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Author Topic: Rebuilt MS290/ MS390 fine tuning 'dialing it in'  (Read 813 times)

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Offline motzingg

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Rebuilt MS290/ MS390 fine tuning 'dialing it in'
« on: May 13, 2022, 03:40:01 PM »
Long story... long, I picked up this ms290 that was being thrown away by a lawn care company a couple years ago. It was run hard and totally thrashed but I had it running in about 20 minutes with a new fuel line so i figured what the heck, put a cheap 20" B/C on it and use it for cutting down rotten trees, stumps, fence line trees with nails in them.  I have a small hobby farm and some nicer 50cc saws that see a lot of use on smaller stuff, but usually once or twice a year i have something thats big and ugly and its nice to have a big dirty saw for those jobs, and if i drop a tree on it no biggie.


Got the cheap china B/C and some missing parts, but it felt weak so I grabbed a china 390 jug thinking it was wore out.

Rebuilt it with the china jug and some OEM parts, still didn't run right, found out it needed a 390 main jet so i ordered that, waited, lost it, ordered it again, found the one i lost.... blah blah blah. 

2 years later, its finally reliable enough that its worth dragging out into the field, I used it last week to cut down 4 crappy weed trees and sure enough a squirrely box elder took a roll and warped the bar. Lucky it was only 12 bucks. I managed to get it bent back pretty good but you can tell that its cutting a hair-off.

Now that i'm running it a bit, its not as terrible as i've thought.  Heavy, and i don't like how it balances with the chitty 20" b/c, but its got a lot of torque and it actually does a nice enough job that it might be worth dragging it out to buck firewood. That said I'm ready to put a little time and money into making it nice (er).

All told i've got less than $100 into the saw and the most expensive thing was $55 for the two oem fuel/oil caps! So i don't mind throwing a few bucks at it to get it to do the job of a poor man's 380. My buddy has a really nice 038 with 20" b/c, specs say the 390 is 4.6 hp and the 380 is 4.9 but his saw seems like it goes through wood about twice as fast.

1) first thing it sounds like is i need to do the muffler mod.  Reading what some folks are saying, it definitely feels 'choked down'... it doesn't really rev out and the WOT 'no load' speed doesn't pick up as it goes lean.  I'm hoping the high rpm torque improves considerably, right now it feels like it drops off really quick in the cut but then maintains torque at a lower RPM than what i would like.  I noticed when i've modded other mufflers, it seems to pick up the rpm of the torque peak a little bit, and this dog needs it badly.

2) Is a 20" bar too much for this saw? I see a lot of 290's fitted with the 20, so i don't think i'm being greedy.

3) Is there a chain that would be a better choice?  Narrower or more efficient? I was thinking just going with the basic Stihl Rollomatic and rs3 maybe?  Given my usage i'm open to suggestions. I know almost nothing about chain and bar selection. I think the china chain i bought was a semi-chisel, its a little bit grabby but i only use this saw for bigger stuff so it doesn't really bother me, but as a weekend-warrior i'm always a big fan of safety.

4) is there anything else that i could/should do tuning wise? advance timing?  any other carb changes i should have made.  I think my tune is pretty well spot on at this point but haven't checked the plug after about 4 tanks of gas through this setup.  The low speed screw doesn't do much between 3/4-1.5 turns, it dies below that and above that, otherwise i have the idle a bit on the high side or it kills when it comes down quick from WOT, which i don't like because its kinda dangerous IMO. 

Thats about it, any other tips or tricks to get this $100 trash picked plastic saw to do the job of an $800+ saw would be greatly appreciated.

Offline Guydreads

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Re: Rebuilt MS290/ MS390 fine tuning 'dialing it in'
« Reply #1 on: May 14, 2022, 04:41:35 PM »
Ok. First of all, congrats on getting that saw running good!

Muffler mods can always be done to any saw. It'll improve high end torque, and it will also give you throttle snap.

20" IMO is definitely not greedy at all. I don't have one but I think 390s can run up to 24"

A full chisel chain is gonna be a lot better, with no real cons that I've noticed as far as safety. It's a bit hungrier, so you might want to stick to 20". 

Offline motzingg

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Re: Rebuilt MS290/ MS390 fine tuning 'dialing it in'
« Reply #2 on: May 18, 2022, 05:26:02 PM »
well not much traffic, long post... boring topic... what can you expect.

I guess i'll just go grab the basic stihl b&c combo

also noticed last week that the oiler seems to be kinda intermittent. not sure if thats from the bar not lining up great or if the pump is jacked.  I took it all apart and cleaned it up and it appears to be pumping with the bar off but even at full flow its not putting a lot on the chain, which most of my other saws if you turn them up all the way are a straight geyser. 

Add it to the list, spend more money. If the bar is dry as dirt that definitely makes it a lot harder to pull, explains why it was dragging in the cut. 

Offline Fishnuts2

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Re: Rebuilt MS290/ MS390 fine tuning 'dialing it in'
« Reply #3 on: May 19, 2022, 08:10:16 AM »
I had an 029 converted to 039 that ran pretty good.  Take the deflector off the muffler and enlarge the exhaust outlets plus add some more holes on the top and side of the muffler area that lies Under the deflector.  I didn't mess with the depressed area in the front of the muffler body as that makes them really loud.  Open up the last part of the deflector so the exhaust goes straight out to the side.

Take a points file and file the flywheel key back on the counter clockwise side to advance the timing a few degrees.

It would run right with, or a little ahead of my stock 036 Pro after these simple mods.

Offline motzingg

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Re: Rebuilt MS290/ MS390 fine tuning 'dialing it in'
« Reply #4 on: May 20, 2022, 10:21:05 AM »
Thanks for chiming in fishnuts, I've gotten a lot of good info out of your posts over the years so that goes a long way.

I found an image of the 'european' exhaust deflector the other day, sounds similar to what you're talking about.  My plan is to just widen the holes and add the second row of holes and leave it alone.  If it tunes up and runs good after that, i'll advance the timing, one change at a time.

If i could get this thing to run like an 036 i would be very happy.  Its too heavy and awkward to be my go-to saw, but at least if it runs hard with the 20" it will earn its keep. 

Offline JD Guy

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Re: Rebuilt MS290/ MS390 fine tuning 'dialing it in'
« Reply #5 on: October 12, 2022, 04:11:20 PM »
Interested in how things turned with your 290/390 project or if you gave it the boot :D

I have a pretty old 290 that still runs ok but thought hard about getting it to 390 status. 

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