Mcculloch sp125/101b kart saw build thread

[sawfun]

Thanks, my machinest Is a good guy! I think version 2 on the manifold will be a little improvement over the prototype, but I am hoping the adapter is a winner! Getting excited to do some testing! Hoping it’s a good improvemen. The wb37 might be a decent compromise for the bdc, the bdc looks like about a 27mm venture and the wb37 is designed for a 150-200cc engine and has a 25 or 25.5 venture, I am going to test a smaller 24mm venture and see how it goes, will probably get a wb37 for testing too, there is a China knock off of the 37 now too so beware.

I've got a real WB new in box so no China worries for me. You are quite correct on the BDC venturi size. When my buddy saw it he stated, "that looks like the same size throat carb as the one on my Rambler".

 

[Bigmac]

I've got a real WB new in box so no China worries for me. You are quite correct on the BDC venturi size. When my buddy saw it he stated, "that looks like the same size throat carb as the one on my Rambler".

That’s about the truth! The bdc is pretty huge! I don’t think McCulloch intended for it it idle in saw use, probably like when ford debuted the twin 4500 Holley carb on the 302 mustangs in 68 the for road racing. It was the era! Big carbs and going fast!

 

[sawfun]

That’s about the truth! The bdc is pretty huge! I don’t think McCulloch intended for it it idle in saw use, probably like when ford debuted the twin 4500 Holley carb on the 302 mustangs in 68 the for road racing. It was the era! Big carbs and going fast!

The giant intake ports & valves of the 351 Cleveland 4bbl were way in excess for its size, especially on the street, as well.

 

[Al Smith]

A Cleveland 351 was a hydrid contraption ,part small block with huge valves and a lot of carb .My brother had a Boss 351 C in a Mustang .It would scoot .The big blocks like 429 were built at the plant I retired from .My name is on one or two of the very last engines ever made .It was a large truck engine by that time .Big heavy thing,all iron with a steel crankshaft ,hard insert valve seats .Made to run forever .

 

[sawfun]

A Cleveland 351 was a hydrid contraption ,part small block with huge valves and a lot of carb .My brother had a Boss 351 C in a Mustang .It would scoot .The big blocks like 429 were built at the plant I retired from .My name is on one or two of the very last engines ever made .It was a large truck engine by that time .Big heavy thing,all iron with a steel crankshaft ,hard insert valve seats .Made to run forever .

My buddy had a 351 Cleveland 4bbl that came in his Pantera. The sound with headers and the engine right behind your head was very unique.

 

[Bigmac]

Got the manifold back and it’s correct now! And there’s two of them...



and it matches the reeds nicely And the boot is a perfect fit!!

 

[sawfun]

Got the manifold back and it’s correct now! And there’s two of them...

View attachment 210895 View attachment 210894

and it matches the reeds nicely View attachment 210896And the boot is a perfect fit!!View attachment 210893

That looks fantastic!!!

 

[Bigmac]

Did some mock up on the cp block
May have to relieve the top of the adapter a little for extra clearance, the carb mount and the angle of the 45° bevel aren’t exactly what I would like. I have a great fit to the carb and airbox floor, and my custom manifold is on the right angle to match the floor but the bevel in the tank isn’t ideal. Going to have to do more fitment work and see if any adjustments will be needed. I might adjust a gasket thickness to make it as good as possible, the next manifold will be a lot easier!!

 

[Bigmac]

Got the tank mounted to the a mock-up kart block and oil tank, liking the fit and function of everythingeverything on the intake track is connected and the antivibe is still functioning properly

 

[Bigmac]

Got it running! Would like to be able to get it a little richer in the h screw, but it’s 2 turns out, and going to 2.5 dose not do much

 

[jacob j.]

That sounds real healthy Mr. N - that should be a winner with a 50" bar and chain.

 

[sawfun]

As JJ said, that saw sounds like it's ready for long bar work. Now I'm guessing 1/2" chisel or .404 with the rakers way down.

 

[Bigmac]

I’m excited to get it into some wood, but I am a little concerned about the H tune, would like it to be richer,I would like it to be able to four stroke to limit the rpms, it may be fine thou. May have to make some adjustments to the carburetor

 

[Lee H]

Sounds pretty healthy. Doe's the carb have a hi jet inside. if so it may need to
be changed to a larger size or drilled.

 

[Bigmac]

I’m going to take it apart tomorrow and check the jet and metering lever, probably check the pop off pressure too

 

[Bigmac]

OK, took the carB apart, it does not have a traditional main jet. Did a bunch of reading and research, checked the meter and lever height it’s dead on pop off Was a little lower than spec, supposed to be 18 pounds and this is 13-14 but the resting position is correct at 10 not sure if a spring change would make much difference or not, apparently a lot of kart guys drop the pop off pressure down to 8-10. The other thing in researching this carburetor, was that on the Kt100 is that it is difficult to get them to idle without loading up and run properly in the mid range, cart specs for the KT 100 1 and three-quarter to two turns out on the low speed and an 1/8th to a quarter turn out on the high-speed if I adjust it to two turns out on the low and two turns out on the high at four strokes hard now and returns to idle quickly like I would like, but will also Load up at idle just like the kart guys complain about. It takes a while like 20-30 seconds On the cart forums they were saying to start it up with one turn out on the low speed once you got it warmed up and running they would turn it out to one and three-quarter to two turns for racing and then once done racing turn it back to one turn to idle.

It also seems to be sensitive to tank venting, it acts like it’s not getting enough fuel unless I have the cap loose, I swapped a couple caps from other saws that worked fine, and it still sensitive, I think it’s sucking quite a bit of fuel, have run through over two tank of gas just messing around!!

 

[jacob j.]

You might have to pull the duckbill out of your fuel cap (if you have one) and just run some type of "chore girl" element in the cap to keep fuel from leaking.

 

[Bigmac]

You might have to pull the duckbill out of your fuel cap (if you have one) and just run some type of "chore girl" element in the cap to keep fuel from leaking.

I pulled the duckbill out and cleaned the mesh screen in the cap it flows pretty now, and it dose help. Pulled the baffle out of the muffler to see if that would make any difference as well, not super noticeable, it did want to idle a touch higher with the baffle out, And I can get it to idle better a little higher in the RPMs, but I think that’s going to be too fast for the clutch.

 

[sawfun]

I pulled the duckbill out and cleaned the mesh screen in the cap it flows pretty now, and it dose help. Pulled the baffle out of the muffler to see if that would make any difference as well, not super noticeable, it did want to idle a touch higher with the baffle out, And I can get it to idle better a little higher in the RPMs, but I think that’s going to be too fast for the clutch.

Were you running the saw with a long bar and the clutch still pulling through?

 

[Bigmac]

Were you running the saw with a long bar and the clutch still pulling through?

I hadn’t put a barn chain on yet, more of just a sound and feel thing at that point, I just put my 32 inch test bar on, and I can get it to idle just below the clutch engagement but every once in a while it’ll hang just a hair above and spin the chain. I think I’m going to lower the pop off pressure and see if that makes a difference, I have both screws turned 2 turns out it still wanted to run out of fuel on the top, The only other thing it could be is my impulse inlet end of the manifold is a little bit small, not sure if that’s enough to affect it either