McCulloch Chain Saws

[Maintenance supervisor]

Or bad spark?

 

[PogoInTheWoods]

I've been leaning toward a timing issue with this saw over on the MM thread, myself. Leaning out that L screw could possibly help the flooding unless the seat or needle are deformed. Then again, it did backfire pretty hard last time running if I'm not mistaken, so...

Maybe getting some additional input over hear could shed new light.

 

[edju1958]

I've come to the conclusion that therte are other saws more deserving of my time than those little MM saws.I think old Bob McCulloch decided to screw with the general public's mind when he ,or his engineers designed them.

 

[MacAttack]

I've been leaning toward a timing issue with this saw over on the MM thread, myself. Leaning out that L screw could possibly help the flooding unless the seat or needle are deformed. Then again, it did backfire pretty hard last time running if I'm not mistaken, so...

Maybe getting some additional input over hear could shed new light.

Right now my head is at a carb issue, the last time I had it running it flooded a lot more than a saw ever should. I never put the choke back on, and yet once it gave up trying to start (i was already pulling it with the throttle wide open) I took off the air filter, tilted it on it's side and a good 6 or 7 drops worth of gas ran out the carb. That just doesn't seem right unless I have a leaky inlet seat or a leaking welch plug.
I have another MDC carb on my bench that I put new diaphragms and gaskets in (not a check valve though) that I could try swapping into it to see what happens. I also have a plastic recoil pulley out of a junk 160s that looks like I can use, even though it's designed for the better recoil pawls, I've found they'll work for a long time one the narrow recoil pawls on the flywheel.

 

[GoBigRed]

I have had one instance where the metering lever was set correctly, but it still flooded. This was an SDC carb. I took it apart, checked it, ultra sonic cleaned it a million times, back together, but the same flooding result. So I set the needle lever a tiny bit lower than what the gauge indicates is the correct height, and then the carb worked correctly.
I’ve only done the walbros on my Macs and Homelites and that only about ten saws. But this was the only carb from any small engine I worked on that needed the lever set lower and then it held and metered fuel like it should

 

[MacAttack]

That's interesting! I'm very apprehensive about bending the metering lever because they are NLA and hard to find, for a stupid tiny piece of metal. I might try needle adjustments and sealing the welch plug. If that all fails I might set the metering lever even lower. Thanks!

 

[GoBigRed]

What carb is it? You can get kits for most carbs off Amazon for about $7. I think I have about half a dozen spare levers just for the SDC and HDC alone On those carbs they are easily adjustable. Even on the husky/Poulan power equipment I have the needle level is adjustable. I think you would be okay maki by a small adjustment. All I did was lightly hold the needle in place and pushed down on the levers tab where the diaphragm hooks in to. It wasn’t much and gave it just enough pressure to keep it closed

 

[Yokosukadweller]

A few questions on fuel supply:

I got an SDC-18 carb on the CP70 saw that fires but won't keep going. I replaced the sparkplug on it and it improved. But still did not successfully really start, although there is 'explosion' on every pull.
I've got some SDC-10 carb kits from Ebay. Do you think those will fit an SDC-18 carb as well? I can't seem to find the right info online. I also think the idle and H/L adjustments are probably off. Can H/L adjustments cause the lack of starting also?

 

[Yokosukadweller]

Perhaps the rubber rod 'snubber' that goes between the throttle and choke rods (thanks for correcting me on the terminology, Ed) is too close to the button end of the rod -- or possibly missing?

View attachment 921500​

Thank you @PogoInTheWoods - yes actually I had the snubber kind of stick and repositioning it helped with a sticky trigger. Still the choke button issue remains, but gradually trying to fix this issue and the fuel supply challenge.

 

[MacAttack]

What carb is it? You can get kits for most carbs off Amazon for about $7. I think I have about half a dozen spare levers just for the SDC and HDC alone On those carbs they are easily adjustable. Even on the husky/Poulan power equipment I have the needle level is adjustable. I think you would be okay maki by a small adjustment. All I did was lightly hold the needle in place and pushed down on the levers tab where the diaphragm hooks in to. It wasn’t much and gave it just enough pressure to keep it closed

It's a Walbro MDC, I have not seen any rebuild kits that include the metering lever. This carb has everything else new (diaphragms, gaskets, needle, check valve...)

 

[Yokosukadweller]

Or bad spark?

Not sure if that was directed at me, but it's relevant and I am checking whether it is (hopefully) the sparkplug or (worse) timing or electricity issue. Thank you MS.

 

[Yokosukadweller]

I've had the same issues with the choke lever that hooks into the eye/loop coming unhooked too.The choke rods are not easy to bend,but can be done.You'll need a pair of heavy duty needle nose pliers,or a needle nose vise grip to close the hook a little so it'll stay hooked on the loop.Don't crimp it too tightly though.If you happen to crimp it too tightly you can spread it open again with a screwdriver.Since the rod is made of a specially hardened steel,it's possible that it may break.

Yes I am trying this, that steel is pretty stiff! And I am trying to avoid having to take the entire tank off so there isn't much space to do the adjustment. I think I recall later 10-series setups had a different arrangement where the connection was accessible from inside (not under) the airbox. Much easier that way I think.

 

[heimannm]

Mac - Don't be nervous about adjusting the metering lever, I have an ample supply but have never had one fail from making adjustments.

Simon - K10-SDC is the kit number and will fit all SDC carburetors. Set both H and L around 1-1/4 to 1-1/2 turns open from lightly seated. Once you have it running you can adjust them leaner as needed.

Mark

 

[Yokosukadweller]

Update - fiddled with the idle and the H/L screws, now the saw starts and idles for 10-15 secs, its a bit rough. squeezing the trigger makes no difference in revs. I observe a bit of fuel coming out through the closed top of the carb (strange), and also can observe some amount of unburnt fuel leaking out of the muffler. I am a noob obv on this, but this seems there is too much fuel coming, the carb needs some adjustment or maybe cleaning? I've cleaned motorcycle carbs before, but am yet to try rebuilding a chainsaw carb. Maybe this is my time to do it?

 

[knightmax]

Hey gang, My homemade carb vac check gauge/rig died. I know I have heard you guys mention commercial vac kits for testing carbs as well as other issue with the saws here before. Whats the right one for me to get? tnx.

 

[heimannm]

Simon - Did you have the piston out of the SP70? Is there a chance you put it together with the piston turned around? The skirt is wider on the intake side than the exhaust side and if it is turned 180 degrees the narrow exhaust side piston skirt will not close off the intake port. If that is the case you have to completely disassemble the saw but rather than pressing the wrist pin out to turn the piston around, disconnect the connecting rod from the crankshaft and turn it around; this avoids any unnecessary pressing the wrist pin out and in.

Mark

 

[edju1958]

Update - fiddled with the idle and the H/L screws, now the saw starts and idles for 10-15 secs, its a bit rough. squeezing the trigger makes no difference in revs. I observe a bit of fuel coming out through the closed top of the carb (strange), and also can observe some amount of unburnt fuel leaking out of the muffler. I am a noob obv on this, but this seems there is too much fuel coming, the carb needs some adjustment or maybe cleaning? I've cleaned motorcycle carbs before, but am yet to try rebuilding a chainsaw carb. Maybe this is my time to do it?

Chainsaw carbs are not difficult,trust me as I was very doubtful of myself.There are people here who can help you through the process.All you need to do is ask.

 

[GoBigRed]

Simon - Did you have the piston out of the SP70? Is there a chance you put it together with the piston turned around? The skirt is wider on the intake side than the exhaust side and if it is turned 180 degrees the narrow exhaust side piston skirt will not close off the intake port. If that is the case you have to completely disassemble the saw but rather than pressing the wrist pin out to turn the piston around, disconnect the connecting rod from the crankshaft and turn it around; this avoids any unnecessary pressing the wrist pin out and in.

Mark

Quick question Mark. Is this the same for any 10 series saws? I’m having issues with a saw I put a new piston in and it didn’t have the typical arrow that most two strokes have. So I just put it in and figured it didn’t matter

it sure should explain the problems in having especially after porting the exhaust side a little and now having the wrong skirt width opening and closing that port.

 

[heimannm]

Many of the earlier saws have full skirts on the pistons so it doesn't matter. From the 6-10 to the 7-10 they changed the pistons to the windowed type. I think any SP model (60, 70, 80, 81) and all of the PM models (55, 55, 570, 700, 850, 800, etc.) will have a windowed type piston skirt. I am not sure if/when the 10-10 models went from a full skirt to a windowed type.

The windowed pistons normally have "ex" cast into the piston to help you locate it correctly, but you have to look at the piston pretty carefully to notice it.

Mark

 

[emf123]

The windowed pistons normally have "ex" cast into the piston to help you locate it correctly, but you have to look at the piston pretty carefully to notice it.

Mark

It's easy to mess up even when you know to look for it. For some reason, when you're working on it upside down and putting the rod on the crank when the piston is down on the bench, it's easy to lose the orientation.

Eric