McCulloch CP 125 build

[Chainsaw Jim]

Put a SP125 intake on it as they have the two reed pedal set up
like what was used in many older saws like 795, 797, etc. The
CP is the only saw I know of that tried that stupid big single reed.

Yeah, I noticed that, but availability is still just as limited. If the only one available goes through the roof on bidding then I'll have no choice but to improvise.
Have you experimented with thicker or thinner petals to check any differences in performance with these yellow beasts?

 

[smokey7]

Have you looked for a blank sheet of reed petal material? It may be way easier to cut your own... A builder i worked as a apprentice showed me to seal the edges with resin after they were cut on fiberglass reeds to prevent fraying.

 

[Al Smith]

That reed looks pretty thick .

 

[Lee H]

Jim I only use the stock reeds. The only CP I restored had a good reed like yours
so I was able to reuse it. The SP intake with reeds shouldn't be to tough to find
since the SP was in production for a much longer time frame. If I had a spare i'd
send it to you but I don't think I do. I'll take a look tomorrow if I get so time.

 

[Chainsaw Jim]

That reed looks pretty thick .

Yes it's .033" thick.

 

[Al Smith]

1 mm is around 39 thou which carbon fiber sheet comes in .I have no idea how a person would figure the degree of flexibilty between carbon and fiber glass but that could be a factor .
As a side note I remember having something apart that had a reed like that but it wasn't a McCulloch .Can't remember what it was ,boat motor maybe ????

 

[RocketRoss57]

Alot of motorcycle shops will carry replacement reeds. You might be able to find one that is big enough to trim down to work for you.

 

[Chainsaw Jim]

Alot of motorcycle shops will carry replacement reeds. You might be able to find one that is big enough to trim down to work for you.

CR500 reeds are large enough to trim down to shape, but they're .048" thick.

 

[Chainsaw Jim]

1 mm is around 39 thou which carbon fiber sheet comes in .I have no idea how a person would figure the degree of flexibilty between carbon and fiber glass but that could be a factor .
As a side note I remember having something apart that had a reed like that but it wasn't a McCulloch .Can't remember what it was ,boat motor maybe ????

Polini makes reed valve sheets up to .018" thick and they come in packs of two sheets. I'm wondering about using the .015" thick ones and just double stacking to beef it up a little.

 

[Al Smith]

There is a lot of help if you Google reeds .They talk about stiffness regarding reed flutter and just about any thing you ever wanted to know about reeds and how to make them .They get into shapes,double racing reeds and other things Just keep in mind this old classic Mac is a worker not a racing snow mobile or a hopped up dirt bike .As long as it runs half way decent that's all it needs .

 

[Lee H]

Reeds can be a very critical part of any reed valve 2 stroke motor.
To stiff and they will open late and close early resulting in less of
a charge in the crankcase. To soft and they will open early and close
later resulting in more of a charge but you get the possibility of carb
spit back and less charge in the combustion chamber.
If your going to make a reed I would stay with the same thickness
and type of material to try to stay in the same parameters that Mac
designed.
If it were me and looking for the most I would call a couple tech supports,
one at Boyseen and the other Moto Tasinari which is V forse reeds and
get a little education as to what will and will not work for this application.

 

[Red97]

I tried some carbon fiber reeds one time...

Don't think they worked too well.

Should be able to find some fiberglass circuitboard sheets that thickness. As an alternative.

 

[Al Smith]

To me the neatest reed set up on a stock chainsaw is on a 2100 Homelite .It has a six petal metal reed assembley set up in pyramid style .A lot of fast acting reed area combined with a relatively large carb .It allows it to take a big old gulp of fuel .In addition the individual reed petals are split having a larger section on one side .I presume this design responds differently under varied RPMS but don't know for sure .--now you talk about something pricey,check out what parts bring for that model .
That saw must have been expensive at the time because the popularity is considerably lower than a Mac 797,125 or Stihl 090 .You just don't find many .I've seen two in addition to the one I own .

 

[jacob j.]

A lot of the karters rob the Homelite 6-petal reed cages to run in aftermarket intakes on the Mac and West Bend kart motors. They make good running machines.

Ken Dunn once built a 2100 Super that had dual-carbs on a Christensen manifold grafted over from a 101B kart motor- that was a pretty wild saw.

 

[Al Smith]

I ran a Ken Dunn 090 once with a 10 pin .It would scoot .

 

[Chainsaw Jim]

I ran a Ken Dunn 090 once with a 10 pin .It would scoot .

Any pics or videos?

 

[TJ the Chainsaw Mechanic]

Is it running yet? lol

 

[Chainsaw Jim]

The new rod bearings went in nicely. Remember to count pins before you start dropping them in place so you know you have them all. In this case I had an extra which took a minute to figure out. The more you have to fool around, the more you risk losing a pin.


Points are set and cover in place...



I'm still waiting for a few parts to arrive.

 

[heimannm]

A dab of grease on the rod and cap will hold those pesky rollers in place while you're putting them together.

Mark

 

[Chainsaw Jim]

A dab of grease on the rod and cap will hold those pesky rollers in place while you're putting them together.

Mark

Good tip Mark.
I rolled em across a few drops of two stroke oil before I stuck em to the race with tweezers. I'm also careful to never use anything magnetic to pick them up to avoid magnetizing the pins. I'd like to think it's better if they don't have any attractive properties to hard metals.