Chris-PA
Where the Wild Things Are
My McCulloch Silver Eagle 3420 (basically a PM605) is running well, but I've had a hard time tuning it. To get it tuned the L needle needs to be at 1/8 turn open. It's runs mostly OK like that, but it has an additional symptom in that it takes a long time to idle down after you release the throttle - maybe 2 or 3 seconds. This is not a big deal and it's been working fine, but it bugs me because I know it's not right. It means the basic mixture at idle is too rich, beyond what can be adjusted out of the carb (needles and seats appear fine), and probably the H mixture is better so it runs faster for a moment after you drop the throttle.
This was my Dad's saw, and at some point he replaced the carb, and I don't know where he got it. I suspect the original was a Zama C2S, but I don't know. This one is a Walbro HBD-6B.
I recently bought a used carb and new needles from EvilBay, and the carb that came with it is also an HDB, but the venturi is marked 48. Mine is marked 40. It's also an older casting and it's much nicer made and finished. And it's missing the inlet fitting, which I made a separate thread about. It has HBD cast in it but no other identifying marks that I can see.
I do not know how to associate the venturi sizes with the model, nor what is appropriate for the saw. I got to thinking last night that maybe this is the problem - if the venturi is too small for the displacement, even at idle it will be drawing more air than the carb was set up for - probably activating more of the main circuit along with the idle nozzles.
So does anyone know what venturi size a 3420/PM605 should have, or how to connect venturi sizes with HDB model numbers?
This was my Dad's saw, and at some point he replaced the carb, and I don't know where he got it. I suspect the original was a Zama C2S, but I don't know. This one is a Walbro HBD-6B.
I recently bought a used carb and new needles from EvilBay, and the carb that came with it is also an HDB, but the venturi is marked 48. Mine is marked 40. It's also an older casting and it's much nicer made and finished. And it's missing the inlet fitting, which I made a separate thread about. It has HBD cast in it but no other identifying marks that I can see.
I do not know how to associate the venturi sizes with the model, nor what is appropriate for the saw. I got to thinking last night that maybe this is the problem - if the venturi is too small for the displacement, even at idle it will be drawing more air than the carb was set up for - probably activating more of the main circuit along with the idle nozzles.
So does anyone know what venturi size a 3420/PM605 should have, or how to connect venturi sizes with HDB model numbers?
