Another MS390 being stupid....

[isacguy]

There is a difference between dull chain not cutting and no power to cut. Even if you have a dull as snot chain a ms390 has the power to spin the chain relentlessly in the wood throwing saw dust and cutting super slow. Now if you put the chain to wood and you loose power to spin the chain you have problems producing the torque needed to spin the chain to cut.

Also your pop-off pressure could be really weak making the saw flood instead of run hard. Is your cylinder exhaust wet-ish when you're done testing? that would be an indication that too much fuel is being dumped in and causing a super rich condition making the saw bog down and loose power.

Thank you for the chain sharpening advice, I do appreciate it, I will try to improve my skills. I go to Des Moines for work a few times a year, and sometimes Ottumwa, IA, if I can sneak over and say hi one day I will! I will look at the cylinder exhaust if the new chain doesn't fix things tonight, I recall looking at the spark plug after the cutting test, and it didn't seem too overly wet, if that is any indication. I can easily do a pop off test since the carb is sitting on my bench. I'll look up the specs tonight on what they should be.......unless you could just tell me how many pounds it takes lol. I'm still learning all the things I can do with my pressure/vac tester.

It does seem to have no power, from what you were just describing. I have a Jonsered 2159 that the oiler is acting up on, and it flat out DESTROYED the edge on the chain when the oiler stopped oiling when I was using it. It rounded the edges so fast getting hot cutting hedge that it made my head spin. I could certainly push the saw into the cut and throw dust everywhere, I know what you mean. This saw doesn't act like that. Just the weight of the saw pushing down is too much for it.

 

[isacguy]

Here is the new chain vs. the old chain.

The new one does make that old one look pretty rough.....

 

[isacguy]

Ok, I had my beautiful wife take a video, in the dark, with a flashlight, just after a scout meeting. I wasn't really dressed for cutting wood. I just wrapped up firewood last weekend, so the only log I had was this old piece of hackberry. It was certainly less than an ideal situation. I have the new chain on, I applied pressure and vacuum to the fuel line before I reassembled the unit. I also checked the tank vent out with my leak down tester to make sure that it is allowing fuel to flow. It seems to be cutting twice as good honestly, I am going to try and get a proper log to cut that will be a much better test.....more than just 20 sec of work anyway. I'm also going to tweak the carb settings a little after I get it good and warm, it might be almost where we want it to be now. It bogged down a few times, I never took my finger off of the trigger, it was always on full blast, unless I took it out of the cut. When the engine acceleration went up and down, that was because I was varying the pressure I was putting on the saw into the log, from none to about the weight of the saw, trying to get it to run normally. The last time I made a cut in the video shows how it normally bogged down all the time. The cut right before that the saw actually took off pretty good and I think it would have gone all the way through the log. The jury is still out in my opinion if this was my entire problem, but a new chain has certainly made a difference.

 

[HarleyT]

What is the gauge of the new chain? What are all of the numbers off of the bar?

 

[isacguy]

What is the gauge of the new chain? What are all of the numbers off of the bar?

 

[Agent Orange]

Ok, I had my beautiful wife take a video, in the dark, with a flashlight, just after a scout meeting. I wasn't really dressed for cutting wood. I just wrapped up firewood last weekend, so the only log I had was this old piece of hackberry. It was certainly less than an ideal situation. I have the new chain on, I applied pressure and vacuum to the fuel line before I reassembled the unit. I also checked the tank vent out with my leak down tester to make sure that it is allowing fuel to flow. It seems to be cutting twice as good honestly, I am going to try and get a proper log to cut that will be a much better test.....more than just 20 sec of work anyway. I'm also going to tweak the carb settings a little after I get it good and warm, it might be almost where we want it to be now. It bogged down a few times, I never took my finger off of the trigger, it was always on full blast, unless I took it out of the cut. When the engine acceleration went up and down, that was because I was varying the pressure I was putting on the saw into the log, from none to about the weight of the saw, trying to get it to run normally. The last time I made a cut in the video shows how it normally bogged down all the time. The cut right before that the saw actually took off pretty good and I think it would have gone all the way through the log. The jury is still out in my opinion if this was my entire problem, but a new chain has certainly made a difference.

Video is private.

 

[isacguy]

Video is private.

Opps, sorry, let me try to fix that. Try it now.

 

[albert]

That saw seem lean. Starving for fuel under load. What is your H needle set at?

 

[isacguy]

I set it with a

That saw seem lean. Starving for fuel under load. What is your H needle set at?

I set it first by one turn from the bottom, like the manual stated on this saw, then I went lean until it accelerated, rich until it 4 stroked then set it back slightly on the rich side halfway between the two. Then I checked it with my tach at full throttle, 12900 rpm is what I was getting. It may need more juice like your say though, I need to get it out and really try to cut some wood with it and play with it a little more.

 

[albert]

Might just be set too lean or a restricted supply or vent. Might have an air leak. Metering lever too low. I would forget through tach for now and open the H 1/4 turn and retry.

 

[isacguy]

OK, I know it's been a long minute, but I finally got back to the saw. After all that messing around I was able to get the saw to run really well, as long as you were bucking with the saw. If it was turned on its side to fell a tree, it would cut in and out noticeably.

So in conclusion, a brand new carb was purchased, I picked up the older style that would fit on the 039, not the epa style that came with the MS 390. This took care of the problem of the saw cutting in and out, and a new chain took care of the bogging. Thank you again everyone for your help, I certainly appreciate it!