McCulloch Pro Mac 55: advice/knowledge needed

[Stihl dude]

I just bought a nice pro mac 55 and was wondering something

The saw currently has a Walbro SDC single jet carb (not sure if I am using the term correctly). It has an idle screw and a low jet screw. Seems to run nicely.

I have another SDC carb with double jets (idle L and H).

Should I swap the single jet out and put the double jet in ? Will it enhance the perfromance of the saw ?

Thx in advance

 

[Maintenance supervisor]

Ive never had problems with the "fixed jet " sdc carburetors.
They tend to get richer as they get closer to rebuild time.

 

[Stihl dude]

Ok that’s good news. Saw seems to run fine with the current carb.

Was wondering if performance would change with a double jet

 

[Jethro 2t sniffer]

Depends on the jet if you can sneak a little more out of that or not.

Often a little can be had but often nothing really and they are bang on tune wise.

Does it sound like it could be leaner?

 

[heimannm]

There are two basic "sizes" on the SDC carburetors.

Up to the SDC 16 and smaller are .625 venturi and .750 throttle bore.

The SDC18 and up are .750 venturi and .812 throttle bore.

My experience with the fixed H jet carburetors is they are wonderful for working, blubering if you just want to hear a saw rev up to screaming. If you are planning on using the saw for real work, leave the fixed jet carburetor as it.

In addition to the differences in venturi/bore size, there are internal and external idle and mixture adjustments (inside or outside the airbox) so you really need to know what you have and match it exactly with any replacement to retain the original adjustability.

Mark

 

[Stihl dude]

Depends on the jet if you can sneak a little more out of that or not.

Often a little can be had but often nothing really and they are bang on tune wise.

Does it sound like it could be leaner?

it does sound a little ''fat'' when I get on the trigger

 

[Jethro 2t sniffer]

it does sound a little ''fat'' when I get on the trigger

Mark pretty much nailed it really. The fixed jet do work well and once loaded up in the wood they clean up and cut well.

In saying that I have a 10-10S pretty sure same engine and to be honest that last little bit of fine tuning is quite important to get that special something out of it. Especially in smaller wood
It loves to be tuned really close to the edge. The 70s not so much. I have a few 70s both fixed and adjustable in Tillotson and walbro and yeah I'm really happy with them

Honestly for the sake of fun and learning I'd do it.

An sdc65 would be best as its setup for under the lid adjustments.

Otherwise you'll need to cut open the side and add the rubber bung thingy majiggy.

In saying that I run a sdc44 on my pm800 and it's ment to have a zama and the rubber majiggy doesn't work so I've just 100mph taped the hole and can turn the high with my fingers from under the lid.

Must rebuild that zama actually