McCulloch Carburetors

[heimannm]

1 to 1-1/4 turns out from lightly seated for both H and L is a good place to start.

If the saw has been setting for a long time it might help to give it a shot of prime right down the carburetor, then try pulling it with the throttle wide open. Sometimes you have to prime it and get the short burst two or three times before the carburetor starts pulling fuel on it's own.

That saw will have a pop up compression release, if it is leaking too much the saw may fire but not stay running. I have had some success fixing a leaking pop up with a dap of valve lap compound or even rubbing compound and polising up the valve and seat. Make sure you clean everything well before you put it back together.

Mark

 

[wendell]

Thanks, I'll give that a try.

 

[WKEND LUMBERJAK]

Subscribing

 

[dieselsmoke]

Hellow Mark, I'm adjusting the mac carby on my newest saw, a Mac 790. This one has the Idle spring, tho it's not adjusted right. Shouldn't the tiny spring be pulling the throttle plate open, against the V shaped link on the end of the throttle shaft? when the saw is stopped and hands off the trigger? This is the first time I've tried to adjust this linkage. Thanks in advance. Brad.

 

[Eccentric]

Hellow Mark, I'm adjusting the mac carby on my newest saw, a Mac 790. This one has the Idle spring, tho it's not adjusted right. Shouldn't the tiny spring be pulling the throttle plate open, against the V shaped link on the end of the throttle shaft? when the saw is stopped and hands off the trigger? This is the first time I've tried to adjust this linkage. Thanks in advance. Brad.

You've got it Brad. The spring should pull the throttle plate open. When the engine's running at idle, vacuum will pull the throttle plate shut. The trick is finding the correct ballance. The throttle possiton will 'float' slightly. If you have the spring set with too much tension, the engine RPM will bounce excessively at idle. Too light, and it will tend to slow down and die.

 

[dieselsmoke]

You've got it Brad. The spring should pull the throttle plate open. When the engine's running at idle, vacuum will pull the throttle plate shut. The trick is finding the correct ballance. The throttle possiton will 'float' slightly. If you have the spring set with too much tension, the engine RPM will bounce excessively at idle. Too light, and it will tend to slow down and die.

Thanks Aaron, I missed this reply on the 17th. Played with spring settings the other nite, the saw is still not happy, so today I have re-read this entire post. I plan to make a final adjustment tonight and mount the carby for a test. This thread is really helpful, "a picture is worth a thousand words " thanks to everyone.

 

[cpr]

Stick with it, it's rewarding. I must've had one in and out of saw 30 times and then spent the better part of an hour fiddling with the spring, the travel limiter and windmilling needles. Now that it's set though, it works great.

 

[Brian13]

Stick with it, it's rewarding. I must've had one in and out of saw 30 times and then spent the better part of an hour fiddling with the spring, the travel limiter and windmilling needles. Now that it's set though, it works great.

Same here, and still dont think I have the spring tension just right.

 

[cpr]

Yeah, mine probably surges and hunts just a little too much, but I like it doing that.

 

[Brian13]

I think I have the spring tension set a little too high. Dosnt want to come down all the way to idle, sticks on like a high idle, but once you get it to come all the way down its fine. So I am thinking the spring is pulling to hard for it to close like it should.

 

[dieselsmoke]

Thanks guys for the help, I was cleaning the S-250 the other nite and found it Has a flatback with a choke butterfly. I had never looked that close befor, assumed it was a tilly HL. So, in I went. The PO had pinched the throttle arms tight to the rod, no "play" allowed. And they had rotated the gov spring the opposite direction so it closed the throttle butterfly. A quick tweek with the screw driver and adjust the spring the other way and presto, idle govener. this saw really responded well to the idle govener, It really works.

I;m still searching for the right combo on the 790 tho. I'll get it yet.

 

[heimannm]

It is satisfying to fix something, or make it "right" again, and have the machine respond as it is supposed to.

Congratulations on the Super 250, I am sure you will enjoy that one.

Mark

 

[Sawchips]

Great thread!!!
All of your work is appreciated, "Thank you Mark" and the rest of you that contributed input.

Back in March a couple of you (CPR & Stinkbait) were getting ready to swap out the check ball assemblies in the carbs you were working on. How did that go?
I'm going to have to do something with mine (Super 250) and I can't seem to find a new check ball, so I'm going to try and get mine out with out messing it up to bad. If I can do that I might be able to revers engineer the thing and make a new one. Of coarse I'm saying this with out have a clue as to what it looks like.
Did any of you happen to take any pictures of the check ball assembly or the bore in the carb body? Knowing what it looks like on the back side would help keep me from making a complete mess out of it.

Thanks
Bob

 

[Sawchips]

Bump.

 

[heimannm]

The check ball and seat are sold as a kit (61155) or individual components ball (61151) and seat (61152).

Try Bob Johnson (607 638 9297) for the parts, don't give up if you don't connect the first time or two that you call.

Note that you will need a 1" expansion plug for some of the carburetors (check valve is under the plug). It seems to me that some carburetors may have a threaded plug rather than the expansion plug but that could be a feeble old mind playing tricks on me.

Mark

 

[Sawchips]

No Joy on the check ball assembly.
Bob says someone from California bought out his remaining stock last week. He still has the expansion plugs, and the check ball it self.
I'll try using some carb cleaner on mine and see if I can get things moving with out taking it apart.
I still think I can make new seat cover plates, just need a "take out" that isn't to badly damaged.

 

[Eccentric]

No Joy on the check ball assembly.
Bob says someone from California bought out his remaining stock last week. He still has the expansion plugs, and the check ball it self.
I'll try using some carb cleaner on mine and see if I can get things moving with out taking it apart.
I still think I can make new seat cover plates, just need a "take out" that isn't to badly damaged.

Wasn't me. I swap 'em out for Tillotsons. I had thought about getting a couple sets to rehab the flatbacks sitting on my shelf though. It was a low priority....

 

[Sawchips]

Wasn't me. I swap 'em out for Tillotsons. I had thought about getting a couple sets to rehab the flatbacks sitting on my shelf though. It was a low priority....

We'll let you off the hook you were the first person I thought of.

The culprit was working on a 660, Bob thought.

 

[Eccentric]

We'll let you off the hook you were the first person I thought of.

The culprit was working on a 660, Bob thought.

Ha!

I figured I'd be a prime suspect. I don't have a 660 either (although I DO have a 650 that's now Tillotson HL63 equipped). I think I know who it might be......as he is in ca and owns at least one 660. It's not who you think either. Not gonna give him up however...

 

[Sawchips]

Ha!

I figured I'd be a prime suspect. I don't have a 660 either (although I DO have a 650 that's now Tillotson HL63 equipped). I think I know who it might be......as he is in ca and owns at least one 660. It's not who you think either. Not gonna give him up however...

No need to rat him out......not yet anyway:msp_smile: I ran some carb cleaner through it tonight. That changed the ball color from a gooey looking black snot to a clean off white color, and it now moves freely. Also got a good stream of cleaner through the venturie booster while spraying through the seat orifice. Should be good to go. I forgot to take pictures tonight, but I'll make sure to get some during reassembly, and then post them. I'm sure it will help the newbie's that find this string.