McCulloch Pro Mac 850 Questions

[m21bmr]

McCulloch Pro Mac 850 Carb Question

I recently purchased a McCulloch Pro Mac 850 from Craigslist, and was trying to check it out and get it running well.

It has good compression. About 170 psi on my compression tester, and has spark as well. It ran to some degree when I got it home, but wouldn't stay idling, and seemed very rich when it revved up. I adjusted the carb needles a little, and now can't get it to start. It will hit a few times, but not stay running. It has a Zama carburetor. Does anyone know how many turns off seated the "base" setting for the carb should be on this saw? About 1 1/2 turns?

Here are a few pictures of the saw.

 

[Tzed250]

.


Hmmmm... M21BMR...I've got one of those...


.

 

[Rustynutz]

Its probly due for a carb kit! and plugs points etc etc
if it runs at high speed ok but not idle that's blocked L jet and needs a clean!
you can remove the jet, WD40 with the red tube, put that in and squirt you should see it come out both the idle holes (take the filter out!) to see down.
I suspect looking at it! a brittle diaphragm? faulty metering needle? the usual.
H L jets 1 1/4 turns on each it should start and run, you can increase the throttle stop screw a bit wile your setting it up.



nice looking saws and worth reconditioning, I had a brand new one when they first come out! great tool in its day, been a mac man ever since.

 

[Roanoker494]

Nice looking saw you got there, I would not mind finding a 850 myself.

+1 on the carb rebuild, maybe a fuel line and filter while you are in that area.

 

[RandyMac]

850s look funny with a short bar.

 

[m21bmr]

After I posted the original message I went out and tinkered around with it some more. I did get it to run and idle. I suspect that the carb could use a rebuild kit.

I've never run a saw anywhere near this displacement (The largest other saw I own currently is the 36cc Echo). This McCulloch seems like a beast. I bought my Echo used and tested the compression on it for comparison. I got about 140 psi on the Echo. Is the 170 reading that I got on the 850 typical for this model saw? Thanks.

 

[m21bmr]

.


Hmmmm... M21BMR...I've got one of those...


.

I've got a 1991 Lawnboy M21BMR that I've owned since it was new. Good mower.

 

[rwoods]

So you are the one that snagged it. Great buy. Put a longer bar on it and it will go for 8 to 10 times what you paid for it on Ebay.

From what I have read on this site the compression reading is fairly typical for this saw. Great saw. Rebuild the carb and don't look back. Ron

 

[Rustynutz]

haha
yes that's definitely a joke size bar for that saw!!
mine ran a 24" no problem, and looks better for it
you can get some heat shrink for the handle, looks good and reasonably hard wearing