fourth iteration of top end builds, and I gotta say I love this saw for a firewood saw. It rocks.
I have a MS440 that was ported by a local shop almost 20 years ago and is my workhorse when logging my place. After all these years with that saw, it still did an admirable job falling, limbing and bucking 25000 MBF of doug and white fir this last spring. I stop at 25 since Idaho state starts charging you commercial taxes and slash inspection fees once you get over 25k. I log my place every couple years and just stop before I get into the tax zone.
Took a 361 big bore piston/cylinder, did some not very radical port work, not changing timing at all. Opened up the muffler with a dual port, added spark arrestor screens to it so I won't burn my world down. Followed my local shop's advice and left compression alone for longevity. This 361 runs pretty darn good. Almost what the heavier 440 does. After doing that, and running it a bunch, it seemed obvious to me the big bore 361 was running out of air. I could get an efficient 13.5k. Then it ran out of fuel and air supply.
So I decided to search out a little more carburetor. Brought in a 440 Farmertech carb, and went to modifying it. Turns out you can swap almost everything over from the smaller 361 Farmertech carb, leaving just the body. Drilled out the intake manifold pulse port on the 440 body so I wouldn't have to reroute the pulse line, swapped over the rods from the 361, had to widen out the flat on the choke rod for the bigger plate, but the throttle plate rod was fine. Swapping over both top and bottom cover plates for diaphragm and pump literally gave me a 361 configuration with a 440 bore. Those plates are exactly identical except for pulse location and air horn style.
Fired her up. No problemo getting er running. And the top end is holy cow mondo bad mutha powerful! Problem is, can't get the idle down from high 3s or even 4k. I know I don't have an air leak. If I stick the tuned 361 carb back on, I am running good.
The 440 carb throttle plate has a notch in it at the top to clear a bump in the bore. I tried to file the bottom edge to get it to close as tightly as possible, but in the end, I probably have to replace the throttle plate since I basically made the sliver of gap only bigger.
I get the feeling that the amount of air flow is more fully closed than my saw will allow to idle at a more reasonable RPM.
I am going to check all the internals of the carburetor next. Runs so good from 4k on up, I don't imagine I'll find anything. And I am sure it is closing as far as it can before running the top of the plate tight against the bore.
Appreciate any thoughts.
Thanks!
Rick
