Mcculloch sp125/101b kart saw build thread

[Bigmac]

Drop the pop off pressure to 8 pounds and a five psi hold it helped a tiny amount to be richer but not crazy and it still acts like it wants to run out of fuel if I hold it open for a long period of time

I did do a pressure VAC test when I installed everything, and it passed with flying colors

 

[jacob j.]

What fuel filter are you running?

 

[Bigmac]

What fuel filter are you running?

I had a brand new Husqvarna one, and then I switch back to a new old Mac filter
I did a blow through test and the Husqvarna one was a little more restrictive than the old felt One

 

[Bigmac]

I think I’m going to put the larger impulse Barb on my intake manifold and see if that makes a difference

 

[sawfun]

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

Ok, the reason I asked was after receiving my 090 back from Randy he had told me that the clutch was engaging at idle. Sure enough it was without a bar and chain. In fact you could hardly stop it with a long 2×4 against it. I was hesitant to put a bar and chain on it but took it to a gtg with a 72" bar & chain where I knew I'd have some experienced help. The saw behaved normally, but take the bar and chain off and the clutch runs fully engaged. These high powered big saws seem to need a bar and chain to pull them down. Though I'd have thought my 2×4 pressure was a lot more of a drag than a chain.

 

[Bigmac]

Ok, the reason I asked was after receiving my 090 back from Randy he had told me that the clutch was engaging at idle. Sure enough it was without a bar and chain. In fact you could hardly stop it with a long 2×4 against it. I was hesitant to put a bar and chain on it but took it to a gtg with a 72" bar & chain where I knew I'd have some experienced help. The saw behaved normally, but take the bar and chain off and the clutch runs fully engaged. These high powered big saws seem to need a bar and chain to pull them down. Though I'd have thought my 2×4 pressure was a lot more of a drag than a chain.

Thanks Don, I have experienced that on one of the 125’s the chains would spin on the 36” bar a little bit but not the 50”at all! I think this will be fine with a 50” at idle. It’s getting closer, but still have some bugs to work out!

 

[Bigmac]

Not sure if I’m just gonna have to upgrade the entire fuel system get a bigger fuel line fuel filter and even more free-flowing vent as well, I can’t believe how much fuel I burn through just messing around a little earlier I threw the bar and chain on and cut into a stump, the saw ran hard, but wanted to run out of fuel after about 5 seconds WOT, it also burned over a 1/3 of a tank of fuel!!

 

[sawfun]

Not sure if I’m just gonna have to upgrade the entire fuel system get a bigger fuel line fuel filter and even more free-flowing vent as well, I can’t believe how much fuel I burn through just messing around a little earlier I threw the bar and chain on and cut into a stump, the saw ran hard, but wanted to run out of fuel after about 5 seconds WOT, it also burned over a 1/3 of a tank of fuel!!

Well at least you know your likely making some horsepower. Now as for the EPA, ha ha ha.

 

[Bigmac]

Well at least you know your likely making some horsepower. Now as for the EPA, ha ha ha.

Ya I like how it’s running minus a wot starvation. Haha! Ya the epa, I think I just burned up my carbon credits for a year! Lol

 

[Bigmac]

Been thinking about it for a while. The odd thing with this carb is I can get it to idle and rev once with it set at one turn out on the l an h screw, but if I old it open it screams. With it 2 turns out on both it was better but I had to turn in the butterfly screw to get it to idle, but it ran well like that, could rev it hard three to five times and it then start to over rev. Then I adjusted the pop off to 8psi, it then seemed richer everywhere...but it I reved it up 5 times it sounded rich.. so I held it wot for 5 seconds then it cleared out and over reved. I am thinking it’s more restrictive fuel delivery, or my impulse barb on the manifold. I will try the barb tomorrow. Think I will call terry too, I got the carb from him, he might have some advice

 

[sawfun]

Calling Terry sounds like a proper plan. I had a larger fuel line (1/4") on my BDC saw. I had the saw at an infamous builder and he put it back to the stock one, and did not understand why I did what I did. In racing cars, you always want an much supply as possible on the intake side on the fuel delivery system, be it carb or injection. CR & KX 125's have a larger line than the stock 125's macs do. I haven't got it running, nor tried since I got it back from him some time ago. I kinda expect fuel delivery issues when under a big load. I ran that saw when it was pig rich a few years ago and wouldn't rev over 6000 rpm. The carb needle lever position made almost no difference, however spring pressure did. The carb came with several length springs, I tried the next longer length spring and the saw started and ran like you would have expected. By the way, even pig rich and blubbering, it cut faster than my strong 125c at full rpm. I tried it in a log with a 36" bar buried just to get it in wood.

 

[Bigmac]

Calling Terry sounds like a proper plan. I had a larger fuel line (1/4") on my BDC saw. I had the saw at an infamous builder and he put it back to the stock one, and did not understand why I did what I did. In racing cars, you always want an much supply as possible on the intake side on the fuel delivery system, be it carb or injection. CR & KX 125's have a larger line than the stock 125's macs do. I haven't got it running, nor tried since I got it back from him some time ago. I kinda expect fuel delivery issues when under a big load. I ran that saw when it was pig rich a few years ago and wouldn't rev over 6000 rpm. The carb needle lever position made almost no difference, however spring pressure did. The carb came with several length springs, I tried the next longer length spring and the saw started and ran like you would have expected. By the way, even pig rich and blubbering, it cut faster than my strong 125c at full rpm. I tried it in a log with a 36" bar buried just to get it in wood.

What were you using for a pickup filter for the 1/4 line?

 

[sawfun]

What were you using for a pickup filter for the 1/4 line?

I found a bronze filter at a bike shop that worked well. And the grey Tygon fuel line fit the hole in the tank perfectly sealing itself.

 

[Bigmac]

I found a bronze filter at a bike shop that worked well. And the grey Tygon fuel line fit the hole in the tank perfectly sealing itself.

Was it like this

 

[sawfun]

Was it like thisView attachment 211755

Mine was pretty similar.

 

[Bigmac]

I called Terry, he didn’t feel the fuel line was an issue, he also didn’t think the impulse was an issue but he also said to make sure the impulse is the same size as the carb barb, so I will do that first. He said to drill the high speed next, he was surprised but said it must need more.
So I will redo the impulse setup then drill the carb if needed

he was glad I adjusted the pop off pressure, he said it was too high, but also said it wouldn’t make a huge difference, he confirmed the carb was designed for 1.5 turns out and 1/8 turn on the h, he basically said if your at 2 you need to drill

 

[Bigmac]

OK, I feel like an idiot! It looks like my impulse Barb going into the intake manifold was clogged! I can’t believe it even ran! It was so plugged it would barely flow air at all, It would likely run fine cleared out, but I’m going to put the larger Barb on, Hoping this will fix my problems! LOL

It looks like a piece of Loctite from when I installed the barb originally,The weird thing is I was able to pressure vac test it and it free flow then, it must’ve broken loose and lodged itself in the 90 once I got it running

 

[NPKenny]

The easy fixes are always welcome around here!!!! Let's see it running again!

 

[Bigmac]

Got it up and running again! Now I can smoke out the neighbors! LOL it’s gonna take a little while to dial the carburetor in, but now it’s plenty rich

 

[Bigmac]

Impulse fixed and fat tune