Muffler Mod Gone Awry

   / Muffler Mod Gone Awry #1  


Elite Member
Mar 11, 2007
ISEKI TA 247. Stihl Saws Gravely Zt's Polaris ATV's State Of The Art Welding Equipment
I took my 044 mag muffler cover off. It was empty inside. I had bought a dual port muffler cover for a modification. Did the install and according to much research including U-Tube video's. I opened up the H screw another 3/8" and fired it up. Sounded like motocross bike. It was 4 stroking pretty good so I turned the H in a click from like 12 oclock to 1 oclock and idled it down 1/8 turn so the chain would stop. Did a couple test cuts on 20" Cherry logs. It would come out of 4 stroke in the cut just like I read. It was not over reving although my tach is not here yet. I cut a lot so I know it was less than red line rpms. ( I hope ) Anyway after a dozen wild and amazing cuts, It blew up. LOL.. I know its cheap to repair it but if it was very much 4 cycling and cleaned up in the cut, Why in the #&#^#%&$# would it lock up on me. Fresh non ethanol gas and synthetic oil. Oh well. Tear down begins. :(
   / Muffler Mod Gone Awry #2  
Still could have leaned out too much under load even if it was 4 stroking with no load.
   / Muffler Mod Gone Awry #3  
Just cause it could!!!
   / Muffler Mod Gone Awry #4  
I do not understand the term 4 stroking. Please explain. I will leave my MS440 be. Running 20 inch skip full chisel chain and I am happy with it.
   / Muffler Mod Gone Awry #5  
Could have been ready before the mod and this is just an unlucky coincidence
   / Muffler Mod Gone Awry
  • Thread Starter
I do not understand the term 4 stroking. Please explain. I will leave my MS440 be. Running 20 inch skip full chisel chain and I am happy with it.

It's a de-tuned gurgling sound when running higher rpm's with carb a little rich. Check out carb mods on U-Tube they explain it with the saw running.
   / Muffler Mod Gone Awry
  • Thread Starter
Can anyone recommend a good aftermarket jug and piston kit? 10mm wrist pin. Or is OEM the way to go?
   / Muffler Mod Gone Awry #9  
I doubt it was too lean, if it was 4-stroking in free air at wide open throttle. Loading the saw in the cut simply pulls rpms down, which is why 4-stroking stops. Both screws would have to be way out of whack for it to go from 4-stroking to lean when loaded in the cut.

That said, I don't have a good explanation for what happened, unless somehow the piston or cylinder got messed up during the muffler work (seems unlikely, but go read the arborist site to see all the ways people have eff'd up saws with simple mods).

When I let people use my saws, I have to constantly remind them to lay on the saw to keep the motor loaded. So many people get used to cutting with lousy saws or dull chains, that they go into the "hot knife through butter" mode with a powerful functional saw. Making a dozen cuts that way would be bad.
   / Muffler Mod Gone Awry #10  
While not the quality of OEM, I have had good luck with the NWP kits from baileys. For half the price or less of OEM, The value is better than OEM.