Mcculloch sp125/101b kart saw build thread

[Lee H]

Bigmac, I hope you don't mind me asking questions in your thread instead of starting a new one. I have been looking through your thread and have read a lot. May I ask you guys with experience here how well does the 101 run on an original saw carb such as an SDC20? Does it act starved? Is it a must to make a manifold and put a bigger carb on the 101 saws? Whats the difference between each 101 variation? I apologize for so many questions, but really interested in these saws.

Scott, To answer your question, Yes. The 101 motors were designed to run with open header and
came with the Mac BDC carb with a 1 3/8 throttle bore. Running a 101 in a stock saw chassis is
detuning it quite a bit. They still run well but not like they were designed. I have both. A stock 101
in a stock chassis and a custom saw with a 101 with open header and a Tilly HR carb. That saw is an
animal and a blast to run.

 

[Scott Kelsey]

Thanks for the info guys. I just purchased a 101 and was thinking of building a 101 saw, but not sure at this point.

 

[jacob j.]

Thanks for the info guys. I just purchased a 101 and was thinking of building a 101 saw, but not sure at this point.

It's a lot of work - depending on what you want to end up with. The saws that Nathan and Lee have posted have many hours of labor into them. I'm working on two right now
for members here and I'll probably end up with 30 hours labor into each with cleaning, assembling, getting parts modified/welded, tuning, testing in the wood, etc. I have SP
saws that I probably have 25 hours labor in with porting, replacing freeze plugs, going through different carburetors, sand blasting parts, etc.

The plus side is they're a lot of fun and very satisfying once you have them running right. There's tons of literature out there on these motors and we've posted some in this
thread and the main McCulloch thread.

 

[Bigmac]

Thanks for the info guys. I just purchased a 101 and was thinking of building a 101 saw, but not sure at this point.

What are your reservations? They are fun and rewarding to build! What are you hoping for? We can help you get what you want I’m sure! Half the fun is finding the parts, and dreaming the builds!

 

[Scott Kelsey]

Bigmac, simply trying to decide if I want to put the 101 into a saw, shelf the 101, send it down the road or restore the saw to stock. Asking questions and reading everyone's old threads/comments to weigh the work of a 101 vs. Stock and the desired result.

 

[Lee H]

Bigmac, simply trying to decide if I want to put the 101 into a saw, shelf the 101, send it down the road or restore the saw to stock. Asking questions and reading everyone's old threads/comments to weigh the work of a 101 vs. Stock and the desired result.

One question Scott, Have you ever run a saw with a 101 in it? The biggest thing is deciding which
route to go and what your capabilities are. The easiest to build is a stock appearing saw using the
stock carb. The only issue on this type of build is the rear AV mount where it mounts to the head.
Otherwise all the 125 stuff will bolt onto it.

 

[Scott Kelsey]

Lee, I have never run a saw with a 101 in it. I have run 797's and a stock SP125, but that is the extent of my experience. I do know i have the fabrication experience to build a modified 125, but the knowledge,, no. May keep the saw stock. Time will tell. I appreciate your words and help as well as everyone's else's here. It definitely a decision to make.

 

[Lee H]

There is a huge difference between a 101 saw and a stock 797 or 125. If you already have the 101
motor i say go for it. You have nothing to lose and have all the help you will need right here in
this thread.

 

[Bigmac]

Bigmac, simply trying to decide if I want to put the 101 into a saw, shelf the 101, send it down the road or restore the saw to stock. Asking questions and reading everyone's old threads/comments to weigh the work of a 101 vs. Stock and the desired result.

I get it, it’s a bit of an unknown for you. I have been collecting parts for almost 10 years from these, trying to find deals when I can. If you have a chrome cylinder that needs replated then a 101 swap is a good plan imho! Basically anybody that can build a stock sp125 can easily do a stock carb 101, super easy swap. As the guys have said the rear Av mount is the only issue, and drilling the manual oiler hole in the block. It’s a fun build, and is authentic to the era. I wouldn’t recommend the big carb/reed swap for a first project, unless you have some help. Have some knowledge to how these are supposed to run and common issues is helpful, lots of help here! If your nervous about anything, let one of use know, and I am sure we can help. If you want help moding the head or shroud, shoot me a pm.
I might make a small run of the intake manifolds and adapters, have has several people ask for them, but it’s not a mod for everyone for sure!

 

[Lee H]

I'd be interested in an intake and adaptor if that is what you used on the CP build.

 

[jacob j.]

I might make a small run of the intake manifolds and adapters, have has several people ask for them, but it’s not a mod for everyone for sure!

I'd be interested in an intake and adaptor if that is what you used on the CP build.

I would too.

 

[Bigmac]

I'd be interested in an intake and adaptor if that is what you used on the CP build.

I would too.

Ok guys, it’s not going to be fast, I want to make a few more for my self and have had a several other requests. I can probably make a gas tank template that can get you close, and maybe a line graph jig to bend the throttle rod. The next batch was going to get a thicker base plate. It’s definitely hand made, lol, and I used motoseal to make sure everything sealed up. Still kinda reluctant because it’s a tight fit, a 1/16 hear or there and the fitment can be off.

 

[Bigmac]

Talked to my welder machinist friend, and he is game for a run of manifolds and adapters! Can have the surfaces machines but it would cost extra. I can make them for a saw or kart shroud, it makes it more material, a saw version that can be cut down is probably the smart thing.

 

[Bigmac]

I would love to find a good source for impulse 90°

I can get the smaller ones fine, and they work fine, would just be nice

the only way I can find the large walbro of the wb is to get a complete top cover, they aren’t crazy expensive, but it adds up

 

[Lee H]

Have you tried Mcmaster Carr or any of the racing kart places. Just a thought.

 

[Scott Kelsey]

Well, here is the 101 I purchased. Needs a good cleaning. Numbers on the bottom are 66019. Did some exploring and it has a .040 over piston. In one of the pictures you can see ports with grooves that run into them. Hoping that it can be bored out and a piston can be found. Feel free to tell me what you think.

 

[Scott Kelsey]

 

[Bigmac]

Definitely a mc101

 

[Lee H]

Early 101 with the bridged exhaust port and the aluminum head gasket.
Still a nice motor. Terry Ives has pistons up to .068 over in .004 increments.

 

[Bigmac]

Well, here is the 101 I purchased. Needs a good cleaning. Numbers on the bottom are 66019. Did some exploring and it has a .040 over piston. In one of the pictures you can see ports with grooves that run into them. Hoping that it can be bored out and a piston can be found. Feel free to tell me what you think.

Nice block, yes easily bored out. Looks like it was needed at some point. That head chamber is different than I have seen before. I have a couple questions for you. Dose the piston sit flush with the top of the block at tdc? And could you measure the distance from the top of the. Cylinder to the top of the exhaust port? Or have access to a timing wheel?