McCulloch Chain Saws

[MacAttack]

No fuel in the metering chamber....for some reason, either the pump or the inlet needle, I'm not getting fuel to the chamber.

 

[MacAttack]

Make sure the vacuum holes aren't plugged or blocked in anyway. I sounds like you aren't getting any pulse from crankcase.

I definitely have pulse at the intake manifold, I'm checking the carb passages.

 

[MacAttack]

Jeff! I think you're right!

Look....my metering gasket is flipped and blocking the impulse passage!

 

[MacAttack]

Welp....I got it to run for about a minute, then it seemed to run out of fuel. Gonna walk away for now and sleep on it...but that Tillotson is looking better and better all the time.

Edit: I took the plug out and it looked wet, so I'm trying to figure out if I'm having a flooding issue. I re-checked the metering lever height when I had it apart, so I'm struggling a little with diagnosing my issue. It sure seemed like I was running out of fuel versus flooding.

 

[heimannm]

Pressure test the carburetor to make sure your needle is seating and holding pressure.

Mark

 

[MacAttack]

Yeah, sounds like the flatback needs to come back out again. I may need to track down an inlet needle, I thought I had one but the one I have that came in a kit for an SDC is very different.

 

[Jeffrey F.]

Yeah, sounds like the flatback needs to come back out again. I may need to track down an inlet needle, I thought I had one but the one I have that came in a kit for an SDC is very different.

Flatbacks can be challenging but keep going. It sounds like you're on the right path. If plug is wet then you're getting enough if not to much fuel. As Mark said it may not be seating and flooding. Make sure you also have a new spark plug installed too.

 

[heimannm]

I wish we had known that yesterday...

Some of the MAC carburetors have a replaceable seat in the metering needle fitting and use the same rubber seat as the Tillotson HL carburetors...



This is from and HL but illustrates the principle. I show the needle, fitting with the seat, and the replaceable seat.



Some use a forked metering lever and the same rubber tipped needle as the SDC...this may have been an upgrade provided by McCulloch but I've found it on other carburetors that I've taken apart as well as the kits.





And yet others have a rubber tipped needle and no forked lever.





So many variables.

Mark

 

[MacAttack]

Yeah Mark, mine has the rubber tipped needle and no fork, I feel like the needle I came up with SHOULD work, I'll need to try pressure testing.

I've been wracking my brain all morning though, because based on my years of fixing small engines it SEEMS like I'm running out of fuel. I'm wondering if the electrode of the spark plug looked a little wet from priming the engine, even though it would run for a few moments and then run out of fuel....it's definitely not spattering fuel out of the cylinder when I pull the plug and pull it over.

It seems like I have a good impulse for the carb...if I had some issue with the reeds, would that diminish the crankcase impulse for the carb's fuel pump??

 

[MacAttack]

My problem seems to be 2-fold. The saw seems to want to flood, and once it's running it starves for fuel. I was able to get it running and keep it running for at least a minute or 2 by giving the primer a pump every 5 seconds or so. It seems like for whatever reason I'm not getting a sufficient volume of fuel to the metering chamber. But my fuel supply to the carb seems good, the primer is able to pull plenty of fuel. That's why I was wondering could I have a weak crankcase impulse??

This Mac carb is kicking my butt...running out of ideas, unless my needle and seat are the problem. I still need to do a pressure test, but then why is it starving for fuel.

 

[vinnywv]

I know it is crappy to give up on these saws....maybe try the tillotson and assure yourself you have a good saw. Once its good then revisit the other carburetor.

 

[MacAttack]

That's exactly what I'm going to do...if I rebuild the Tillotson and have the same issues, i know i have other problems. I'm really hoping I don't have an issue with the reeds, but I didn't notice ANY fuel spitting out the carb, so that might rule that out?

 

[sean donato]

If you pressure/ vac tested the same, and can confirm the impulse tract isn't blocked up, and the reeds looked reasonable/ weren't cracked/ bent up its usually a carb problem. Don't worry, I'm in close to the same boat with my flat back, expect I'm dead set it's getting the tilly whenever I have the free time to mess with it.

 

[MacAttack]

If you pressure/ vac tested the same, and can confirm the impulse tract isn't blocked up, and the reeds looked reasonable/ weren't cracked/ bent up its usually a carb problem. Don't worry, I'm in close to the same boat with my flat back, expect I'm dead set it's getting the tilly whenever I have the free time to mess with it.

I appreciate the moral support! Haha.

I had a date with "Tilly" tonight, all disassembled and cleaned and a rebuild kit on order. I'm not quite giving up on the flatback but I need to figure out if I have a saw problem or a carb problem.... the Tillotson is a beautifully simple carb.

 

[altatim]

Any idea what this is? D44, Super 44?

 

[heimannm]

D-44, the stamped steel AF cover and the shape of the flywheel housing are key indicators. The spark plug straight out the back of the cylinder is another giveaway. The A and Super A models had the spark plug moved towards the flywheel side and placed at an angle. I'm guessing that was to make it less vulnerable.

The model and serial numbers were normally stamped in a different location than you show but with McCulloch, being unconventional is never a surprise.

This is the conventional location, model number on the left and Serial number on the right.



See what I mean?



D-44, 44 Super, 44 Super, and 44 Super A.



The 44/55 Super A normally had the hockey mask over the air inlet.



Mark

 

[Okie]

At post 49,865 You need to clean the inlet sintered iron filter really good.
I've seen those filters get restricted and at first the engine starts starving for fuel in a loaded bar cut and then eventually cause lower speed erratic issues. You cannot usually see the restriction visually.

I use the Tillotson type carbs instead of the flatback but they have the same type sintered iron filter. They are a good filter is why they clog fast if the fuel is contaminated.
If I remove the sintered iron filter I keep and heads up and clean it the opposite direct of fuel flow with compressed air then re-install in the same orentation (direction) I've seen them get restricted fast if the fuel tank on a Mac is contaminated with molasses or the fine mold. The tank contamination get past the in tank filter and the sintered iron is finer and gets restricted. I've seen them start starving after consuming 1/2 tank of gas or less when the tank is contaminated.

Summary: Check the sintered iron filter and the gas tank for mold or old fuel molasses type sticky stuff. The new fuel and vib's causes it to get into the new gas.

I

 

[MacAttack]

At post 49,865 You need to clean the inlet sintered iron filter really good.
I've seen those filters get restricted and at first the engine starts starving for fuel in a loaded bar cut and then eventually cause lower speed erratic issues. You cannot usually see the restriction visually.

I use the Tillotson type carbs instead of the flatback but they have the same type sintered iron filter. They are a good filter is why they clog fast if the fuel is contaminated.
If I remove the sintered iron filter I keep and heads up and clean it the opposite direct of fuel flow with compressed air then re-install in the same orentation (direction) I've seen them get restricted fast if the fuel tank on a Mac is contaminated with molasses or the fine mold. The tank contamination get past the in tank filter and the sintered iron is finer and gets restricted. I've seen them start starving after consuming 1/2 tank of gas or less when the tank is contaminated.

Summary: Check the sintered iron filter and the gas tank for mold or old fuel molasses type sticky stuff. The new fuel and vib's causes it to get into the new gas.

I

Hi,

I completely cleaned out the tank before I assembled the saw. How do I clean the metal filter, it doesn't seem removable? Can I spray it with carb cleaner and blow compressed air through it?

Thanks!

 

[vinnywv]

They will pop out. The best fuel cleaner for me is called Goof off. That stuff.is incredible for carburetors. Everyone has a go to solution as im sure youll get here. Soak the carb diaphragms in it for about an hr and i swear they are like new and work perfectly fine. The 795 i recently got, the metering side crackled when moved..honest. i soaked it for 30 minutes and it was as pliable as new and works just fine. Try ot and youll swear by it. Im sure there are other items but that stuff works great for carburetors and carb parts.

 

[MacAttack]

I'll clean the filter in the flatback and see what happens, it's possible that it's plugged with varnish... thanks guys!