MS660 carb adjustment questions

[Andy B.]

I have a new MS660 I picked up about a month ago.  So far I only have a tank of fuel through it just cutting down a few trees and cutting some firewood logs.  I know, I should be out working that beast!

This is a brand new saw.  I have been reading a lot about the mixture settings and oil mixes as I get ready to use the saw with a chainsaw mill.  The carb adjustment screws are the "3/4 and 1/2" screws, and not the "1 and 1" screws.  If you know about a MS660, you will know what I mean.  From my reading, I would think that this means I have one of the newer carbs that can't really be adjusted much.  I was thinking of making the saw run slightly richer, but the High adjustment is maxed out at the 3/4 turn setting.

Also, I have been using 91 octane gas and the Stihl synthetic oil mixed at the recommended 50:1 ratio.

As an aside, I am very familiar with 2 cycle engines and back in my younger days built a few 2 cycle racing quad engines as well as a bunch of radio control car engines.  I know a chainsaw isn't a racing quad or radio control car, but I have no fear of playing around with engines.  I never blew up any in the past, well, not accidentally.  :D

My first question is, should I go to 40:1 on the oil mix for a few tankfuls, or should I stay with 50:1?  I just want to do what is best for the engine.  For milling would it be better at 40:1?

Second, since the saw is new and has a two year warranty, should I fudge around with the carb settings?  It really seems that you guys recommend going a little rich when using a CSM.  I think that the only way to richen the settings is to remove some boot or limiter or something that I see mentioned quite frequently when discussing the newer saws.  My Stihl dealer is a pretty cool cat, so I don't think I'd have a problem if a warranty issue popped up, but if there is no reason for me to richen the settings, I won't do it.  Honestly, my 026 Pro is 15 years old, and runs fine, and I have no reason to think I will ever have a warranty issue with this MS660.

Presently the saw runs great, and with only one tank of fuel through it I expect it to only run better.

Andy B.

[celliott]

If you take the carb off, you will see plastic tabs on the H and L screws that limit adjustment. No big deal to trim these off with an exacto knife and there you go, full adjustment. However, I would be pretty certain that would void your warranty....
I wouldn't do anything to void the warranty of a brand new saw. Not that I've ever, or ever will, have a brand new saw   :D The used ones work just fine for me, I'll keep them running.

[Andy B.]

Chris,

Thanks for the reply.  So I will take that as one vote against any mods.  :D

The saw runs great, but like I said, I just want to keep it running great while using it in the mill.  I specifically told the dealer what I will be doing with it, and his only comment was, "That's what a lot of guys buy these for."  I guess if he thought there would be an issue he would have said something.

Andy B.

[celliott]

Milling is hard work for a saw. I'd just make sure to go slow, don't overwork the saw, and let it cool down. And keep the chain very sharp. If you do have an itch to do something to your new saw, stihl does offer a dual port muffler cover for the 660 I believe, or maybe it's only the 460. Thought it's been mentioned in a thread somewhere. Anyways, that could dissipate a bit of heat and up the power a bit too, and it's a stihl part so probably wouldn't hurt the warranty.

Found one on baileys- http://www.baileysonline.com/Chainsaws/Chainsaw-Parts/Muffler-Exhaust/Stihl/Stihl-Muffler-Cover-Dual-Port-for-066-MS-650-MS-660-Chainsaws.axd

I'm looking to get a big saw and a CSM myself. The 066\660 is on my list of saws to look for   :P

[JohnG28]

There is a way around voiding the warranty. You have to be careful not to mess up the limit caps when pulling them out so they don't show obvious damage. As I recall from my 361 the tab that stops the screw from spinning further hits a stop at the extreme out position.  This is was also the position where they can be pulled out. Pull the cap(s) off and then adjust the carb with the limit caps off. Once happy pop them back in, intact, and the saw is adjusted richer and still has intact limit caps. As far as you know nobody ever touched them. ;)

[ladylake]

You might need the warranty if you don't richen it up a little for milling.  Steve

[NCFarmboy]

Carry back to dealer, tell him what you are doing (milling) ask him to richen it up.  Warranty will then be safe.  DP muffler cover is a nust IMB.  Also use more oil in mix I'd suggest 32-1 even w/Ultra.  Milling is hard on one.  If you choose to use more oil it must be tuned with mix you will be using. JMO!
Shep

[Andy B.]

Thanks guys!

Chris,

I did read the dual port muffler threads.  It sounds like if I did that I would definitely need to richen the carb a little.  I am thinking of buying the dual port cover while they are still around but probably won't put it on until the warranty is almost up because I could see that voiding the warranty for sure.

I'm going to have to search YouTube to see if there is a video of these limiters and how to get to them.  Do any of you know offhand if there is a thread here with photos of the process to get at the 660 carb and these limiters?  I don't recall one in my searching.  I'm going to go search again.....

Shep,

I just saw you posted while I was typing my reply.  I will call the dealer and ask if he will adjust it slightly richer.  I didn't think to ask him.

Andy B.

[JohnG28]

If you buy the dual port cover from your dealer they will make any needed adjustments for you.

[joe_indi]

I wouldnt advice fooling with the limiter caps on a new saw.Any 'art work' however careful you are could be e cited as the reason for refusing a warranty  just in case you manage to have any issues.
Safer thing would be to replace the standard 0.64 carb jet with a bigger one.The MS460 uses a 0.68. This will ensure a richer high speed mixture without messing up the limiter caps.
Plus this change is reversible any time. Richer jet will make the saw safer on a mill, but might  make it less fuel efficient.

Joe

[Andy B.]

Thanks again guys.  It turns out it was much-a-do about nothing.  I did some searching and reading, and about 2 minutes with an 8mm socket and a 2.5mm screw from the radio control car spare parts box, and the problem is solved.  No modifications needed and all factory parts are still installed.

In fact, I don't even think an 8mm socket is really needed now that I understand the "top secret classified" procedure.  ;)

Andy B.