McCulloch Chain Saws

[dieselsmoke]

Hey Kyle, in a pinch you could rob the guide plates from your newly aquired 250. Same large mount style bar IIRC.
Get that sucker runnin then work out the details. IE: bar, chain, guides ect.

 

[promac850]

Hey Kyle, in a pinch you could rob the guide plates from your newly aquired 250. Same large mount style bar IIRC.
Get that sucker runnin then work out the details. IE: bar, chain, guides ect.

That's what I'm planning to do...

Soon... possibly tomorrow.

 

[Eccentric]

Kyle, they look a little strange to me but are these the plates you need? MCCULLOCH CHAINSAW 125 795 895 GUIDE PLATE STBX635 | eBay Ron

This one is the inner plate for the big Mac geardrives.
840,890,895 and probably many other models. At least
thats what it looks like to me.



Lee

That plate is indeed the inner plate when used on the big gear drives. It is the outer plate when used on the direct drive saws. The inner plate for the DD saws is a mirror image of that one. I can post the mac # for these plates later. For some reason, the outer plate is cheap on feebay, while the inner part # is three X as much........from the same sellers...

Note that those plates will only propperly oil an earlier style large frame Mac bar. The later style large frame Mac bars which look like enlarged 10-series bars (they oil through the adjuster holes, and have no seperate oiler holes) require the later style bar plates. These look like enlarged 10-series bar plates, and are symetrical. One part # is used on inner and outer. You must match bar and bar plate types if you want the chain to be oiled...


Edit:

-McCulloch's part number for the 'old style' left side (inner for a DD saw) bar plate is 61995.

-The # for the right (or outer on a DD saw) is 61996.

-The number for the left and right SET of plates is 61994.

-The number for the later style bar plate (which is the same for both left and right as the plates are symetrical) is 64935.

 

[Ambull]

I got this Super 250, it runs good, but not perfect. It has a McCulloch carb with the choke. Choke works great, no need to prime when starting. At idle, the saw hunts between 2700-3000 RPM. The throttle linkage is not directly connected to the throttle arm, and the throttle hunts between the linkage and the idle screw. At around 2800 RPM, the clutch engages, so the chain is spinning almost all the time. If I hold the throttle against the idle screw, it will stall. There is a spring on the throttle arm that seems to not be properly connected. At WOT, the motor stop 4 stroking at about 9800 RPM, so I adjusted the H screw for about 9500 RPM.

So here are my questions:

1. Is the throttle spring supposed to hold the throttle against the idle screw, or the linkage?
2. There are ratchets on the throttle arm to tighten the spring. How tight should it be?
3. Is the clutch pulling in too early? I am thinking that it is.....
4. Is 9500 RPM typical for the high end? Seems a bit slow to me.

 

[dieselsmoke]

Ambull, Mcculloch's governed Idle llinkeage, when you get them sorted out they work good. ON the other hand they can be a pain to get to that point. In theory the intake impulses work against the spring loaded throttle butterfly, so that the throttle opens when the RPM's fall off. That's the theory.
Got my S250 to idle so perfect with that carb, it idles for a while then it blips the throttle instead of dying out. But my 790 I NEVER got sorted. It idles way to high. I played with the spring tension and low needle settings till I just plain got tired of messing with it. You will see the tiny spring and a small diameter disc shape with notches, just inside the throttle link. one end of the gov. spring hooks to a notch the other against the carb body. It's trial and error to get the spring tension just right. And the low mix adjust just right, and the throttle stop controls the range that the throttle can swing ...... All i can say is start early some morning when you have maximum patience, and go for it, and good luck .:bang:

 

[Eccentric]

Ambull, Mcculloch's governed Idle llinkeage, when you get them sorted out they work good. ON the other hand they can be a pain to get to that point. In theory the intake impulses work against the spring loaded throttle butterfly, so that the throttle opens when the RPM's fall off. That's the theory.
Got my S250 to idle so perfect with that carb, it idles for a while then it blips the throttle instead of dying out. But my 790 I NEVER got sorted. It idles way to high. I played with the spring tension and low needle settings till I just plain got tired of messing with it. You will see the tiny spring and a small diameter disc shape with notches, just inside the throttle link. one end of the gov. spring hooks to a notch the other against the carb body. It's trial and error to get the spring tension just right. And the low mix adjust just right, and the throttle stop controls the range that the throttle can swing ...... All i can say is start early some morning when you have maximum patience, and go for it, and good luck .:bang:

Brad's got it JP. Trial and error. Also, if you alter the L side tune enough, you'll have to square away the 'idle governor' spring again afterwards. When it's all 'right'....the engine will hunt slightly at idle, but won't die. The chain will usually stop, then move a tad.........then stop.......then move a tad.......etc. Shouldn't be constantly moving, and shouldn't be moving fast.

 

[Eccentric]

Here's the 'manifesto' I wrote on large frame McCulloch bar mount patterns, bar plates, and the resulting compatibility/oiling issues:

http://www.arboristsite.com/stickies/71126-1008.htm#post3689465

http://www.arboristsite.com/stickies/71126-1008.htm#post3689491

 

[bob15]

SDC carb question

I just bought three brand SDC 44 carbs (PM10-10s PM700, PM7-10) for under $35 a pop(not really sure why :msp_unsure. This carb has the long extensions for the low & high adjustments (not having to remove the air filter for adjusting). My question is (I haven't had the time to visually compare), what's the difference between the SDC 44 & 38A? The 44 was used on the 700 and the 38A on the SP70. Both have external idle adjustments. Bore size different?

I cannot see in my mind where if I was desperate, i could swap out....


bob

 

[rwoods]

Kyle, I think you need MAC 61994 for that MAC branded bar you have. As noted by Aaron this is the pair. So just run down to you neighborhood MAC store and pick up a set. If you look real close you can see that my only spare set retailed for $5.85. It is also labeled with "P/N 61994 USE WITH: STANDARD MAC BARS".

View attachment 245480
Ron

 

[promac850]

Aaron, those are good write ups, thanks for the links.

Ron, those are the plates I need. (or I can modify the bar, but I won't if I can help it by getting the right plates)

As for the 790, it pops, but will not run. I've pulled it over somewhere around 150+ times. So many that I lost count. It popped with the fault back carb, and popped with the Tilly carb. I switched to the Tilly to see if anything changed. Nothing, it pops but won't frigging run.

I even had my dad hold the thing to the ground while I pulled it over real hard with two hands on the recoil handle. It sputtered three times in a row, then nothing. Can't hardly type with my right hand now, much less try holding an object.

 

[Eccentric]

Kyle maybe your point gap (and therefore timing) is off.


If you're unsure what bar plates you need, post a pic of your bar tail.

 

[heimannm]

I did arrive home late last night, today was mostly going through the motions but I did get a few chains from the last big score cleaned up, sharpened, labled, and put away. Started cleaning up a PM850 I picked up quite a while back. Saw had no compression so I figured the piston and cylinder were toast, turns out the piston was broken (I will post some photo's when I get the computer fired up again). I just happened to have one of the correct NOS pistons on hand and since the cylinder did not too bad I decided to give it a try. Seems to only have 130 PSI compression, maybe I will try a different compression release valve tomorrow. In any case I will get it together and (hopefully) running this week just to see what it is like.

This one was supposed to be an organ donor for Stude54 (needed a fuel tank) but I guess I will have to find another for him since I don't have an 850 in my line up yet and this one should at least run.

Anyone have a muffler that will fit an 850? If not I may have to take a lesson from Ron and make an adapter to fit some older type muffler. The 850 is different from the smaller 10 Series, and different from the PM800 as well

Mark

 

[ozflea]

McBob's new toy the PM1000.

Never a wasted day so i rekindled my PM1000 giving the old gal a bit more oomf along the way

Hs a two piece head again made by one of my American friends and fitted with a Tilly HL 293 and a few mods internally

Notice the Dual port muffler ??

Boredom is a pain ................. McBob.

 

[heimannm]

Very interesting project Bob, looks though as if you need more sugar...

Mark

 

[Steve NW WI]

Still on south Pacific time, Mark?

Welcome to the night shift world, if only for a couple days!

 

[promac850]

Kyle maybe your point gap (and therefore timing) is off.


If you're unsure what bar plates you need, post a pic of your bar tail.

I set it at .020"

It is supposed to be set while the arm is on the cam, right? Or is it supposed to be on the low spot on the cam?

 

[a. palmer jr.]

I set it at .020"

It is supposed to be set while the arm is on the cam, right? Or is it supposed to be on the low spot on the cam?

High spot.

 

[watsonr]

It's supposed to be set when the arm is on top of the cams highest point. Try .018... and make sure the air gap is .012.

 

[promac850]

It's supposed to be set when the arm is on top of the cams highest point. Try .018... and make sure the air gap is .012.

Okay, .018" for the points, and then .012 for the coil air gap... I will give that a shot.

Also going to try the flat back carb again. If it popped with that carb, and the primer works, then it should run with that carb.

Now that I think about it, I wonder if I confused the .200" feeler gauge for the .020"... that would be a problem.

Guess I'm off to check the ignition...

 

[Steve NW WI]

Not much chance of confusing .200 for .020, the thickest feeler guage in a normal set is .035. Could be the opposite way though, .002 feeler is a flimsy little thing, feels like paper (most paper is actually a little thicker than .002) .020 feels pretty stout and is roughly the thickness of a fingernail.

EDIT: Regardless of carb function, if everything else is right, it should give a good sputter at least with a small shot of mix down the carb throat.