Longest bar on a Stihl MS390?

[a. palmer jr.]

That's true, it is plastic.

With the muffler mod, I presume the main outcome is less backpressure and more RPM?
Wouldn't that cause the sprocket to turn faster and possibly outpace the fixed output ouler?

I'm not sure about that. The sprocket turns faster and that turns the oiler worm faster also. I would think that would result in more oil unless it's restricted somewhere..

 

[a. palmer jr.]

In a 2 stroke engine, the very basic scavenging process of a chainsaw is not so simple.

The back pressure created by the muffler keeps most of the fresh air/gas from exiting out the exhaust. Open it to much and your performance will suffer. How much is that, is not simple to answer.

You're correct, that's why the high performance motocross bikes use an expansion chamber to kinda re-burn the fuel that would normally be lost out the exhaust..

 

[Wood Doctor]

We don't even run the 25" on the 390. Mainly due to the fixed output oiler.

I also tried running a 25" hard nose bar on a 390. It got hot and could not pull it. Fixed output oiler was probably the culprit. So much for that. Perhaps it could pull a 25" sprocket nose bar, but I save that bar for my MS361 and 046 Mag. Big bars belong with big saws. The 390 reminds me of "the little engine that couldn't quite."

 

[Overkill338]

,,

I'm not sure about that. The sprocket turns faster and that turns the oiler worm faster also. I would think that would result in more oil unless it's restricted somewhere..

The only way to get more RPM is to lean it out. Performing a muffler mod and not tuning it will cause it to turn a little higher. But that's no where close to being a good thing.

 

[kenton.a.frank]

I was thinking the same thing. You can open the muffler up and take epa stuff out and return it but you really shouldn’t run any higher RPM unless you want to burn it up.


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[Overkill338]

I was thinking the same thing. You can open the muffler up and take epa stuff out and return it but you really shouldn’t run any higher RPM unless you want to burn it up.


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If you want a 390 to turn more rpm and run a 25" bar, then just get a 360/361/362.

 

[kenton.a.frank]

If you want a 390 to turn more rpm and run a 25" bar, then just get a 360/361/362.

Agreed.


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[Ryan'smilling]

If you want a 390 to turn more rpm and run a 25" bar, then just get a 360/361/362.

Agreed.


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I mean sure, a 361 is a better saw for sure. No question about it. But if the OP has a 390 that has been a good runner and he occasionally needs to run a big bar, the 390 can probably do the job. My friend ran one with a 24" bar in Washington for a few years until he got CAD and sold it in favor of a selection of pro saws.

 

[lambs]

I wouldn't go over 20" of bar if the 390 is to remain stock. My 039 does ok with 20", but I'm running 18" on it most of the time. But I'm used to running an 046 with a 20" too.....

 

[a. palmer jr.]

I did the muffler mod on mine and richened up the carb a bit and run a 20 on it. I don't advocate anyone trying to run a saw too lean unless they like to rebuild them..I have two saws with longer bars on them, a Homelite 924 and a Husqvarna 372XP.

 

[kenton.a.frank]

Ok here’s the deal. There will always be an eternal debate on what a saw can pull and what it should pull. The 390 with a little novice work can pull a 24. Sure it won’t oil like a 362 or 460 will obviously for a couple reasons. One being it is a homeowner grade saw and two bring it really should top out as a 20in bar saw. If tuned right it will pull the 25 and not do a huge detrimental impact to the life of the motor, however the bars life, chains life, and clutches life will probably be slightly shorter than it it was on a larger or pro grade saw.

Still in my opinion if someone is asking “what’s the longest bar for a 390” I will still say 24-25. It would still be within reason to not be in my opinion abuse. However if you have a clean 390 and need a 25in bar. I’d post the 390 for sale and try to find a tried and true 044 that runs well and hope it comes with a 25in bar. That way you have more than enough power and piling capability. And probably only shell out the amount of a new 25in bar and a few chains different.


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[Overkill338]

I will say I'm not throwing off on the MS390. Its 64cc and it acts like it! They are very durable and torquey!

 

[drf255]

It’s got one of the most pathetic muffler outlets I’ve ever seen. If you don’t open under the baffle, the noise increase won’t be that much.

Do the muff mod, if anything, to keep the saw cooler running.

 

[wyk]

25 max in my opinion.


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I've tried a 25 on a 390, and it pulls it well enough, but it didn't oil it enough for me to be comfortable using it. So keep an eye on that.

 

[Cope1024]

if you decide to go 25", I have a new Stihl ES bar and two new chains in the Trading Post. Mine are .063 though.

 

[ssm1699]

I ran a 25 on my 390 and it pulled it just fine. My oilier, of which is a stock pump that is turned all the way up, kept up with it just fine. I also have my muffler modded and my carb tuned richer. I definitely noticed a difference when I did the muffler mod and re-tuned it. My biggest suggestion would definitely be to run a skip chain on it, as I did. I had it buried in hard maple and pulled it just fine. It was definitely not a speedy cut, but it did it. Just my .02 and personal experience.

 

[jltrent]

I have had 4 MS390s and I remember one that would do 165 lb compression. I put a 25" bar with a full skip Stihl non safety chain on it. Maybe not a logging saw, but for occasional use I thought it did fine. I couldn't tell much difference from a MS440 unless you really leaned into it. Very little difference in a MS390 and MS361 as I have had several of both and even the specs says so. Probably the one with the best chain will cut the best.

 

[MS460WOODCHUCK]

It is complex. Power is not always faster. And engines often need backpressure to work properly.

What IS true, that "Louder seems more Powerful", and it might only seem that way. Which is for most, all the justification needed. Imaging the doey eyed and jealous envious looks of your fellow cutters as you are twice as loud then even their bigger saws.

Whatever...we are not taking the front cover of the muffler off and running it.

Have you ever looked at the exhaust port of a 290, 310 or 390 and then looked at the opening in the muffler? Huge difference in them and the dang saws are set up lean lean lean from factory taking life and power away. It's not rocket science that the cover opening size is maybe 25% of the exhaust port size of the cylinder and that is not near what it needs to be.

To the original poster just open up the couple TINY holes behind the deflector of the muffler and then open the deflector up where exhaust exits also and you my friend will see that alot of people on here are full of it. I have personally modded these series of saws mufflers at least 30 times and they love it!

 

[MS460WOODCHUCK]

In a 2 stroke engine, the very basic scavenging process of a chainsaw is not so simple.

The back pressure created by the muffler keeps most of the fresh air/gas from exiting out the exhaust. Open it to much and your performance will suffer. How much is that, is not simple to answer.

Have you ever heard of a 440, 460 or 660 dual port muffler? If not I suggest you look into and try one on any of these saws if you have ever or do own one of them. These series of saws 290,310 and 390 are choked up just as bad if not worse than the pro saws?

 

[MS460WOODCHUCK]

I also tried running a 25" hard nose bar on a 390. It got hot and could not pull it. Fixed output oiler was probably the culprit. So much for that. Perhaps it could pull a 25" sprocket nose bar, but I save that bar for my MS361 and 046 Mag. Big bars belong with big saws. The 390 reminds me of "the little engine that couldn't quite."

Wow, the 390 is bigger than the 361. At least the ones I have owned.