McCulloch Chain Saws

[Jeffrey F.]

I was very kindly given a Tillotson carb kit along with a printout of a McCulloch Flatback shop manual by Jeff today, thank you sir!

so I'm looking through the pages and what's this?? A rubber one-way duck valve in the impulse passage? If this is located somewhere inside my Mac Flatback carb, it is almost certainly hardened up and my guess is not allowing the crankcase pulses to make the carb function properly....

View attachment 1218496View attachment 1218497
Sorry about that thought maybe book would help
View attachment 1218498

 

[MacAttack]

The book is very interesting! Lot's of good info about the theory on those carburetors.

I'm guessing the flatback and pressure pulse carbs work on very similar principles, they appear very similar.

 

[Okie]

Macattack:

more hands on experience with Mac's

referring to post 49,916 about carb pulse priming (getting gas to the engine)

One thing I like about the HL Tilly carbs is if you suspect the fuel pump is not working the air box cover STUD that is on top of the carb is also a fuel pump test port.
Mac had a test barb that screwed into the top of the carb after the existing stud and COPPER SEALING WASHER is removed and a low pressure gauge (10 lbs or so) could be attached to the stud and as the engine is cranked several times (about 10 times) the gauge should show some pressure of around 1/4 to 1/2 lb EVENTUALLY as the engine is cranked. Do not remember the exact specs for pressure but main thing is if any pressure is noted the pump is sending gas to the carb.
I've made a test barb using a threaded stud and drill a small hole in the stud for attaching a pressure gauge.. Also a hint that the saw is not getting gas is if you removed the stud and the port hole is dry the carb is not pumping any gas. (the stud threads into the carb top are standard SAE fine threads nd the test port can be made from a bolt)

Also the majority of my 1-40 through 1-50 Mac saws start easier when the carb throttle is wide open, both cold and hot. To do such I place the saw on the ground and hold the throttle open with my shoe toe OR I take a #10 gauge SOLID copper wire and make about two turns around the handle and throttle trigger to hold the throttle open and when the saw starts just push the wire down and leave it one he handle.
I seen on this site sometime back where a guy installed a throttle advance on his old Macs but do not remember the suggestion.
The old Mac's when they start do not high rpm scream and are slow coming up to speed therefore more time to come back to idle when the saw starts.
On a cold Mac I usually at first just try manually manually priming them through the muffler and not have to removed the air box cover.

 

[MacAttack]

Okie,

Thank you for that excellent write-up! Very useful info on the HL Tilly carbs.

I'm hoping to have time tonight to start putting my HL back together, I'm very cautiously optimistic this will get my 450 running.

I also got some parts from Mark yesterday for my build that I will share later.

 

[MacAttack]

Stack muffler and NOS top cover courtesy of Mark Heimann. This saw sure looks different from when I got it.

 

[Okie]

The stack mufflers have a neat sound AND it's easy to give the engine a prime with a stack muffler.

 

[MacAttack]

The stack mufflers have a neat sound AND it's easy to give the engine a prime with a stack muffler.

I call it the "harmonica" muffler haha. Pure simplicity.

 

[Squareground3691]

Some Kart action,

 

[flatsfisher]

finally got to work on the PM1000. media blasted and primed. had about a 9 or10 day period where I was recovering from a southern black widow bite. knocked the hell out of me. some really weird and interesting symptoms.

 

[flatsfisher]

inside the top cover is this very thin aluminum plate that is pinned to 2 small posts. it has apparently vibrated in half over the years. does this have to do with winter vs summer temps? do I need to make a new one or just get rid of it? I'm in florida, so no winter here. it is shown in both the PM1000 and P100 IPL's but neither IPL gives part names, only numbers. google didn't yield any clues.

 

[MacAttack]

I'm starting to suspect I have a coil / weak spark issue going on with my 450. On the bright side, I finally got it to run, long enough to take a video. It took a LOT of pulling over to get it running, and I flooded it a couple times, like it just couldn't quite muster up enough spark to burn the fuel and start.
Not long after I stopped recording though, it seemed like I lost spark. The engine missed a few times, and then stopped like you hit the kill switch. I pulled the plug to check for spark, it would spark but only when the engine was pulled over quickly, not like a Mac normally sparks even at lower engine speed. Also, as I think about this more, the original engine was SO packed with sawdust, it had to have been running very hot, which can break down a coil. It's very possible the reason this saw was shelved long ago was a failing coil....
Here's the video. I think my next step is a coil-swap with my Mac 250 parts saw and see what happens.
At least I have SOMETHING to show for this ordeal....

 

[MacAttack]

Scavenged coil:

Can anyone tell me what resistance values I should be measuring on the primary and secondary coils? According to my service manual there were multiple different coils and values.

It's got .6ohms on the primary coil.

 

[heimannm]

My notes say:

Large Frame Points Ignition

Resistance – 0.6-1 Ω Primary

4-10 K Ω Secondary

Inductance – 8.5-10 H (henry) Secondary

2.5-3 mH Primary

Mark

 

[MacAttack]

Thanks Mark!

The coil that was in the saw shows .5ohms on the primary, which I don't think would cause the running issues??

I'm getting more convinced all the time I have a spark issue. I'm going to test and install the backup coil tonight and see what happens.

 

[heimannm]

Our meters have a pretty hard time distinguishing between 0.5 and 1.0 Ω ... I don't think that would be a problem in your case.

I would check the points again, and clean them with some fine emery or crocus cloth followed by several swipes with clean paper.

Also confirm your point gap is around 0.018".

Mark

 

[serdie]

My notes say:

Large Frame Points Ignition

Resistance – 0.6-1 Ω Primary

4-10 K Ω Secondary

Inductance – 8.5-10 H (henry) Secondary

2.5-3 mH Primary

Our meters have a pretty hard time distinguishing between 0.5 and 1.0 Ω ... I don't think that would be a problem in your case.

I would check the points again, and clean them with some fine emery or crocus cloth followed by several swipes with clean paper.

Also confirm your point gap is around 0.018".

Mark

I chipped all my large framed Macs it worked out really well. I think the chips were $15

 

[MacAttack]

Our meters have a pretty hard time distinguishing between 0.5 and 1.0 Ω ... I don't think that would be a problem in your case.

I would check the points again, and clean them with some fine emery or crocus cloth followed by several swipes with clean paper.

Also confirm your point gap is around 0.018".

Mark

I cleaned the points with a piece of cardboard when I had it apart....I'm always nervous about cleaning points too aggressively and losing their flatness...but I may have to anyway. That's what I'll do if I still have a weak spark after the coil swap.

 

[Squareground3691]

I cleaned the points with a piece of cardboard when I had it apart....I'm always nervous about cleaning points too aggressively and losing their flatness...but I may have to anyway. That's what I'll do if I still have a weak spark after the coil swap.

Fine grit emery paper works then clean,

 

[MacAttack]

Fine grit emery paper works then clean,

I've got some 400 grit, is that fine enough?