MS 660 Lacks Power

[deursen07]

I bought a used 660 and replaced the scored piston and cylinder with a big bore kit. It runs fine but doesn't have as much power as I thought it would. It cuts as fast as my 036 which doesn't seem right to me. It has 150 psi compression and I cleaned the carb and filter. Max rpm is set at 12,600 right now. Any suggestions would be great. I have no idea whats wrong with it.

 

[blsnelling]

I bought a used 660 and replaced the scored piston and cylinder with a big bore kit. It runs fine but doesn't have as much power as I thought it would. It cuts as fast as my 036 which doesn't seem right to me. It has 150 psi compression and I cleaned the carb and filter. Max rpm is set at 12,600 right now. Any suggestions would be great. I have no idea whats wrong with it.

Sounds like you've got it set too rich. You're not going to be able to go by factory RPM specs. You'll have to tune it by ear and then fine tune with timed cuts.

 

[deursen07]

I was fearful of running too lean since that's what destroyed the piston and cylinder the first time. What should I set the needles at initially?

 

[Wet1]

If it has good compression and runs good, it shouldn't be a dog. As stated above, it probably needs to be tuned.

Here's a good write-up on how to tune the carb. There are also audio clips included which really help explain what they are talking about.
http://www.madsens1.com/saw carb tune.htm

 

[blsnelling]

I was fearful of running too lean since that's what destroyed the piston and cylinder the first time. What should I set the needles at initially?

Initial settings are not going to be critical since you're only going to use that to get it started and tune from there. 1 turn is pretty standard.

 

[Jacob J.]

On the high end you should lean it out to the point where it just stops "four-cycling". You'll easily be able to tell by listening. The last 660 I put a big bore kit on had a sweet spot at 14,100 and that was with no porting, since the port timing on the big bore kits is already different than the Mahle cylinders.

 

[056kid]

On the high end you should lean it out to the point You'll easily be able to tell by listening. The last 660 I put a big bore kit on had a sweet spot at 14,100 and that was with no porting, since the port timing on the big bore kits is already different than the Mahle cylinders.

" where it just stops "four-cycling". " Wont that be just alittle too lean??

I thought that it was best to get to the very top of the 4 cycling

 

[Jacob J.]

Wont that be just alittle too lean??

Nah. If you notice when you're using a tach to tune a modern stock saw like a 460, the top of its four-stroke sounding blubber is usually still 3-400 rpm below the max recommended no-load speed. Variables that affect that include the squish clearance, health of the piston and rings, and health of the fuel system.