The SP 125 lives.. now how do I tune it up

AKDoug

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The SP125 that I was getting advice for a few weeks ago is now running. I put new seals in it and my son and I reassembled it for a Christmas project. I cleaned the carb (it looked pretty good) but I didn't have a rebuild kit for it. The reeds look like they are in great condition and the saw has 175# of compression. The saw starts easy, idles fine, revs up pretty good, but it sure feels like it's running rich on the top end. I know the older saws just don't rev like the new ones, but this thing really doesn't feel too powerful on the top end. It has a Tillotson HS 124A carb on it.

Here's a video of it running. It's -16F and thats the only log I could get to in the snow. Any suggestions on how to clean the top end running a bit.

[video=youtube;cbR2bXkhXSQ]http://www.youtube.com/watch?v=cbR2bXkhXSQ&feature=youtu.be[/video]
 

leeha

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The SP125 that I was getting advice for a few weeks ago is now running. I put new seals in it and my son and I reassembled it for a Christmas project. I cleaned the carb (it looked pretty good) but I didn't have a rebuild kit for it. The reeds look like they are in great condition and the saw has 175# of compression. The saw starts easy, idles fine, revs up pretty good, but it sure feels like it's running rich on the top end. I know the older saws just don't rev like the new ones, but this thing really doesn't feel too powerful on the top end. It has a Tillotson HS 124A carb on it.

Here's a video of it running. It's -16F and thats the only log I could get to in the snow. Any suggestions on how to clean the top end running a bit.

[video=youtube;cbR2bXkhXSQ]http://www.youtube.com/watch?v=cbR2bXkhXSQ&feature=youtu.be[/video]


Your biggest problem is the Tilly HL fixed high speed jet.
With those 125's with this carb you really need to load
the saw and you can't do that in that pecker pole your
cutting. Put that thing in some real wood and load it up
and she should clean out and cut. If not the metering
lever may be a tad high and you can try lowering it. The
best would be to find a Walbro SDC carb for it as they're
fully adjustable. Hope this helps.


Lee
 

leeha

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Just watched the vid again. Your getting alot of smoke.
You could be sucking bar oil and it also sounds like it
could be skipping. Did you do anything with the points?





Lee
 

AKDoug

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Just watched the vid again. Your getting alot of smoke.
You could be sucking bar oil and it also sounds like it
could be skipping. Did you do anything with the points?





Lee
I pulled the ignition to put in the seals. I reset them at .020" gap at TDC. Much of the smoke is a result of the super cold temps and the breath of my camera kid. This video is the same way, lots of breath steam. The one adjusting screw is set at 1 1/4 turn out.

[video=youtube;GEhzd0wnWf8]http://www.youtube.com/watch?v=GEhzd0wnWf8[/video]
 

AKDoug

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BTW, no big wood available until it warms up. My excavator sure doesn't want to start in these temps :D
 

Yukon Stihl

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BTW, no big wood available until it warms up. My excavator sure doesn't want to start in these temps :D

Do you get any real big wood up there?
Here big is 36"-44",don't think that i have ever seen anything over 4' around here.
 

AKDoug

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24" birch is big wood up here. There is a 20" piece in that pile, but until it warms up I can't dig it out.
 

Eccentric

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I only heard it clean up once when under load in the wood (and only then for a brief split second). At least you're not going to burn it up that way. If you're going to keep that Tillotson HS carb then you should put a kit in it. Otherwise, an SDC20 is in order. Until you find an SDC..........look inside that HS again (while putting in a kit) and read the # stamped onto the high sped jet. Look at those part #'s I gave you on AS and see if you can find the next 2 smaller jets. Bob Johnson or Discount Marine (or Tillotson) may be able to help you.

Find some bigger wood to cut as well. If you're not going to get into anything over 24" then definitely run a .404-8 rim. That saw will run a 36" bar with a .404-8 rim without much difficulty, although I prefer a .404-7 when going over 30" to help the clutch live longer. Your saw also did sound like it was missing (as Lee mentioned). Make sure the kill switch, points, and condensor wires aren't grounding/shorting out).
 

AKDoug

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I disassembled the carb today. It looks like I have a .030 high jet. It sure appears that it is pressed in. Does anyone have any advice on how to remove it? I think I've located a .028 jet and that may help my issue. I will look for a .029 main first, as I know better than to take two steps on jet size. I'm still on the lookout for an SDC-20, but that may take a while. Are there any adjustable Tillotsens that have a same sized venturi that I could modify to work?
 

Eccentric

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I disassembled the carb today. It looks like I have a .030 high jet. It sure appears that it is pressed in. Does anyone have any advice on how to remove it? I think I've located a .028 jet and that may help my issue. I will look for a .029 main first, as I know better than to take two steps on jet size. I'm still on the lookout for an SDC-20, but that may take a while. Are there any adjustable Tillotsens that have a same sized venturi that I could modify to work?

There was also a Tillotson HS (HS70A) that was used on some CP125's (those that weren't equipped with an SDC20). The CP125 was the model before the SP125.
 

AKDoug

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The jet, just as I thought, presses in. I drove it out with a brass punch and put in a new one that was two sizes smaller. The saw runs great, it was running a little fat, so I'm happy. I'll back to the old jet when it comes time to run a bigger bar.

[video=youtube;AA4K_qb9bgA]http://www.youtube.com/watch?v=AA4K_qb9bgA[/video]
 

AKDoug

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That's my 17 y.o. son. He throws that thing around pretty good. The only chain I could find for it was .404 Stihl RM skip tooth. I think it would cut way faster with RM full comp. It outruns my Stihl 441-CM through that log by about 4 seconds.
 

Eccentric

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Sounds MUCH better.:thumbsup:

With that sized bar and wood, full comp .404 and a .404-8 sprocket would speed things up. It's probably tuned about perfect for that increased load too.
 

Al Smith

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I think the biggest problem is that fixed jet carb .It started to clean up a couple times but there wasn't enough log there to put the big boy under a load .

20 thou on the points is close enough,they call for 18 I think .20 would probabley bump the timing about 1.5 -2 degrees all things considered .
 

AKDoug

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Al- could you walk me through the points setting procedure on this saw?


Sent from my iPhone on tapatalk
 

leeha

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Al- could you walk me through the points setting procedure on this saw?


Sent from my iPhone on tapatalk


I know i'm not Al,
But setting the points is very easy.
Mcculloch wants .019 to .021 gap.
So position the crank so the points
are full open and gap to spec. I gap
all my Mac's to .020 to .021 because
most times i'm installing new points
and they will tend to close up a hair.
If your at .020 you'll be fine.




Lee
 

Al Smith

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You can play with it a little bit .Factory specs say 26 degree advance but usually a couple more makes them scoot a little better .I have one with a 2.5 degree offset key in the flywheel combining it with a tad wider on the points probabley has the timing up to 28-29 degrees . Enough it runs good but not enough it tries to pull your fingers off when you start it .It will kick back every so often though .

There's a guy on Magnus site just recently that has a vid clip of a Mac gear drive under load .It's tuned to perfection .It has about the correct sound the thing should make if in good tune .I've got one too but I'd have to resubmit it to U-tube or something because I forgot which vid posting site I had it on .
 

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