From a Mac service manual for the HL tillotson carb.
If you look closely you can see that the bronze filter has a coarse side and a fine side. (as you noted)
Fuel should enter first on the coarse side. Did not see this actually noted anywhere but common sense to use the coarse side first. (also note the below cleaning procedure for the bronze filter from service manual as a hint)
From MAC service manual:
Blow air through the sintered bronze filter from the fine side towards the coarse side for a through cleaning.
Also when using low pressure air nozzle keep the end of the air nozzle at least one inch from the carb to prevent blowing out or loosening the welch plugs.
From experience:
I've seen a fine mold grow inside the gas tanks on them old Mac's, hard to see but you can see it on a cloth as fine gray or black color.
If not removed the sintered bronze filter will clog very fast as the saw is being operated due to vibration and the saw will starve for High speed fuel.
When I see one really bad inside the tank I take off the bar, put little bit of mixed gas or even water in the gas tank and piece of old porch chain or equivalent, wrap the block in a piece of old carpet or padding and strap the block to a elevated tractor tire or a lawn tractor tire and slowly rotate and let the chain do the cleaning of the tank. You can get an idea of your cleaning by pour the contents through a paper towel.
The fine mold stuff that I mention will get through the in tank filter and clog the bronze filter.
This method will also get the loose magnesium powder particles out of the tank.
I store my Mac's tanks with fuel mix to slow the growth of mold and magnesium powder from forming. A dry tank speed the growth process.
Keep a close heads up notice when re-installing, bolting down the carb to the saw block. Make sure all is aligned properly because you can break a ear off the carb. One of the carb spacers has a raised ridge that must fit flat to the intake.
Here is a link to a post on this site about some of the 1-40 series carbs. Has some good tips.
This is page 2 link. see pg 1 also.
https://www.arboristsite.com/commun...1-40-tillotson-hl-63a-questions.296568/page-2
You can go the Tillotson.com site and see exploded views and some service info tips for the
HL series carbs.
