3120xp lost power in cut, tough to start ? Troubleshoot.

[andy]

Hoping you guys can help me avoid sending this guy in to the shop (which is not nearby).
I'm not much of a wrench but can do basic stuff and have reasonable tools here.

This saw has been really great for me but yesterday it acted up for first time.
Things to know..... It's been Ported by Randy, MM done, Also has High Circuit installed on Carb. I was running 40:1 truefuel so 92oct.

The Saw was sputtering and then quit while in a milling cut.
It then became difficult to start although, I was able to start it by holding the throttle on while pulling it over.


I checked the Plug... used but clean.
Also took out Air filter and gave it a good cleaning.
The fuel PU filter is not very old. If it's lacking fuel wouldn't it wind up rather than loose RPM's?

The Saw is set to Low 2500 as per factory and the high bounces on my wired tac between 11500-12000.... great for milling.
The T screw seems like it needs a lot of rotation to make a difference... unlike my old 288 which was very responsive.... different carb and whatnot.

Where should I go next ?

Thanks for replies.

 

[Jacob J.]

You need compression, fuel, and spark. Is the compression still good? Where are the high/low screws at as far as # of turns out?
Still getting good spark? Any kinks in the fuel line?

If it were starving for fuel it wouldn't necessarily wind up - winding out is a sign of an air leak.

 

[huskihl]

Take the muffler off and check the piston for scoring. Although it sounds more like its rich than lean. The H screw may have backed out while running. The spark plug may be shot too

 

[andy]

Thanks for the replies.
OK, I'll check fuel line/filter and look at piston.

The T screw has very little tension in it... is it spring loaded?
Should feel tighter yeah?
I did a factory set for the L screw and then adjusted with a tach to 2500. (closed it down then one 360* turn open etc..)

Although I mill with it, it's relatively low hours saw and stays pretty cool. (maybe 30-40hrs tops run time).
Hard to imagine P/C or compression issues at this point.

USE.
I usually run one rip at 12'-16' length x 20-30" wide in cedar or Hemlock (softwoods).
The saw gets a good cool down idle before I shut it off and move the plank before the next cut.
It's not cooking through rip after rip etc...have never thought it was hot.

I mention running up from loss of fuel as my String trimmer winds when I get to the end of a tank without noticing fuel getting low.
The 3120 never gets that chance to run dry as I top both fuel and oil after each rip. (tanks at 1/2-1/3 remaining after each cut.

 

[Jacob J.]

What do you mean by T screw? Is that the screw that Randy used when he made the carburetor fully adjustable? If so, that would be the "high speed" screw.

For milling, you want a saw set slightly richer than for normal cutting. I would roll with the L speed screw set at 1 1/6-1 1/8 turns out (counter clockwise), then
use the idle screw to set the idle at around 2700-2800 rpm.

Milling is some of the hardest work a saw can do. I prefer not to use modified saws for milling. I just use the largest stock saw I have available.

 

[andy]

T screw is the throttle position if I understand correctly.
L is low speed air/fuel mix and then T is for how much throttle is applied at no touch idle position.

The high is another screw Randy installed above the T screw.

I’ve been trying to keep low mix at 2500 and high at 12k or slightly below.
So yeah... a bit rich but not super.

It’s my only big saw so.... gotta go with it. Maybe a stock saw would be better.

I just set Idle to 3000 and it starts better.
Clutch still does not engage to spin chain until around 3800-4000.
My chain is just right. Barely hugs bar and can be pulled around by hand.

Thanks for the exchange Jacob.... It helps.

 

[Jacob J.]

Ok - I gotcha on the T screw - yes, they're usually backed with a spring for tension (depending on which carb you have).

I'll go out and check my 3120 carbs shortly.

 

[andy]

It’s gonna need some carb work.
The T-screw spring is out of tension.
I was able to finish my log but by the time I was done, the idle was way up into chain spin land.
The screw drifts from vibration both up and down.
Something else also seems amiss as it acts up when the saw is laid flat into milling position. Some junk in the fuel system maybe.

All good... gotta find a local shop and just let someone who does this everyday get it right.
Gonna stay in my lane on this one.
Thanks for the help.

 

[Deleted member 117362]

Pull your muffler and show us a pic, sounds like you smoked it.

 

[lone wolf]

Take the muffler off and check the piston for scoring. Although it sounds more like its rich than lean. The H screw may have backed out while running. The spark plug may be shot too

Plus 1 on that.

 

[WidowMaker_1]

Toasted it

 

[andy]

It’s gone. Now where is that damn shovel?

 

[WidowMaker_1]

It’s gone. Now where is that damn shovel?

It will need a square hole, being like a box and all

 

[andy]

It will need a square hole, being like a box and all

Yeah it’s a cinderblock without a doubt!

 

[Deleted member 117362]

No hole or shovel needed, just a rebuild will work.

 

[Brent Nowell]

We need a baseline to start with, two others suggested pulling the muffler and taking a pic, I third that

Intake bolts a notorious for vibrating loose from factory, at least they were loose on three of my saws. Your doing everything right in terms of fuel/oil, the idling to cool it down, text book good practice. But if you had an air leak all of that doesn’t mean squat for saving the engine.

Sputtering in the cut is a classic sign of compression loss, but we won’t know anything till you pull the muffler.

 

[andy]

You’ll really want to see that piston for real or are we joking around?
Compression feels really strong on this saw.
Pulling it over without the decomp is like when I got it.... unfriendly work.

 

[pioneerguy600]

On milling saws a lot of pistons get overheated and score, its one of the most often causes of loss of power and hard restarts so yes its best to check the piston, it only takes a few mins to remove a muffler and then one knows for certain.

 

[andy]

Thank you guys for taking the time to check in.

Here are piston pics.
No scoring below the ring... a bit of old work evident above the ring.
There is a lot of oil and fuel in here that's for sure.
I don't have a compression guage...Doing the ole pull cord drop takes about 10secs for the saw to drop... lots of compression.
The last pic is big if you click on it to look at that area above ring.
Would you mess with that piston ?
Thanks as always for replies.

 

[pioneerguy600]

The piston looks good enough to continue using it, thanks for posting the pics.