I am a big fan of supplemental fuel filtering. It is necessary if you want modern day reliability from a machine with a primitive fuel screening system.
Properly installed supplemental filtering used in conjunction with good fuel line will eliminate the problems that flow into your carburator with the gas, plugging orfices and propping open needle valves or at the very least, causing poor starting and engine performance.
I installed the first inline fuel filter on my dad's cub in the late '70's. That filter lasted almost 25 years with only sediment bowl service, the carburator provided outstanding performance the for two and a half decades. Ten years ago when I inherited the tractor, it was serviced and that filter was replaced.
A couple of years ago, I again changed the filter, this time I opted for a clear glass "racing" filter. And just as reported in previous posts, I also thought it was an oddity not to see fuel in the sight glass yet the gas continued to flow at an appropriate rate.
I didn't dwell on it and the tractor never missed a beat regardless of how little fuel was visible in the sight glass.
In a matter of days the inside of the filter was looking terrible but at least it was stopping the crud before it got to the carb.
Upon close inspection of the fuel tank, I could see why the filter was looking bad, the inside of the tank looked horrible. And it still does.
I decided I needed an additional layer of filter protection so I installed a replaceable in-tank filter cartridge.
This filtering system has worked so well for me the clear inline filter still looks like new inside after almost 2 years of service.
I'm actually considering abandoning the external inline filter and bringing the copper fuel line up to code.
I searched the forum to see if anyone had done this before and found metallic sock like mesh filters have been installed but look to be permanently attached.
I chose to use a disposable cartridge because with the condition of my tank, I knew it would eventually plug up with the crap I saw collecting inside my clear inline filter.
This is a real easy modification and the best part as aforementioned, it is replaceable in about 30 seconds as often as necessary for about 3 bucks.
Obtain a one inch long piece of stiff plastic fuel line with an outside diameter of 1/4". This plastic line is usually clear and used on 2 cycle small power equipment. This piece will be inserted into the inlet of the sediment bowl to create a short standpipe inside the fuel tank.
(The inside of the sediment bowl tube is exactly the same diameter as the hole in the filter so if the fuel line you will be using fits snugly in the filter it will fit snugly inside the sediment bowl tube.)
If your sediment bowl is not IHC, I can't assure you it will be the same size.
Next buy a Fram CG 3389 paper element gas filter utilized back in the Quadrajet era from any auto parts jobber. Pull out the rubber end piece seal incorporating the check valve and spring. Cut the the end of the rubber cage off and discard it along with the valve and spring. Replace the rubber seal into the end of the filter. (This rubber insert is good for use in all modern fuels.)
The easiest way to install the standpipe is to drain the tank and remove the sediment bowl, but if you have patience, you can run it down a piece of stiff wire from the tank filler neck followed by a handful of 1/4" deep sockets. Press the tube down into the sediment bowl neck with the stacked sockets before extracting the guide wire. Retrieve the sockets with a magnet.
Reinstall the sediment bowl if it was removed to insert the plastic tube.
Next, obtain a long reach set of needle nose pliers, grasp the closed pressed metal end cap of the filter cartridge and lower it into the tank, pressing the opening with the rubber seal over the end of the standpipe protruding from the sediment bowl.
Have a set of mechanical fingers handy because you'll probably need to retrieve the filter at least once before successfully pressing it over the pipe. You may need a helper to hold the light if you don't have a hat or helmet light. You may find an easier way to install the filter by means of experimentation but I can usually stick them on the first or second try with the pliers.
Two paragraphs of caution....
Primarily remember if any fuel residue remains in the tank, you will be working over fumes so procede with and exercise extreme due caution.
Secondly, pre clean anything you dip in the tank. Your pliers, sockets, retriever, or any other device you recruit to press the filter onto the pipe needs to be spotless. Even though the filter will catch it, try not to add to the existing problem.
I recall recently reading a post by Bus Driver about bringing home unused surgical supplies from the doctors office for later use in the shop. Cub fuel systems require surgical suite like cleanliness all the way from the tank to the carburator if you expect trouble free operation and good performance. Use only clean tools when working inside any fuel system, gas or Diesel alike.
In-tank or inline fuel filters will not stop crap shedding from the fuel line so if you continue to be plagued with carb blockage, I would suggest replacement of the fuel line as soon as possible.
I will assure you that you will never see anything collect in the sediment bowl again as long as the filter remains in place.
I replace my in-tank filters once per year.
Clean fuel causes no problems.