McCulloch 125 Decompression Valve/ Hard Pull

bplust · Jul 2, 2011

Hi All,

A few months ago, I started a thread asking for help with a problem with my 125. When choked, I can pull the starter cord, it pops off, but when I go to pull it once I open the choke, the decompression valve will close prematurely, regardless if the engine sounds or not. Anyone who owns this saw knows how tough it is to pull this saw over without the decomp pressed in; I've broken a cord or two, and I use the good kind, so it takes some pull to break a line, and apparently, even more to turn the engine over without the help of the valve.

My initial thought, as well as that of everyone who responded, was that of the decompression valve being bad. So, I tracked down a new one, put it in, and got the same result.

I can run the saw if I gently pull the cord a few times, put the piston just in the right spot, and then pull, but members of this site who also own this saw claim that this should not be necessary. And by the way, when this saw runs, it runs VERY well. It's nice to see a piece of equipment of this age running so nicely.

I asked a small engine shop owner who specializes in McCulloch, though has never worked on a 125, his opinion, and he felt that it was a good possibility that the timing was off, and early spark was causing my issues.

So, I have three questions:

1. What do people think about bad timing causing this?
2. How do I adjust the timing on this saw?
3. If people think that it isn't timing, what should I try?

Thanks in advance for any replies!

homelitejim · Jul 2, 2011

There might be a piece of carbon stuck in the decomp hole. I am not sure on how the starting mechanism is set up on that saw but is it worn or missing anything to get it to advance or retard the starting timing? Sounds to me like a gremlin. If the timing was off it wouldn't run very good if at all.

NORMZILLA44 · Jul 2, 2011

Sound's like a sore hand ouch! Some compression on that little guy LOL!:msp_biggrin:

bplust · Jul 2, 2011

A piece of carbon sounds like a good possibility. And the connection between the timing not being off because it runs so well makes perfect sense.

Here's another question:

If I clean the hole, there's a good chance that I'll push the carbon nugget into the cylinder. Is this a concern?

And Normzilla, you are correct. After experiencing this problem once, I started wearing my insulated winter mountaineering gloves which make my hands look akin to those of the Michelin Man. Ya, its got some compression.

Teddy.Scout · Jul 2, 2011

Slam in a 850 coil.
But that is a some work for no real gain.
Carbon sounds like a good place to start.

Side note,
On my decomps, it will release quickly!
A third hand would making starting some saws a lot easier for me!
Studded fingers are a result of LARGE CC CAD! I have and sure will be doing it again, hopefully note soon!

NORMZILLA44 · Jul 2, 2011

Yike's I can only imagine! Only saving grace is the weight for a drop start.:msp_thumbup: I think the small carbon pocket if that is it, and that I agree make's sense. Should heat up, and burn off if knocked loose. Dindn't see, may have been mentioned earlier, but did you get a good peek inside?

NORMZILLA44 · Jul 2, 2011

Guess with your'e bum leg, a kick start is out the question Matt huh? LOL!:msp_thumbup: How ya feeling?

homelitejim · Jul 2, 2011

It is a gamble, it could just blow it out the exhaust port or it could cause damage. If I were to clean it out I would pull the muffler and make sure the piston is at the bottom so when it falls out you can blow it out of the cylinder. I have a old homelite xl 12 that has a bent starting pawl, the saw was getting fuel, had spark and compression but would not start. I pulled the muffler and tried to start it and noticed fire on the exhaust stroke, of course I have not got it running as of yet.

rarefish383 · Jul 2, 2011

My best guess would be something like the carbon. As to the timing being off a hair. I put a NOVA II electronic module in my Homelite 1050 (100 cc) and all of a sudden the rascal got harder to start. The thing would kick back and rip your fingers off. No decomp to worry about. I asked a mechanic and he said those modules change the timing a little making it harder to crank, but when it starts it runs like that striped *** ape. So I do, as you said, and pull it over till I get it in the sweet spot and a short stroke will fire her up. I've gotten used to it. Just sayin the timing can be off one way or the other and still run good, Joe.

bplust · Jul 2, 2011

Just cleaned the hole up; didn't have any luck but I do have pain in my fingers now.

Teddy.Scout: How would an 850 coil help? I'm a bit of a newbie.

Thanks.

bplust · Jul 2, 2011

On a second try, IT WORKS! It was carbon, I cleaned a good amount out, prior to doing this, I moved the piston above all of the ports, and blew out the cylinder with the spark plug out.

We'll see what happens tomorrow, but for now, I started it 5 times, none of the starts causing me to start researching prosthetic hands.

Thanks everybody, it's been paining me quite a bit to look at that saw sitting on the shelf.

sawfun9 · Jul 2, 2011

I always push that valve in before every pull, just to make sure. Mine has a habit of popping out if I don't. And yes, I do understand your ouch. Been there done that, and don't want to go back.

Bill G · Jul 2, 2011

Hopefully you have got it figured out. If not pull the fan cover and check and see if it has a Nova/Atom or some other module. If it does your timing will be off and it is going to want to kick back hard when pulling it over.

Bill

dieselsmoke · Jul 2, 2011

Check your timing static, with a multimeter or a light. I measured and made a mark on the flywheel where the points are to open at 26 deg. BTDC.
A couple of degrees of advance will make it a mother too start, but run like a monster. All racers try to achieve max advance without detonating their motor.
On my ol 064, no decomp, I have to pull the starter rope to get just befor TDC, then pull like i mean it. Or suffer the ripped fingers effect.

RandyMac · Jul 2, 2011

I had a hot-rodded 797, no decomp, 3.5 degrees advance, with some port work. A miscue could cause damage.

rwoods · Jul 2, 2011

Randy, just where do you fall in the Clan Donald? Ron

RandyMac · Jul 2, 2011

A Sept of Clan MacDonald from Glencoe, also associated with Clan Gunn of the same region.
The name MacKendrick (Mine) is the same as Henryson or in Gaelic MacEanruig. The legendry ancestor of the Hendersons is Eanruig Mor Mac Righ Neachtan "Big Henry, son of Pictish King Nectan"
Anglo-sized to MacKendrick, then further degraded to Henderson (Henry's Son)

rwoods · Jul 2, 2011

Randy, read in the paper tonight that the highland games (the NC version) begins at dark July 7th. I sure there will be some stout lads there. Ron

Eccentric · Jul 2, 2011

NORMZILLA44 said:
Sound's like a sore hand ouch! Some compression on that little guy LOL!:msp_biggrin:

That ain't no little guy Norm. A 123cc high compression saw with a non-working decomp switch is a serious finger/rope/pawl/starter housing buster.....:msp_ohmy:

RandyMac said:
I had a hot-rodded 797, no decomp, 3.5 degrees advance, with some port work. A miscue could cause damage.

That must've been one mean sum##### Randy, both at the wood and on your hands...:msp_thumbup:

If it's not McCulloch it's CRAP!!!

YouTube - ‪All Things Scottish w/ Christopher Walken‬&rlm;

YouTube - ‪Let's get pissed!‬&rlm;

NORMZILLA44 · Jul 2, 2011

Good thing they are heavy, good for the drop starting!:msp_thumbup:

McCulloch 125 Decompression Valve/ Hard Pull

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