View attachment 502061 Yes, I just love their attention to making the saw as quiet as possible - I can see this from the ear defenders in the previous post.....
You will probably find when you put it in the wood that you have the L screw too far out at your 1 1/2 turns.
If either the H or L screw is too far out on most of them old 140 series saws they will sound real good unloaded but when in the cut it will eventually start losing power. Adjust all for the 4 cycling. blubbler when removed from the cut and before going into the cut. Keep the jets in as far as possible to keep the saw rich.
Here is a link for some HL carb info. If the link don't work do a for Tillotson HL series carb service manual download.
http://www.eccarburetors.com/pdf/HL service manual.pdf
Note the position of the sandwiched gaskets and diaphragms and also note in the service manual how to test the pump pressure as you are cranking the saw. (I've made the 1/4 28 adapter for testing such using a 1/4 28 stud and nut with the small hole drilled in the stud)
Also if the gas tank has the aluminum brown mold from old gas the fine mold will get past the in tank filter and constantly restrict (clog up) the sintered iron filter in the carb and the saw will starve for gas under load. You cannot see it in the sintered filter but will find it if you take a air gun to the filter while using a white paper towel behind.
Also be careful cleaning the carb and don't use high pressure air or you will blow out some of the welch plugs or make them leak and you won't notice such until your ears and finger are bleeding again from cranking the saw.
I've bought tillotson HL series carbs new and used from flea bay the D and E series. You have to watch out the the letter series like your A it usually relates to the choke or throttle linkages. For example the HL63D does have a choke butterfly in the carb and the 63E has a spring loaded choke butterfly and the E can be used in place of the D but not vice versa. I did not find a pic or any info about the A series. Their was a good site called Chainsawr.com awhile back that had good used parts and McCulloch interchange tech info info but I can seem to find it today.
I've never worked on a 1-40, just 1-43, 1-53, etc but it appears that your choke lever is on the left side and has the plastic blocker inside that blocks the carb throat like the like the 63 D carb.
More pics of the throat end and top and bottom of the cab would help ID and a top view pic of the carb on the saw with the breather removed.
I have about 6 good running 1-40 and 150 series of the old back breaker McCullochs (that I use on the big logs when the trees are already down, just lay the big saw on the log and pull the trigger) and about 3 spare carbs. I have a old McCulloch flatback type carb that I removed from one 1-40 or 1-50 series and replaced it with a Tillotson carb. the kit was expensive for the old McCulloc. flatback and not readily available was why I converted. (McCulloch did the same conversion as standard OEM when they went to Tillotson.)
The low speed jet if out too far will cause the H speed to have good load-up problems even thou the saw idles good. Keep all jets in as far as possible and still get a good idle, but 4 cycle when coming out of the cut as the saw is unloaded. Sometimes a 1/8 turn of a jet will make a big difference on some of the old Mac's. Keep the air filter clean.