ms 310/390 idle issue

[birdhouse]

hello-
first post here.
i own a ms-310 that i've used for years and love. then i started reading on here and wanted more power. yes, i know i should just buy a pro saw, but that isn't in the cards for now.

i bought a 390 engine and put it in my 310 saw. got the complete sealed engine from baileys. i have also drilled out the exhaust. i put (one) 1/2" hole and (two) 3/16" holes in the small plate right outside the spark screen. screen is still there and in good shape.

i took out the plug on the "H" screw to get more adjustment and backed it out ~1.5 turns. the plastic plug seems to have no other use than a screw extension with limiters, so i never put it back in. "L" screw backed out approx 1/2 turn. new 85 octane gas with echo brand two stroke oil mixed a bit stiffer than 50:1 for the first tank. spark plug looks not black but not brown, somewhere in between. (after swap and screw adjustments)

i bolted it back together and she fired right up. but would not hold an idle. i figured this would be the case as a larger engine would take more fuel to idle than a smaller one. so i slowly started backing out the idle screw. left loosey gives more fuel correct? i got it to almost idle after backing it out a full 5 turns. this seems excessive to me but maybe not?

any thoughts on why my saw won't hold an idle? i did add the 1/2" hole to the exhaust while i was engine swapping, so maybe it's too much? i could weld it partially shut...

adam

 

[o8f150]

which carb did you put on it

 

[NewToStihl]

which carb did you put on it

Don't the 290, 310 and 390 all use the same carbs?

 

[o8f150]

I may be wrong but I think the 390 has a bigger carb,,, I know one of the stihl experts should chime in

 

[NewToStihl]

hello-
first post here.
i own a ms-310 that i've used for years and love. then i started reading on here and wanted more power. yes, i know i should just buy a pro saw, but that isn't in the cards for now.

i bought a 390 engine and put it in my 310 saw. got the complete sealed engine from baileys. i have also drilled out the exhaust. i put (one) 1/2" hole and (two) 3/16" holes in the small plate right outside the spark screen. screen is still there and in good shape.

i took out the plug on the "H" screw to get more adjustment and backed it out ~1.5 turns. the plastic plug seems to have no other use than a screw extension with limiters, so i never put it back in. "L" screw backed out approx 1/2 turn. new 85 octane gas with echo brand two stroke oil mixed a bit stiffer than 50:1 for the first tank. spark plug looks not black but not brown, somewhere in between. (after swap and screw adjustments)

i bolted it back together and she fired right up. but would not hold an idle. i figured this would be the case as a larger engine would take more fuel to idle than a smaller one. so i slowly started backing out the idle screw. left loosey gives more fuel correct? i got it to almost idle after backing it out a full 5 turns. this seems excessive to me but maybe not?

any thoughts on why my saw won't hold an idle? i did add the 1/2" hole to the exhaust while i was engine swapping, so maybe it's too much? i could weld it partially shut...

adam

There are several things that could cause your no-idle issue, but I would personally start with the basics. The muffler mod will make a difference in getting the saw tuned correctly, but I would start with the factory carb settings and go from there. With the H limiter removed you'll want to set it and the L to 1 full turn out from seated. This should get you very close to a proper idle. Also, don't forget about your LA (idle) screw. I can't say this for sure as I've never upgraded engine displacement, but it may need to be adjusted to compensate for the increased need for fuel at idle.

 

[AKDoug]

The 290 came with either an HD18D or HD19D, the 310 and 390 came with an HD21D.

 

[birdhouse]

wow- you folks are quick with the responses!
it still has the 290 carb on it.

the H and L screw are pretty close to factory, as i've never messed with them until the recent muffler mod. at that time i backed out the H screw 1/2 turn. then, during the engine swap i pulled the plug out and turned it out another full turn.

its the LA screw that i've been continuing to turn out (5) turns and still can't get it to hold an idle. it did seem to get a bit better as i slowly turned it out between starts.

adam

 

[NewToStihl]

H screw is your high jet - regulated fuel feed at high revs
L screw is your low jet - regulated fuel feed at idle
LA screw is you idle screw - does not regulate fuel, all it does is adjust the position of the throttle lever. Right increases idle speed, left decreases idle speed. From what you've said, I think you might be adjusting your LA screw in the wrong direction...

 

[birdhouse]

boom, nailed it! i have been adjusting the LA screw the wrong way!

saw is at my shop, but i'll adjust tomorrow and let you folks know!

thanks!
adam

 

[birdhouse]

after work today, i tightened the LA screw and walla! idles perfectly!

thanks again!

 

[NewToStihl]

That's very good news! The best fix is a free one...

 

[GrassGuerilla]

Keep us posted. Very interested to hear your impression as she breaks in. I'm betting they sell a ton of those kits.

 

[birdhouse]

i haven't cut any wood as of yet, but i'm heading up to my ranch for a long thanks giving weekend, it will get plenty of use then!

the kit went in very well. everything lined up as though it was OEM. the largest PITA was getting out the rear bar stud. i finally said screw it, and welded a nut on the end.

adam

 

[birdhouse]

that thing rips! i had a good check and balance as i brought along a friends ms-290 that is bone stock. had brand new chains on both saw. i was cutting pine, as it's about all i've got at my place. we have pine beetles killing the trees, so i drop the dead ones for fire wood. 24" at the biggest cuts.

anyways, the new 390 (310) with muffler mod and tuned carb was a night and day difference against a stock ms-290!!! the craziest thing is there was a 28" bar on my saw (390) and a 20" on the 290, and my saw still ran WAY harder through the cuts. i know, i know, 28" is too big for that saw, but it save my back as i can cut from the hip a bit more and extend my arms less. i just mix some motor oil in with my bar oil so its thinner and the pump can keep up with the long bar.

ear to ear smile the whole weekend!

adam

 

[banana boat]

Just a complete side note nothing to do with your issues but I have to ask why 85 octane fuel ? Why not use super for a little added protection against detonation especially when your unsure about the saws tune.

 

[birdhouse]

banana boat- because up at my ranch i've got a diesel excavator, a diesel genset, three gas gensets, chainsaws, fourwheelers, dirtbikes, ect. i have to continually bring gas cans with stabilfuel in them. just one more thing if i have to get "special gas" just for the saw. and honestly, i've never had a single issue, even with the ethenol stuff. i've run gallons of 1 year plus old gas with stabil through my 310 and never had a problem. my place is offgrid. nearest gas station is 1.5hours away.

don't mean to sound cranky about it, but that's why.

adam

 

[exSW]

banana boat- because up at my ranch i've got a diesel excavator, a diesel genset, three gas gensets, chainsaws, fourwheelers, dirtbikes, ect. i have to continually bring gas cans with stabilfuel in them. just one more thing if i have to get "special gas" just for the saw. and honestly, i've never had a single issue, even with the ethenol stuff. i've run gallons of 1 year plus old gas with stabil through my 310 and never had a problem. my place is offgrid. nearest gas station is 1.5hours away.

don't mean to sound cranky about it, but that's why.

adam

Lucky so and so

 

[banana boat]

I hear ya Adam i just figured around here there is less than a 10% difference in price between the lowest and highest octane pump fuel (too dam expensive either way lol) so for me I just run super in everything I have, but to each there own

 

[birdhouse]

banana boat-
yea, i should probably change when it comes to the saw. most stuff i use is AOK on 85. so it's more of another can, and or tick list item. i usually have to stop quite a bit on the drive to pick up a bunch of specialty items for all sorts of other purposes. since i've never had issue with 85, it's just is never on my radar. when the saw was new i ran premium, and i still run fully synthetic stihl oil for mix. that's easy as a 1 gal premeasured 6 pack will last quite a while, and i usually buy those two at a time (12). with a three hour drive to my place (bickleton, WA) without stops, i'm usually itching to get out there as the materials stops continue. i am continually amazed at what stabil fuel is capable of! i put that stuff in about everything except my truck!

adam