McCulloch Super Pro 125c build thread

[jacob j.]

Old vs. New - iron-liner 125 vs. 125c.

 

[Frank bierce]

Old vs. New - iron-liner 125 vs. 125c.

Very nice!!!

 

[jacob j.]

Very nice!!!

Yeah, the Chrome-bore motor definitely turns up higher. One factor could also be that the chrome-bores can run a much tighter-tolerance piston.

 

[Lee H]

Not sure which one is the C but the second saw is getting it done.
Very noticeable difference. What carbs are on both and are both
recently rebuilt

 

[jacob j.]

Not sure which one is the C but the second saw is getting it done.
Very noticeable difference. What carbs are on both and are both
recently rebuilt

Lee - The second one is the 125C, both have the Walbro SDC-20 carbs, both are fully rebuilt with similar run time. Both got brand new
pistons and rings, bearings, seals - the works. Both have stock porting/manifolds and are running 7-tooth sprockets (3/8ths).

McBob was the one that told me the "C" motors could be turned up higher. I know one main difference here is that the piston to cylinder
wall clearance in the C motor is about .0031", whereas the iron-liner motor is the standard .0055".

 

[Lee H]

I could be wrong on this but i bet if the iron liner saw had a few tanks run through it to break it in it would
most likely perform much better. The chrome bore saws tend to break in much sooner with little run time.

 

[jacob j.]

I could be wrong on this but i bet if the iron liner saw had a few tanks run through it to break it in it would
most likely perform much better. The chrome bore saws tend to break in much sooner with little run time.

I'm hoping so, Lee. The chrome-bore saw was a runner right out of the gate - it may just have particular port timing numbers in it that is a good recipe. It's an
early chrome cylinder. I took both of these saws to the PNW GTG last year and everybody was raving about this "C" motor, and the one ported iron-liner
saw I had there (.030" over). Of course, Nathan's saws were much stronger - one had the WB carb and the other was a kart motor.

 

[NPKenny]

@jacob j.

A few pages back, you referenced running a Tillotson HS- 296 from an 390xp as a potential carb on one of these saws. Did you ever make that happen?

I’m looking for an H and L adjustable carb for a Super Pro 105. SDC-20’s are difficult to find and I am leery of fitting a smaller SDC from a 10-series, although that is my current best option

 

[jacob j.]

@jacob j.

A few pages back, you referenced running a Tillotson HS- 296 from an 390xp as a potential carb on one of these saws. Did you ever make that happen?

I’m looking for an H and L adjustable carb for a Super Pro 105. SDC-20’s are difficult to find and I am leery of fitting a smaller SDC from a 10-series, although that is my current best option

I haven't been able to make that happen yet. Life got in the way.

I think another good candidate would be the HS-136 off of a Husky 2100. I think on that one though you have to plug the governor.

 

[fossil]

@jacob j.

A few pages back, you referenced running a Tillotson HS- 296 from an 390xp as a potential carb on one of these saws. Did you ever make that happen?

I’m looking for an H and L adjustable carb for a Super Pro 105. SDC-20’s are difficult to find and I am leery of fitting a smaller SDC from a 10-series, although that is my current best option

Look for an SDC-37 or 38. Same venturi as the SDC-20

 

[jacob j.]

Look for an SDC-37 or 38. Same venturi as the SDC-20

A couple changes would need to be made if wanting to use a 37 or 38

1. - Convert to external impulse

2.- A small amount of material may need to be ground away from the manual oiler button boss to clear the adjustment screws (not on all 105/125s, it depends on which tank they have)

3. - Throttle shaft may need to be changed to be compatible with the 105/125 throttle rod, or a new throttle rod may need to be made.

 

[fossil]

A couple changes would need to be made if wanting to use a 37 or 38

1. - Convert to external impulse

2.- A small amount of material may need to be ground away from the manual oiler button boss to clear the adjustment screws (not on all 105/125s, it depends on which tank they have)

3. - Throttle shaft may need to be changed to be compatible with the 105/125 throttle rod, or a new throttle rod may need to be made.

I wonder if some of you guys may have investigated the the main jet hole diameter on some of the SDC carbs. I've never had the ambition nor do I have any gauge pins to pull the screen and flap disc in the check valve well.
Might be worth a look if there are any unused carbs the shelf.

I think all the SDC's that MAC used were a fixed main jet.

 

[NPKenny]

I think all the SDC's that MAC used were a fixed main jet.

Please explain this. I'm not sure I am tracking. The SDC's all have H and L screws in the McCulloch saws I have.

I think it would be helpful to understand if one of the 10-series SDC's (with listed modifications) would properly fuel a 125 or 105, even with the same venturi size.

Or would a Walbro WJ-115 from a 395XP work better?

Or would a Tillotson HS-296 from a 390XP work better?

 

[jacob j.]

I think those would be higher performing carbs regardless, as long as you could sort the throttle and choke rods. Bellhopper put an RWJ-4 (372-XT) carb on one of his
125s and it ran quite good from what I could see in the video.

 

[NPKenny]

Here is a Walbro SDC-37a from a 10-10A mocked up in a Super Pro 105. The manual oiler boss will require clearancing. The throttle rod is easily fit with a drilled hole. The choke should be very straightforward. The impulse nipple would be simple.

I’m not familiar with how grinding the oiler boss in the tank will impact the manual oiler.




The 372 carb I have to reference is a Walbro HD which is absolutely not a fit. The carb must have mounting holes angled across the Venturi to fit well in the carb box.

SDC-65 from a Pro Mac 10-10 with angled needles requires significant clearancing compared to the SDC -37.

 

[Bigmac]

Here is a Walbro SDC-37a from a 10-10A mocked up in a Super Pro 105. The manual oiler boss will require clearancing. The throttle rod is easily fit with a drilled hole. The choke should be very straightforward. The impulse nipple would be simple.

I’m not familiar with how grinding the oiler boss in the tank will impact the manual oiler.


View attachment 342686

The 372 carb I have to reference is a Walbro HD which is absolutely not a fit. The carb must have mounting holes angled across the Venturi to fit well in the carb box.

SDC-65 from a Pro Mac 10-10 with angled needles requires significant clearancing compared to the SDC -37.

If you grind the tank you may have to shorten the manual oiler, their is at least two styles of manual oiler button. Here is the sdc20 for reference

 

[heimannm]

This is the data I have accumulated for the SDC carburetor models. Note that all of the models 18 up have the larger venturi and throttle bore.

McCulloch Carburetor Usage – SDC & Zama C2 Carburetors

Carburetor Venturi Throttle Idle Hi Used On

SDC 2 .625 .750 Ext Adj 1-10, 2-10A, 2-10PS, 2-10G, S2-10, 3-10E, 5-10E, 5-10G, 6-10, LG 6A, S LG2, S6-10A, S10-10, S10-10A

SDC3 .625 .750 Int Adj 10-10, 10-10A, 10-10E

SDC4 .625 .750 Int Adj 10-10

SDC7 .625 .750 Int Adj Mac 15 (no FP)

SDC16 .625 .750 Ext Adj S10-10, S10-10A, S10-10E

SDC18 .750 .812 Ext Adj CP55, CP70, CP70L, 7-10A S2-10A, S6-10A

SDC19 .750 .812 Int Adj 795L, S797

SDC20 .750 .812 Int Adj CP125

SDC22 .750 .812 Ext Adj S2-10, 7-10A

SDC37 .750 .812 Int Adj 10-10, 10-10A

SDC38 .750 .812 Ext Adj SP80

SDC38A .750 .812 Ext Adj SP55, 60, 70, 80, 81, 81E, PM570, PM850

SDC43 .750 .812 Int Fixed MC49E

SDC44 .750 .812 Ext Adj 7-10A, PM60

SDC49 .750 .812 Int Fixed PM55, PM60, PM555, PM700, PM10-10S

SDC50 .750 .812 Int Fixed SP60

SDC51 .750 .812 Ext Fixed SP81

SDC65 .750 .812 Int Adj PM10-10, Pro 10-10A


Zama C2 .750 .812 Ext Adj PM850, 800, 805

Edit - sorry but the formatting was lost in the copy/paste, I think you can get the gist of it.

Mark

 

[heimannm]

Here it is in a .PDF

Mark

 

[Lee H]

Nice info Mark

 

[heimannm]

I have an SP125 that came to me with one of the smaller SDC carburetors, I will have to check the number tomorrow. I swapped an SDC 20 from a CP70 in place of it after adding the external impulse fitting and there was a noticeable improvement in performance. The throttle linkage turned out to be perfect in terms of the idle position since I had no idle speed adjustment provision with the change in carburetors.





Getting to the H adjuster is a bit of a trick.



Mark