Mac 120

[Aragorn]

I have a Mac 120 I'm trying to bring back to life. It died years ago when ethanol came on the scene. I got another saw, but would like to dedicate that, with 3/8 drive and automatic oiler, to a Simpson capstan winch.
I soaked and rebuilt the Walbro carb on the 120. In the process I raised the float needle tab slightly. On reassembly, it would fire then die with abundant fuel emitting from exhaust on subsequent attempts to restart.
I went back in and lowered the tab. Now it starts and idles well but will not accept throttle, with little or no response to hi speed needle adjustment. Did I flatten the tab too much?
I know....I should toss it and get a real saw. I just don't like being beaten by an inanimate object.

 

[backhoelover]

what carb is on that unit i seen you the manual to check fulcrum lever height.
?

 

[Aragorn]

That would be excellent!
It is a Walbro D1 MDC.

 

[Little Al]

Check the needle lever height, the lever should just touch a straight edge placed across the carb body the 'L' & "H" mixture screws initial adjustment is 5/8 turn open from lightly seated The 'L' screw setting will affect the saws ability to accelerate if it hesitates open 'L ' slightly when adjusting 'L' rest idle screw to suit.

 

[Aragorn]

Check the needle lever height, the lever should just touch a straight edge placed across the carb body the 'L' & "H" mixture screws initial adjustment is 5/8 turn open from lightly seated The 'L' screw setting will affect the saws ability to accelerate if it hesitates open 'L ' slightly when adjusting 'L' rest idle screw to suit.

[/QUOTE]

Excellent, thanks! Can you clarify what you mean by "...when adjusting 'L' rest idle screw to suit"? What is meant by "rest"? Presuming this means "adjust" the idle screw which is the spring loaded screw used to set the trigger during startup?

 

[Little Al]

Excellent, thanks! Can you clarify what you mean by "...when adjusting 'L' rest idle screw to suit"? What is meant by "rest"? Presuming this means "adjust" the idle screw which is the spring loaded screw used to set the trigger during startup?[/QUOTE]
Sorry 'podgy' fingers,& old age, should read Reset idle, the Idle screw is the screw on the carb that pushes on to part of the throttle spindle When you release the trigger the saw when adjusted goes to idling Screwing in the increases the idle revs screwing out has the opposite effect The bit I think you were referring to is the fast idle latch, the idle screw is to set to keep the saw idling/running when you are not touching the trigger.

 

[Aragorn]

Excellent, thanks! Can you clarify what you mean by "...when adjusting 'L' rest idle screw to suit"? What is meant by "rest"? Presuming this means "adjust" the idle screw which is the spring loaded screw used to set the trigger during startup?

Sorry 'podgy' fingers,& old age, should read Reset idle, the Idle screw is the screw on the carb that pushes on to part of the throttle spindle When you release the trigger the saw when adjusted goes to idling Screwing in the increases the idle revs screwing out has the opposite effect The bit I think you were referring to is the fast idle latch, the idle screw is to set to keep the saw idling/running when you are not touching the trigger.[/QUOTE]

I'm not with the saw now, but I gather the idle screw is accessed thru the same hole in the top cover as the L/Hi screws, and applies pressure against the tab into which the "throttle spindle" is hooked? Also, how deeply should the "fast idle latch" spring loaded screw be seated? Since it is spring loaded I presume it is not to be bottomed out but just so much as to catch the tab for the throttle plate when depressed as the throttle trigger is held open?

I'll be doing my third tear down tonight. At least the "practice" has provided me with the ability to tear it down in 15 minutes or so

 

[Little Al]

Just screw in enough for the Fast Idle latch to make contact & stay in place

 

[Aragorn]

Great, thanks. I'll post a victory reply in the event I'm successful..........

 

[Aragorn]

The good news...disassembly only took 13 minutes. Adjusted lever to level with carb rim. Lost the idle latch spring during disassembly and never did find it even with smooth concrete floor. Reassembled and ready to try out in under 1hr, including spring search.
Bad news...it barks during choke, and runs a couple seconds and dies unchoked. Re choke, bark, unchoke, runs 2 seconds and dies. Tried opening L more than 5/8 in 1/4 increments. No change. H set at 1 1/2 out.
Will this saw start without idle latch set? Is H setting critical to start?
Running out of patience.
Also, never did find an idle screw.