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.