Need help tuning McCulloch MAC 1-10 Bullfrog Carb, turns over but won't stay running...

[Jay Jones]

Hey every one! First post on this forum, stumbled upon the site looking for some insight on how to tune the Mac bullfrog carb.

Inherited this McCulloch Mac 110 from a friend of mine who passed away. She sat for about 10 to 15 years in storage. We had tried years ago to get her running only to find out the parts are hard to find. So this mission is being set fourth in his honor.

I recently disassembled the whole thing and cleaned her up and took apart the carburetor. Diaphragm was stiff and rigid I found a new one on eBay for about 25 bucks shipping included. Reinstalled it, put it all back together. She will turn over and run a little bit, (some times full RPMs then kaput) but I'm not sure how to set the high, low and idle screws. Also she leaks a little bit of fuel from the primer side and the fuel metering needle.

I acquired the shop manual (scanned pdf), but some of the pictures are hard to make out. It looks like the single needle version.

Wondering if this was an adjustment that can be done, or if I need to get new O-rings for the primer. I also saw that there is a duckbill check valve that commonly clogs up. Any help suggestions, Insight on tuning this carb would be greatly appreciated. I would love to get this puppy running to go cut down some wood 4 a bonfire down by the river!

Thanks in advance for any advice!!

Jay

 

[Jay Jones]

These pics are all PRE cleaning, sanded smooth that top & bottom (on the tank assembly) carb mount just a hair. I also reused the intake gaskets they were in pretty good shape.

Also, don't know how important it is but the 2 bolts that held on the carb had 2 washers on them. One was metal, the other was some sort of fiber glass. I broke both the fiber glass ones. How important are those fiber ones? The torque specs say 60 lbs!! Could I just use more metal ones? or just delete em??

Side note, has any one tried to port and polish these carbs and tank assembly intake? the opening in the cylinder head is WAY bigger then the tiny opening in the carb!!

Thanks again for any advise!

 

[Chainsaw Jim]

I'd track down a set of crankcase seals, and a carb upgrade would be a good idea to complete the project. Most parts on the 10 series are interchangeable.

 

[heimannm]

Seals are a good suggestion, it is possible to change out the flywheel side fairly easily but changing the PTO side is most easily accomplished by splitting the crankcase. Not really a big job but does take a bit of time and clean up.

Updating the carburetor is not really an option without changing the tank bottom/air box; in fact McCulloch offered a retrofit kit to achieve that task to provide the additional clearance needed for the taller cube style carburetor.



Your carburetor is indeed the single needle type.



The low mix screw (red circle) should be 2 to 2-1/2 turns open from lighted seated, hold your finger on the butterfly to determine when the needle is seated.

The idle speed screw (green square) is used to control the idle speed, some have a low speed governor as well.

The high speed/mix screw (blue arrow) controls the full open position of the throttle (+/- 7 degrees of horizontal won't affect the throttle opening) but controls how far the needle is "extracted" more extraction for a richer "H", less extraction for a leaner "H".

Easy as that.

The duckbill valves are NLA but you can get by drilling out the passage to 5/32" and using the red Homelite duckbill.





Mark

 

[Jay Jones]

Seals are a good suggestion, it is possible to change out the flywheel side fairly easily but changing the PTO side is most easily accomplished by splitting the crankcase. Not really a big job but does take a bit of time and clean up.

Updating the carburetor is not really an option without changing the tank bottom/air box; in fact McCulloch offered a retrofit kit to achieve that task to provide the additional clearance needed for the taller cube style carburetor.

View attachment 699359

Your carburetor is indeed the single needle type.

View attachment 699363

The low mix screw (red circle) should be 2 to 2-1/2 turns open from lighted seated, hold your finger on the butterfly to determine when the needle is seated.

The idle speed screw (green square) is used to control the idle speed, some have a low speed governor as well.

The high speed/mix screw (blue arrow) controls the full open position of the throttle (+/- 7 degrees of horizontal won't affect the throttle opening) but controls how far the needle is "extracted" more extraction for a richer "H", less extraction for a leaner "H".

Easy as that.

The duckbill valves are NLA but you can get by drilling out the passage to 5/32" and using the red Homelite duckbill.

View attachment 699364
View attachment 699365
View attachment 699366

Mark

Do you mean these crank seals?

I also think its 100% the duckbill I took a video as I was disassembling and I though it was just gunk in the line HAHA. Turns the duckbill was toast. Do you happen to have the part# for this replacement?? I'm guessing this is internet order only. Would Home depot or Lowes have this? Maybe advance or Pep boys??

Thanks again Mark this is going to be a big help!!! I can smell the saw dust already.

 

[heimannm]

Most shops that work on older saws would have the duck bill valves, or would know how to order them. The Homelite PN is 69541, Oregon PN 07-004, Stens PN 610345.

The flywheel side seal is either 1.375" O.D. or 1.5" O.D. depending on which bearing the saw has. One bearing has a wider outer race and the seal presses in, the other bearing is narrow and the seal presses in the same bore of the crankshaft.

The PTO side seal has a much smaller O.D. .625" shaft x .875" O.D.

Mark

 

[matt_lamb_160]

Hi all, I am currently trying to repair a bullfrog carb off of a 3-10E which has clearly been apart before. The duckbill is eaten away. There are no check balls anywhere in the carb, I have noticed others saying be careful not to lose them. So should there be a check ball and if so, what size are they and where should it go?

 

[heimannm]

There were at least 5 different versions of the bullfrog, you need to look through the IPL's and identify your exact model as not all used check balls in the primer circuit.

Somewhere there is a thread on the 10 Series carburetors that details one workaround for the OEM duckbill valve.

Mark

 

[matt_lamb_160]

Thanks for the reply Mark. I managed to find a workshop manual on here:

https://www.arboristsite.com/community/threads/mcculloch-manuals-new-and-improved.247377/

It looks like mine is a type 5. I haven't had much time to look at the documentation yet, but it appears that I am missing the check ball and seat and the valve/o-ring used to locate them.