When fuel lines get old (99 U320), is the symptom usually "sucking air", or is a stopped up pre-filter common? Not sure if my Winn stainless steel screen is catching deteriorated line or if I got trashy fuel. Didn't think to feel of it when I had to clean it out on the side of the road. Small black stuff. All I've seen mentioned is "sucking air".
Had the tank cleaned about 2 years ago.
Sure sounds like fuel line. Another tank of fuel will tell you
Could be algae. Try fuel treatment for algae just so you eliminate this possibility.
Algae is black and is soft. Fuel line gets cracks that let air in but usually no black pieces of rubber. You could always Vicegrip it at the tank and use a MityVac at the other end to check for leaks.
Check your filter again.
Pierce
Sure sounds like bad fuel to me.
Some thing else to consider: Were you driving over rough roads with some ups and downs. Consider the possibility of sloshing around in the tank and dislodging sediment. I've been there. Replaced primary and secondary filters and all has been well since. I also added a biocide just to cover that aspect. This event caused me to put a vacuum gauge between the primary and secondary filters to monitor the primary filter to see if I could detect a plugging of the primary filter. Normal suction vacuum on the primary filter at idle speed has been running about 2.5 inches of vacuum. My plan is to monitor that and watch for an increase in suction vacuum which would indicate a plugging condition. Have a great day. ---- Fritz
The Winn is a constant problem when older. Amplified by cracked fuel lines. Replace both
I vote against fuel line particles blocking your filter. Progressively difficult starting due to air infiltration is the typical symptom of fuel line failure.
Why spend a lot of $$ if you don't need to? Buy one of these, clamp the fuel line at the tank and use this tool at the engine and you can see if the fuel line is the problem in a few minutes. https://www.harborfreight.com/mityvac-vacuum-pump-39522.html Can't go wrong for $42.
If you do install a new fuel line, cover it with this type of expandable sleeve. For electrical cables or fuel lines, this makes installation 10X easier as it's super slippery and slides past almost anything. Plus, the rodents don't like it.
Amazon.com: Electriduct 1/2" PET Expandable Braid Sleeving Flexible Wire... (https://www.amazon.com/PET-Expandable-Braided-Sleeving-Color/dp/B00BM80FKY). It should fit tightly so buy the same size as the O.D. of the hose.
Pierce
I used this to make the fuel line pull easy. Got the idea off of someones post.
https://www.homedepot.com/p/Klein-Tools-32-oz-Premium-Synthetic-Clear-Lubricant-51028/100660159
If the "clear" plastic holder is full if black stuff it is algae. If it is clogged then another tank of fuel will not fix it. Loosen the thumb screw on the top fitting. Put a small bucket under the strainer to catch any fuel spill. Pull the top part off watch for any loose orings. Hook the top part on something or use a bungee cord to keep it up. Pull the strainer up from the bottom part. Drain any fuel out. Get a bucket of hot soapy water an clean it out, the black stuff will swish out pretty easily. Once it is clean rinse well and use some alcohol as a final inside rinse. Reassemble in he reverse order. The should be an oring on the top and bottom tubes of the plastic holder. Carefully push it into the bottom holder and position the top holder push them together. This is the part where rough handling gan break the plastic part. Get the thumb screw started and screw it in all the way. A pliers might be needed.
Use the air/purge/primer button to purge air and fill it with fuel. Do it three times. The start the engine and runit on high idle for 2 or 3 minutes. If it doesn't start or quits after a short bit reprime and try again.