Echo CS590: 14,000 RPM Not What I was Looking For

[Paul Bunions]

I decided to try and tune my CS590 with a 620 carb, no limiters, a Gearhead deflector, and the Gearhead flywheel key that bumps the timing 6 degrees. The saw runs easily, but the top RPM is way too high. Either that or I'm making some kind of tachometer mistake.

Today I put in a new deflector and a key to bump the timing 6 degrees. I set the idle so the chain was still. I tried to find the point on the L screw where the speed started to drop.

I put a cheap tach on the saw and set it so it read 1 RPM every time the plug fired. I got something like 14K RPM, which is just a wee bit high considering that Echo says 12-13K.

I turned the H screw all the way in, and the saw didn't slow down.

Any ideas what I'm doing wrong? I had a 20" bar on it, and the chain was adjusted so about 3 whole pullers or whatever they're called were exposed when I yanked on it. I tested the saw warm.

Here is a summary of the tips I used, copied from Steve's Small Engine Saloon:

1. Have your bar and chain on, as well as the air filter.
2. Start it and warm it up.
3. Turn idle screw CW until chain moves.
4. Turn L back and forth. Speed will drop at extremes. In the middle, there is a top speed. Find it.
5. Loosen L just until you hear the speed start to drop.
6. Adjust idle until the chain is still.
7. Go to H screw and use a tach to set the max RPM.

 

[fleethirte]

just my thoughts.

you did things to modify the saw….
echo recommends 12-13 for the stock saw.
you increased timing…plus a bigger carb which equals more air and fuel.
what happens if a engine gets more air and fuel?
spins faster!!

 

[Paul Bunions]

I can put the old carb on it if I can find it, but I see people on the web claiming the mods and the 620 carb will work together. I also see people saying the ignition limits the speed, but I'm up there near 14K.

I just don't want it to cook itself or blow up while I'm trying to tune it.

 

[Paul Bunions]

Maybe I should spend more than $7 on tachometers?

Well, I think I turned the H screw the wrong way.

 

[Paul Bunions]

Okay, turning the screw the correct way is apparently important. I'm at about 12,500 now. The saw's trigger response is not quite as nice. Tiny hesitation at first. But at least I'm not 1,000 above Echo's recommendations any more.

 

[fleethirte]

what oil ratio you running?
i don’t think if you hold it that high for a short amount of time it will hurt.
when your cutting wood and have a load you won’t reach that’s high of RPM.

what does it sound like to your ears?
is it screaming like a demon or is seem to be about right? then perhaps tach off.

but easiest thing to do is turn h screw out.

turn it out till it starts 4 cycling then go a little back in.

 

[fleethirte]

i think tinman did a similar swap and was comparing RPMs. Might be worth a youtube search..

 

[Paul Bunions]

Thanks for the help. I saw he got 13,300 and was happy about it, and he seems to know a few things. Maybe I'll shoot for that speed and see if I can get the throttle response back.

It didn't sound like it was coming apart. It just sounded too nice.

 

[fleethirte]

there is a sweet spot between screaming demon and to slow lol.

i learned the hard way. had it to high and noticed saw wouldn’t start after i ran her for a bit. also noticed muffler was exhibiting some white looking stuff

 

[ballisticdoughnut]

Sounds like you got it figured out. Further out you turn the high speed mixture screw, lower the rpm will be due to richer AF ratio. Opposite way leaner AF ratio and higher rpm.

 

[Paul Bunions]

I left it at about 13.2-13.3. Now I have to figure out how much oil I want it to sling.

The oil is Red Armor, and I use a heavy 50:1, meaning it may be slightly closer to 40:1. I shoot for 50, but I make sure it's AT LEAST 50, so it may be slightly over.

 

[ballisticdoughnut]

Mix oil ratio is a highly debated topic. Having said that, I run 40:1 in all my two stroke machines and have never had a problem. Little more oil goes a long way in my opinion.

 

[cuttinstihl]

I've got mine tuned to a flat 13,000 with the stock carb and coil. Tried it anywhere from 12k-13.2 and 13,000 flat is sweet spot IME

 

[Paul Bunions]

The throttle response seems better now. I'll see how it cuts, and maybe I'll even find the gumption to take the plug out and check it.

 

[Sidecarflip]

All I changed on my 590 was, I removed the top muffler baffle (which entails carefully grinding off the spot welds, reinstalled the director cover. Changed the ignition module for a 620 module and installed a Nick Stoekel oiled foam air cleaner and velocity stack and ear tuned it to just 4 stroke at WOT. Never even took the OEM limiter caps off the carb. Mine will pull a full cut with a 20" bar no issue and sounds a lot better to boot. I run canned gas in mine, Echo Red Armor 50-1. No complaints on cutting and no complaints on performance either. The stock air cleaner tends to pass fines, it don't seal all that well. Always starts 2nd pull hot or cold and idles nicely. Nice thing about my 590 is, it didn't come with the dreaded CAT in the muffler so that was a non issue. Not sure if the newer ones have a CAT installed however. My CS Top Handle did and it was a chore to remove.

 

[Sidecarflip]

Mix oil ratio is a highly debated topic. Having said that, I run 40:1 in all my two stroke machines and have never had a problem. Little more oil goes a long way in my opinion.

More cannot ever hurt but too little can and will cause issues.

 

[ballisticdoughnut]

More cannot ever hurt but too little can and will cause issues.

Absolutely. Quality of oil makes a difference as well, gonna leave it at that. Don’t think we need another mix oil convo lol.

 

[Paul Bunions]

I don't even know how to tell if my saw has a catalytic converter. It was new in '17.

 

[ballisticdoughnut]

I don't even know how to tell if my saw has a catalytic converter. It was new in '17.

CS590, 600, or 620 never had cat muffler in the US that I know of.

 

[Sidecarflip]

Absolutely not. I really got sick of that thread actually. Ya run what ya run and if it's not right only you get to deal with it.