McCulloch Chain Saws

[Maintenance supervisor]

Do all SDC carbs have the nozzle diaphragm in them.

Nozzle as in check valve port for high speed?

 

[Brownthumb]

Nozzle as in check valve port for high speed?

Yes, I just rebuilt a carb and had a idle issue. Before and after carb rebuild same problem.
I dident check the nozzle when i had her apart. Tore her down again and checked her and there is no rubber disc in her. I put in a new nozzle and she runs the same.

 

[vizette]

They say you learn something new everyday, and boy is that the truth. For YEARS I wondered how Mini Macs functioned without a gas tank vent or vented cap, which there was no sign of. I always assumed maybe the cap just leaked enough to let in air.

Today, I learned they vent through a PINHOLE in the top of the tank. I almost didn't believe it until i examined one and sure as s--t.... that's a pin sitting in the tiny vent hole.

LOL funny you brought this up - I was randomly thinking about this earlier this week when I was working on a Homelite and was looking at the duckbill in the gas tank. The same thought crossed my mind; how does my 110 vent? Also had the same assumption about the cap!

 

[fossil]

Yes I can, I have that manual and it shows both diaphragms numbers 24 and 25 but it doesnt specify when or if they a re both needed. I know I've assembled a ton of SDC carbs with only one. And I think I remember the pump cover dictating thick or thin gasket.

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Hi Kevin. I had always thought the steel cover on the pump side meant no check valve diaphragm and a thick pump side gasket.
I did a little research and that is not necessarily so. You can always get the info from the Walbro site.

I made a list up which is not complete but will likely meet your needs of which carbs use the thick pump side gasket and which require the check valve diaphragm.

Attached

 

[Maintenance supervisor]

Yes, I just rebuilt a carb and had a idle issue. Before and after carb rebuild same problem.
I dident check the nozzle when i had her apart. Tore her down again and checked her and there is no rubber disc in her. I put in a new nozzle and she runs the same.

Ok you must have the rubber/ disc valve in your sdc , under the brass insert and screen , it meters fuel with the venturi vacuum, basically you have a open hole when the throttle is pulled open and it will not run right ,usually they will idle though ?
Tillotson's do not have a diaphragm just the screen to delay fuel flow.
Some sdc carbs have a brass screw in valve with a tan check valve instead of the Welch plug.
Basically if you remove the welch plug and shine a flashlight through the carb and see light in the valve it's bad. Although I have seen them all bunched up and gooey.

 

[Brownthumb]

Ok you must have the rubber/ disc valve in your sdc , under the brass insert and screen , it meters fuel with the venturi vacuum, basically you have a open hole when the throttle is pulled open and it will not run right ,usually they will idle though ?

The saw runs the same with or without it. That’s why I asked.
Usually I find some remnants of it. The saw cuts great but idles down over a few minutes and stalls.

 

[Maintenance supervisor]

The saw runs the same with or without it. That’s why I asked.
Usually I find some remnants of it. The saw cuts great but idles down over a few minutes and stalls.

If fuel is leaking down from the Welch plug it might be getting some fuel to run and then richening up at idle and dies.
Either way it could lead to a high speed lean and then wouldn't it have been cool to change the 5$ check valve and not smoke your saw?

 

[RolandM]

Hi Kevin. I had always thought the steel cover on the pump side meant no check valve diaphragm and a thick pump side gasket.
I did a little research and that is not necessarily so. You can always get the info from the Walbro site.

I made a list up which is not complete but will likely meet your needs of which carbs use the thick pump side gasket and which require the check valve diaphragm.

Attached

Thanks from here too.. I have an SDC 44 on a ProMac 555 which has developed a big flat spot off idle, and I am assuming nozzle check valve. Job to do sometime, robbed a carb from a parts saw which runs OK for now. I like this 555 for quartering up unsplitable chunks, fitted with with just a 13" bar and .325 chain. Its had some work to do, just had a 5L can of fuel through it over last few weekends, I suppose you work out which tool is best for a particular job, and this tweaked 555 is great.
A carb made in ~1977, probably never opened before, its time for a good service!

Roland.

 

[2broke2ride]

I was able to sneak away today for some saw time. I got the carb reassembled on the SP81 today and finished putting the saw together. I am happy to report that it oils with both the auto and manual oilers and it fired right up and seemed to tune well. I am however having a problem getting the oil tank cover to seal. I might need to resort to some Dirko. I even cut a new gasket and no joy.
I have not had a chance to get it in wood. I have a 28 inch power match bar on the way for it.
I ran the PM700 today also bucking some large oak. It ran well but the full comp chain on the 28 inch bar is filed a bit too aggressive for it. I will have to leave the rakers for the next couple filings.

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[vizette]

I gave Lee at Lil' Red Barn a call and got a bunch of parts including a 24" bar with full chisel full skip chain and a tune up kit.

I've been eyeing their 28" bar on feebay for a while - how'd it seem quality wise? I was wondering if it was just like a re-hashed archer bar or something. That said I've seen not horrible things said about archer bars, just curious what lrb is using.

 

[vinnywv]

I was able to sneak away today for some saw time. I got the carb reassembled on the SP81 today and finished putting the saw together. I am happy to report that it oils with both the auto and manual oilers and it fired right up and seemed to tune well. I am however having a problem getting the oil tank cover to seal. I might need to resort to some Dirko. I even cut a new gasket and no joy.
I have not had a chance to get it in wood. I have a 28 inch power match bar on the way for it.
I ran the PM700 today also bucking some large oak. It ran well but the full comp chain on the 28 inch bar is filed a bit too aggressive for it. I will have to leave the rakers for the next couple filings.

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I had a leaky oil tank lid before. Did the same things youve done. Turned out that some cocers have a little lip on them on the bar side. It wont seal flush. So i took it to a belt sander and just sanded that lip down gently. Its magnesium so its soft. My leaky cover problem was solved. Thats just my experience. Something for you to check.

 

[Maintenance supervisor]

Had a recommendation from someone in another thread to post these pictures here. My dad picked up a PM650 at a yard sale for $20-it was clean as a whistle and the gas tank was dry as a fart. I ran it for a while with the 18" bar it came with but I needed something that would handle some bigger wood. I gave Lee at Lil' Red Barn a call and got a bunch of parts including a 24" bar with full chisel full skip chain and a tune up kit. I'm running it on 50:1 (my other saws are both Stihls) 100LL fuel which it seems to like so far. I also have a PM610/Eager Beaver that runs which I might put the old 18" bar on just for some variety. What is the operative difference between these saws since they are apparently both 60cc? Is it just the carb and/or the tuning? All shined up and 24" bar and skip chain fitted:

Some of this week's bucking and splitting. Finally got around to working on some of the locust and cherry that fell during the "Four'Easters" in 2018-this is only about half of it. The trunks are about 20-22" in diameter so the 24" bar really helps. Looking forward to browsing this thread more and hopefully learning the difference between a 610 and a 650 as well as what parts interchange:

If you want , you can flip the spikes around (top to bottom) for the factory setting, unless you prefer them as is.

 

[IHDiesel73L]

I've been eyeing their 28" bar on feebay for a while - how'd it seem quality wise? I was wondering if it was just like a re-hashed archer bar or something. That said I've seen not horrible things said about archer bars, just curious what lrb is using.

No idea what it really is. There is just a series of number stamped on the bar near the bolt holes-no other markings. So far so good. I've heard bad things about other low cost aftermarket bars such as the chain guide being too wide resulting in a poor fit, etc...but that is not the case here. It cuts nice and straight-as a matter of fact I'm currently using this saw to freehand mill some walnut slabs from a tree we had come down:




I found LRB's customer service to be excellent as well. The 24" bar and chain combo for this saw offered on the website is full compliment, but I called up and they switched it to full skip, no extra charge, etc... They have parts for literally everything-its all made in China but the fit and finish is decent, and its cheap. I will definitely be buying from them again.

If you want , you can flip the spikes around (top to bottom) for the factory setting, unless you prefer them as is.

LOL...thanks. I've owned this saw for about 10 years and never knew they were upside-down!

 

[Aaron Rybicki]

It’s kind of hard to see but does this look like it’s leaking? I sprayed soapy water around it and there are very very tiny bubbles near the inner rubber part of the seal when pulling it over. During the install, the seal kind of got bowed in slightly.

 

[Aaron Rybicki]

Also got my hands on a Super 797 finally!

 

[PogoInTheWoods]

During the install, the seal kind of got bowed in slightly.

That's usually not good and I'd say there's a leak.
Is the case pressurized with a test setup or are you just pulling the saw over?

 

[Aaron Rybicki]

That's usually not good and I'd say there's a leak.
Is the case pressurized with a test setup or are you just pulling the saw over?

Just pulling the saw over. It’s the correct seal but really didn’t want to go in. The bubbles are very small and hardly noticeable.

 

[Aaron Rybicki]

You can kinda see what I’m talking about.
Haven’t ran it yet to see because as I was attempting to start it, the rubber handle broke in half. Which is 100% my luck lol

 

[Maintenance supervisor]

You can kinda see what I’m talking about.
Haven’t ran it yet to see because as I was attempting to start it, the rubber handle broke in half. Which is 100% my luck lol

No good , replace seal, sleep better.

 

[PogoInTheWoods]

That needs to be straightened out. Get it as flat as possible with tapping on a washer slipped down the crank and then nudge it as necessary with a socket or drift around the edges until it as flat as you can get it without going any deeper than the deepest edge is now. You may get away with it if you're very patient and careful.