Don`t leave the chain brake on when you`re blipping the throttle. If you keep doing that, you might as well order a new clutch for it right now. Its still 4-stroking in the cut after your muff/mod. Its still to rich on the high side.

I have done the carb mod that allows you to lean the carb out. It requires a new main jet inside the carb. It is absolutely required if you run these saws at 6-12 thousand feet. FYI those are the easiest saws to work on with most of the screws the same size and torx number. Never use a screw gun to assemble them because you will over tighten and strip screws. Just snug screws on all plastic saws.

Great detailed video showing the whole process all the way through, have done tons of these 590/620’s mods there definitely needed. Stock Muffler has like 8-9 exhaust angle directional flows.

Did the muffler on my cs400. I had the same experience. I kept ramming larger and larger drill bits in there until it all came out and it took awhile. I'm thinking of making a ironhorse style or ram horn for my 620. good job on your saw.

Don’t tweet the throttle with the brake on!

well yur learning. Keeping a saw at optimum operating speed does wonders for cut time, pushing too hard and letting the bar bury beyond the saws power band is a no go. Maybe the muffler mod was a plus, lots of people say it works for all saws but did it now make the muffler non spark arrestor equipped? I would caution to be sure and thoroughly blow out, clean the muffler after that "surgery" as any hard particles can be drawn back in with the engine pulses. My personal view is that some opening up may help but it seems to me people get carried away with that process and go farther than there is a payback for performance. I have looked at a lot of saw mufflers on saws I collect and it looks to me like the supposed restrictions are pretty small in magnitude, the single biggest is the outlet opening shape and diameter. I would be for leaving the internals alone and work on increasing the opening size and air flow capability. Judging from the sound of the engine and the cutting action of the chain you could gain a heck of alot of performance by better carburetor tune and getting that chain to optimum cutting form, more payback there than anywhere else in fussing with saw performance.

If you like playing with your 620 check out gearhead tuning they make some cool stuff for the 620 and West Coast saw make some 3 point dog that are pretty awesome.

Nice work done on opening the muffler. It now moves more air and with it more fuel. I think it's too rich on the High jet now, because we can hear 4-stroking when in the cut.

Very well done detailed video man! Love the saw. Waiting for mine to arrive as we speak. Im wondering if theres a way to not go quite that far hogging it out to keep the noise not quite as obnoxious?. If you had to do it all over again, would you go to that extent on the muffler.

I hope you adjust the high speed on the carb, or it will be running to lean.

***** PLEASE NOTE ***** You will need to use Foam Filter Oil and oil the filter prior to placing it back on the Chain Saw. This was not done in this video and will be done for future installs and cutting!

Don’t hit the dirt bud. You will dull the piss out that chain! Just a friendly reminder or advice however you take it! I’m OCD about chains in dirt lol cause I hand file all the ones at work! Lmao 🤣 great video tho! I got a CS -590 but I run a stihl ms660 & ms362c but I’m building the echo for blocking.

Was much louder after the mod?

Does that muffler work effect the spark arrestor part?

It's a nice video but if you watch the way you cut at the end of the video I can tell that the chain is dull, you should not need to push on the saw like that.

What size bar?

Adjust the high/low now that u did the mod. Lean it out of wood. If not, there's no need to do the mods.

Don’t rev the engine with the brake on!

Follow this video. This will describe how to mod the high circuit of the carb. kzfaq.info/get/bejne/b5mHYMKnt8W8n30.html

Dooood let your saw get up to speed before ya just bury it in the log……