Mcculloch sp125/101b kart saw build thread

[qurotro]

I tuned mine to around 9500.. Hmmmm

 

[Al Smith]

Since it's been mentioned I'm curious of the actual torque curve of a reed valve Mac .At around 9-10,000 it could be about right .I have no idea what that would be because I tune by ear .On a kart application on a circle track they wanted max RPM's to be right before they hit the turn .On a road course with a zillion turns they wanted the mid range to come on strong .So they ported and tuned accordingly .

 

[Woodslasher]

My buddy got a 101 engine off of ebay and is going to pull the crank out of his extra SP125 carcass to use in it, would he need to weld weights on for it to work in a 101? Can he use the 101 rod/bearings on the 125 crank? Basically, what all can he use from the 125 to make the 101 a saw chassis and what all will he need to source? Outside of the engine parts he has a steel bore SP125 sans clutch cover, filter cover, and recoil assy to pillage for parts.

 

[Bigmac]

If it’s a bolt on sp125 crank,it is interchangeable, I would not weld it. I used to wonder myself, but the bolt on weights are tungsten. You want to run the kart rod and piston, checking clearance is huge on these! If you look back to the beginning of the thread you can see the block mods needed. The kart head needs modded to fit behind the sp fan shroud, and a rear Av mount fabricated, or mod the kart shroud for an Av mount. Lots of info in this thread. If you have any questions feel free to ask!

 

[Bigmac]

I tuned mine to around 9500.. Hmmmm

That’s a good rpm for a stocker

 

[Bigmac]

Anything over 12.5 in the cut is just showing off anyway...

That’s true, but for the uninitiated…. I don’t want to see unnecessary carnage either! Kartsaw action takes some experience, and one flaw and it will eat your lunch! Or luck is on your side! Parts
Are getting rarer and expensive

 

[Woodslasher]

If it’s a bolt on sp125 crank,it is interchangeable, I would not weld it. I used to wonder myself, but the bolt on weights are tungsten. You want to run the kart rod and piston, checking clearance is huge on these! If you look back to the beginning of the thread you can see the block mods needed. The kart head needs modded to fit behind the sp fan shroud, and a rear Av mount fabricated, or mod the kart shroud for an Av mount. Lots of info in this thread. If you have any questions feel free to ask!

My buddy can/may be doing the work on the saw, he typically has me do Mac stuff as I'm "the McCulloch guy" but I'll try to convince him to join up here so's he can bug you guys when he's turning it into a race saw.

 

[Bigmac]

My buddy can/may be doing the work on the saw, he typically has me do Mac stuff as I'm "the McCulloch guy" but I'll try to convince him to join up here so's he can bug you guys when he's turning it into a race saw.

The more kart/mac guys the better! A race saw is another matter… lots of details

 

[Woodslasher]

The more kart/mac guys the better! A race saw is another matter… lots of details

He'll do the race saw stuff, I'm just getting him set up with a saw-type clutch/crank/chassis setup and he'll do the rest. He's converted a Husky 181 into a reed valve saw and runs an HL carby on it so I have faith in his ability to build the 101 into a smokin' hot saw.

 

[Squareground3691]

My buddy got a 101 engine off of ebay and is going to pull the crank out of his extra SP125 carcass to use in it, would he need to weld weights on for it to work in a 101? Can he use the 101 rod/bearings on the 125 crank? Basically, what all can he use from the 125 to make the 101 a saw chassis and what all will he need to source? Outside of the engine parts he has a steel bore SP125 sans clutch cover, filter cover, and recoil assy to pillage for parts.

Saw that 101 on the Bay just recently.

 

[jacob j.]

He'll do the race saw stuff, I'm just getting him set up with a saw-type clutch/crank/chassis setup and he'll do the rest. He's converted a Husky 181 into a reed valve saw and runs an HL carby on it so I have faith in his ability to build the 101 into a smokin' hot saw.

If he's going to do an all-out race saw, I would recommend having him get in touch with Terry Ives and get a heavy-duty connecting rod.

 

[Woodslasher]

Yessir, will do.

 

[Woodslasher]

I'm a bit confused, does the 125 crank need weights period or is it fine unweighted? Does it have weights from the factory? I know I should just look at stuff but I'm busier than chit and I know my buddy will want to go asap when the motor shows up so I want to be as ready as I can.

 

[jacob j.]

The 125 crank had the weights from the factory. As Nathan mentioned, they're bolt-on Tungsten pieces and they're designed for the saw chassis, not the kart chassis. The 101 motors retained the welded
cranks long after the 125 came out. If your buddy wants a motor that turns higher RPM, he's better off finding a good 101 crank.

I'm not sure how a 125 would run without the crank weights - I think it would vibrate quite badly. The 105 uses a similar crank (same stroke) without weights but it has a much smaller and lighter piston.

 

[Woodslasher]

Well, my buddy dropped by Terry Ives' and got his help on this project as well as a n.o.s. saw-type crank for the n.o.s. 101 motor he's using. So..... yeah. I think he'll be alright.

 

[Woodslasher]

Well, my buddy dropped by Terry Ives' and got his help on this project as well as a n.o.s. saw-type crank for the n.o.s. 101 motor he's using. So..... yeah. I think he'll be alright.

I love it when I'm right.

 

[Squareground3691]

I love it when I'm right.
View attachment 358135 View attachment 358136

Nice one !

 

[jacob j.]

I love it when I'm right.
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So are you running a 125 crank without the weights?

 

[Bigmac]

I love it when I'm right.
View attachment 358135 View attachment 358136

Looks great! Can I get a pic of the muffler outlet? Just curious! Did he block off the decomp? Did he get it running?

 

[Woodslasher]

So are you running a 125 crank without the weights?

That's my buddy's saw, he's running the n.o.s. 101 saw-type crank Terry gave him.

Looks great! Can I get a pic of the muffler outlet? Just curious! Did he block off the decomp? Did he get it running?

I'll see if he'll send an exhaust pic, I seem to recall him saying he retained the decomp and I think it's a runner. I gave him a missing grommet and wrap bracket a few days ago and it was pretty much done then.