Mcculloch sp125/101b kart saw build thread

[Bigmac]

Good stuff Jacob! I was reading on a kart forum that the Mac thin ring piston was only good for around 15 hp and the wiesco’s ring was able to get them into the mid 20+ hp level

 

[Lee H]

Guessing the Wiseco ring sealed better with less drag

 

[qurotro]

Man she's loud and poppy.

 

[Lee H]

She looks great, Get her in some big wood and you will love her.

 

[Bigmac]

Got a 101aa short block almost wrapped up. It’s .048 over. The piston is stamped.050 but Terry remarked it to .048 But before I put the head on, I wanted to do some timing tests with the wheel, and check some flywheels for variations The top flywheel is 26° advance, the middle two are 25° and the bottom one is 24°
Kinda interesting
Ps: all standard flywheels

 

[Lee H]

Interesting Nate, Are all the flywheels 101 or 125, 797, I know a lot of other models
like a 250 will work but maybe the timing is different. Could be just manufacturing.

Oh and clean the coil, It's dirty

 

[Bigmac]

Interesting Nate, Are all the flywheels 101 or 125, 797, I know a lot of other models
like a 250 will work but maybe the timing is different. Could be just manufacturing.

Oh and clean the coil, It's dirty

So the yellow was 797, the next one is 101aa and the bottom two are 125. I think it’s just production variation, but could explain why some saw run fine with a chip or not. Have read that they can vary a lot in the kart forums. Some guys have jigs to check them. Might take an old bad crank and make a jig too.

Haha, ya that coil is ugly! I has a bad lead, so just using it as a timing reference. Was thinking of marking it as a fast tool to set timing, I could have a standard and 5° mark and maybe a 7° and 3°
I also am going to reference how much each .010 cut off the key changes the timing

 

[qurotro]

A short clip of her today.

 

[Lee H]

Gotta love a Mac 125, She sounds great.

 

[Bigmac]

A short clip of her today.

Sounds really good! Nice and poppy!

 

[qurotro]

What's the max rpm for it, I haven't ever rev her a lot.
Or should I pull the flywheel to service the points? There's a felt wiper as I know of, oil the lobe?
I'm not planning to put it to work though, just some test cuts once a while to stretch her legs, to admire such a fine piece

 

[Bigmac]

What's the max rpm for it, I haven't ever rev her a lot.
Or should I pull the flywheel to service the points? There's a felt wiper as I know of, oil the lobe?
I'm not planning to put it to work though, just some test cuts once a while to stretch her legs, to admire such a fine piece

I have never put a tac on one, just set them up to clean up in the wood. Don’t hurt to check the points, it doesn’t sound bad though

 

[qurotro]

I have never put a tac on one, just set them up to clean up in the wood. Don’t hurt to check the points, it doesn’t sound bad though

Should I oil the felt wipe for the point lobe?

 

[Lee H]

Don't oil the felt. The oil will get sprayed everywhere. Just a tiny dab of grease on the
points block that rides on the crank.

 

[jacob j.]

Little project action I have going for members here:

 

[Bigmac]

Little project action I have going for members here:

Looks good! I like you av linters! You should do a write up on that!

 

[Lee H]

Mmmmm Yummy, Are your decomps in different locations. I to like the AV limiters

 

[jacob j.]

Looks good! I like you av linters! You should do a write up on that!

Mmmmm Yummy, Are your decomps in different locations. I to like the AV limiters

Thanks guys - yeah they're Stihl 066 case buffers. I don't have any of the regular buffers that came on the 125 cylinders, so I used these and mounted them with lock-nuts and Blue Loctite.

The heads are interesting for sure - I got them years ago from a kart guy that had already modified them and he was hand-starting his motors.

Now that Nathan has discovered the variation in timing on some of the flywheels, I'll have to check mine over real good and look for some that have the better timing.

 

[Bigmac]

I was inspired Jacob, this what I came up with! Lol I am short on limiters too!
stated working on the av mount! Need some more washers.

 

[Bigmac]

Now that Nathan has discovered the variation in timing on some of the flywheels, I'll have to check mine over real good and look for some that have the better timing.

I did the reference for timing, and the key, every .010 is 2.5° so .020 will get you 5° advance! Nice to finally know!