McCulloch Chain Saws

[buzz sawyer]

These carbs don't work under spring pressure but the fuel itself. The fuel fills the carb chamber from the fuel pump under the tank operated by crankcase pulsations and rises against the diaphragm which raises the arm and ball assembly closing off the flow of fuel.

The idle is mixed with air from the top half of the carb chamber with fuel and is drawn from the bottom half up through another tiny hole into the housing through the throttle gate and into the venturi through the rotary valve into the crankcase. Much unlike your more modern saws. I'd recheck your Lowe half to make sure the arm and ball are seating OK with no debris keeping the fuel from shutting off.

Nick


The mixture screw on these is air only and in is less air, more fuel. The lever adds more fuel into it for high speed operation.



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Thanks Nick. I've had the ball and seat apart several time and all looks good. I'm wondering if I may have the metal orifice plate (47) on backwards or the idle mix screw is too far in. See attached - my plate has three large holes (I added the yellow one) and one very small one. I have it on the way it shows in the drawing. Hoping that correcting the idle mixture screw will correct it.

 

[Nickolas]

Thanks Nick. I've had the ball and seat apart several time and all looks good. I'm wondering if I may have the metal orifice plate (47) on backwards or the idle mix screw is too far in. See attached - my plate has three large holes (I added the yellow one) and one very small one. I have it on the way it shows in the drawing. Hoping that correcting the idle mixture screw will correct it.

From a bulletin they eventually did away with those original gaskets that had the screen in them along with that plate. It doesn't take much to clog the fine wire mesh in it and then another reason your saw won't run right. Lots of issues with these back in the day. There are several possibilities so it's a trial and error process.

These saws are all I mess with anymore but I mainly run a 4-30a and a 77. I've got those two running like a fine watch. I always tear them completely down and make new gaskets, replace seals , rebuild carb, fuel pump and then a nice leak free machine. They can be finicky at times but patience will pay off..

My favorite 3-25 two button saw. Runs in great shape but will never see wood for being too rare...

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[rwoods]

Brian and I did a little cutting down at the wood lot with our 800s. I was going to have his son make a video of us cutting side by side on a 3 1/2" red oak - just wanted to finish bucking a 30" log first - then the 800 started making a vibrating hum. Shut it down to find the muffler and DSP valve off. The heat and vibrations destroyed my homemade aluminum spacer and broke the safety wire. Fortunately nothing appears to have been ingested though all of the spacer is not accounted for. I guess I'll have to buy the factory bolts and locking strap plus something to keep the DSP valve tight.

Ron

 

[Brian Thacker]

Cutting with the PM 800. Ron in the background with his PM 800.


Not a good picture took with my old flip phone.

Brian

 

[Brian Thacker]

I was watching National Lampoon's Christmas Vacation. I could not see that well but it looked like the chainsaw that Clark used to cut the tree down is a Mac 610.

Brian

 

[buzz sawyer]

Sent from my 0PM92 using Tapatalk[/QUOTE]

I was watching National Lampoon's Christmas Vacation. I could not see that well but it looked like the chainsaw that Clark used to cut the tree down is a Mac 610.

Brian

I believe you are correct.

 

[buzz sawyer]

And now................

https://www.ebay.com/p/Chainsaw-Cla...n-8-Clothed-Movie-Figure-NECA-2017/2194177046

 

[Brian Thacker]

Yep, Looks like a PM 610. Might be a must for Christmas.

 

[buzz sawyer]

Thanks Nick. I've had the ball and seat apart several time and all looks good. I'm wondering if I may have the metal orifice plate (47) on backwards or the idle mix screw is too far in. See attached - my plate has three large holes (I added the yellow one) and one very small one. I have it on the way it shows in the drawing. Hoping that correcting the idle mixture screw will correct it.

I believe I found the problem. Everything is assembled correctly. The plate can only go on one way. See attached. I made a plate to replace the upper chamber of the carb so I could pressurize the diaphragm and it is leaking under the clip under pressure. If I lift up on it slightly it bleeds off VERY slowly but when I release it, it bleeds out quickly.

 

[ChoppyChoppy]

250.

 

[ChoppyChoppy]

250.

 

[ML12]

Got my SP-81 back together, noticed that it has a weird version of the SDC carb in it (only one adjustment other than idle speed).
But it runs great and has enough compression that without the compression release I can barely turn it over.

 

[ML12]

Also had some time to try and figure out a carburetion issue on another mac saw, the 1-72. Seems no matter what settings I had, fuel would just pour out the carb throat. I replaced the needle and seat and it had new diaphragms. So I gave up and swapped in a known good carburetor, only to experience a massive fuel leak from somewhere else in the carb box. whatever. I will fix it another day. Or order another Chinese HL carburetor to put on it.

Excuse the husky in on the bench, it was also getting some work done.

 

[PogoInTheWoods]

My SP81 originally had that carb. It was used on serial numbers with prefixes 11 and 12 which also used a different tank. I messed up something (can't recall what) rebuilding the carb and decided to go with a fully adjustable one since I had a large venturi version available and also had to change the tank (thank you Mark) to accommodate the adjustment screws.

Still haven't gone back to it and figured out a timing issue, but like yours, it has unreal compression and I'm afraid of breaking the rope or starter pulling it over enough to get a good compression reading.

And that Husky is perfectly excusable.

 

[BigBlue]

Is that 1-72 a giant sized saw or is it just the camera's perspective that makes it look so much larger than the 10-series sized saw to the right of it on the bench??

Rob

 

[ML12]

Is that 1-72 a giant sized saw or is it just the camera's perspective that makes it look so much larger than the 10-series sized saw to the right of it on the bench??

Its partly perspective and partly just a larger saw. The 1-72 is in a vise about 10" in front of the sp81. The older large frame saws are dimensionally pretty big compared to more modern saws.

 

[Walter Glover]

ML12, love your SP81! Fine looking saw there. Love those series 10 Macs. Look forward to seeing it in some big B.C. wood eh? Around here a 20" bar can handle anything that needs cutting.

 

[HeRoze]

Hey - I hope this isn't a foul, but if you know anyone that can travel to GA I'm getting rid of a lot of saws, mostly Macs
Link: Want to Sell - Instant CAD

 

[dynodave]

My BIL brought me another saw yesterday from his town transfer station.
1999??? Mac Timber Bear ?mod 60013414 SN11-059617-
?55.5cc? acres site is not clear about bore/stroke on this model-
20"-3/8-70dl- PHO 14lb15oz
sorry have not put a pix in my gallery yet. Not all beat up, looks clean
170psi...oily residue in tank, came with new tygon 4040 line from filter to carb. I then half filled with fresh mix. primed in carb and fired it, repeat 3 times. Finally ran on tank fuel... felt strong and as expected LOUD.
Ran it for 20-30 seconds and it never seemed to put any oil on the bar. Does it need a new oiler diaphragm? any corrections or suggestions about typical failure of oiler.
TIA

 

[Walter Glover]

Pics would be great.
Oiler should be gear drive which can fail. Tabs on oiler gear are weak esp if thick summer oil used in winter.
I have a 4600 mac that the tabs are nearly gone so thinking that was the issue.