McCulloch Super Pro 125c build thread

[jacob j.]

Hey Lee -

Yeah, that was a service part for the early shrouds when the mounting tabs would break off or the captured nut would work its way out. McBob posted the service bulletin
on it once but it got lost in the great Arboristsite hack years ago.

 

[jacob j.]

Well, the latest .030" over saw with the pop-up piston is a runner:

 

[Bigmac]

Sounds good! How dose the compression feel?

 

[Bigmac]

It can’t be worse than me thinking 230 pounds is 165psi! Lol

 

[jacob j.]

Sounds good! How dose the compression feel?

This one is pretty good, but not as good as the .010" over saw, because the piston in this saw just isn't as tight a fit in the bore. It was a used piston
to begin with and as you know, these Mac engines tend to wear in a more oval pattern than most other saw engines. This piston had some wear on
the skirt facing the rear transfers. It's got good pop though, probably around 175-180 and will likely gain another 5-8 psi as I get more time on it.
This one I'll try some other ideas on - maybe a more aggressive stuffer like what my dad used to run and a better carb.

 

[jacob j.]

The final result between Kream and Redkote on these Mac tanks - I think overall I like Redkote better. It's harder to work with up front, but stays more
flexible and is easier to clean up. Kream hardens pretty good, and can be cleaned up with aerosol Brake cleaner, but it takes some elbow grease. The
Redkote can be trimmed and physically removed even after curing. The Kream probably penetrates cracks better though. Two different products and
they're both good. Kream can be thinned out with M.E.K. and I think Redkote can be thinned out with lacquer thinner.

 

[Bigmac]

This one is pretty good, but not as good as the .010" over saw, because the piston in this saw just isn't as tight a fit in the bore. It was a used piston
to begin with and as you know, these Mac engines tend to wear in a more oval pattern than most other saw engines. This piston had some wear on
the skirt facing the rear transfers. It's got good pop though, probably around 175-180 and will likely gain another 5-8 psi as I get more time on it.
This one I'll try some other ideas on - maybe a more aggressive stuffer like what my dad used to run and a better carb.

Awesome! I was way off! Lol

ya I still haven’t got my stuffer swapped, it’s clearanced and ready to go, but time! Lol after see Joes dyno info, I think the stuffer could be a big key, am excited to test!

 

[jacob j.]

Awesome! I was way off! Lol

ya I still haven’t got my stuffer swapped, it’s clearanced and ready to go, but time! Lol after see Joes dyno info, I think the stuffer could be a big key, am excited to test!

I think your modified intake manifold and an aggressive stuffer together would make a great runner on any of these engines. In fact, it might be a good test on a "C" motor since
McBob said those could be turned up a lot higher than the iron-liner bores. I'll set-up an intake manifold similar to yours and pair it with an aggressive stuffer.

 

[Bigmac]

I think your modified intake manifold and an aggressive stuffer together would make a great runner on any of these engines. In fact, it might be a good test on a "C" motor since
McBob said those could be turned up a lot higher than the iron-liner bores. I'll set-up an intake manifold similar to yours and pair it with an aggressive stuffer.

It’s going to be interesting to test! I am pretty excited to test the stuffer, especially after seeing the dyno info

 

[Red97]

Well, the latest .030" over saw with the pop-up piston is a runner:

Don't you hav any ugly ones?

Them pretty ones are scary

 

[jacob j.]

Here's some McCullah piston and cylinder info for you boys:

 

[Lee H]

Nice info Jacob, I have the mac ipl on saws and kart motors piston and cylinders. What caught my eye on yours
is the first page under non current models i see a 797L, never heard of that. Seen the 795L as i have one and they
were common overseas. So was there ever a 797L in production. I built one not all that long ago just for kicks and
it looks kool with the left hand starter.

 

[Bigmac]

Nice info Jacob, I have the mac ipl on saws and kart motors piston and cylinders. What caught my eye on yours
is the first page under non current models i see a 797L, never heard of that. Seen the 795L as i have one and they
were common overseas. So was there ever a 797L in production. I built one not all that long ago just for kicks and
it looks kool with the left hand starter.

That would be cool to see, I have been thinking about building a 797/101L....I know you have, it’s a cool saw!
I know it’s off topic, but it wonder if the pm105 exists with the 795 top tank and sp105 decomp style cylinder, with the exhaust mount heat sheld.

 

[Lee H]

There are a a few PM105's overseas, I have seen collectors post pic's on chainsaw collectors corner.
Most with half wraps. I have about 4 or 5 pistons for the PM105's. There were advertised wrong and
I bought a few to only find out they were wrong for what I needed them for.

 

[fossil]

I may have asked this question before, but what do you folks set your points gap at for a CP125?

Thanks

 

[Bigmac]

I may have asked this question before, but what do you folks set your points gap at for a CP125?

Thanks

.021, that’s basically the max you can usually get before they are always open, in my experience

 

[Lee H]

.021, that’s basically the max you can usually get before they are always open, in my experience

I agree 100% especially new ones, New points will close a thou or so when run in.

 

[heimannm]

I try for 0.019 -0.020" and check them again once they are cinched down. I am not so often after absolute maximum performance/HP but in search of the most reliability including good starting performance.

Mark

 

[Maintenance Chief]

I think your modified intake manifold and an aggressive stuffer together would make a great runner on any of these engines. In fact, it might be a good test on a "C" motor since
McBob said those could be turned up a lot higher than the iron-liner bores. I'll set-up an intake manifold similar to yours and pair it with an aggressive stuffer.

How come I've never seen a HT style carb on a Big McCulloch? Say off an earlier 088 or 084. The mounting holes are the same spread as a tillotson type carb.

 

[Bigmac]

How come I've never seen a HT style carb on a Big McCulloch? Say off an earlier 088 or 084. The mounting holes are the same spread as a tillotson type carb.

I don’t believe the mounting holes of the ht is a direct swap. It would be a great swap, but the packaging of the carb, tuning screws throttle linkage and impulse port make it a challenge. The wb is tight, but an easier swap, the other challenge is the intake boot being sized for the smaller carb.
Here is the wb37