Help--fuel system problem

[MS Fowler]

My friend's 300CD starts and runs great, EXCEPT....
Recently, on a few trips there is a great loss of power, well when you have a 5 cyl non turbo, ANY loss of power seems great. But this loss is significant with a top speed of maybe 20 30mph.
We thought that maybe the tanks screen was plugged. So after draining the fuel ( very dark), he pulled the screen, and it was clean. When he had the power loss there were a few specks in the priimary filter. But the tank looks clean.
Right now the plan is to blow out fuel supply and return lines to make sure there is no debris, and reassemble. Replace both filters, and see how it runs.

Have we overlooked anything?
What else could casue the problem?

[Palangi]

Air leaks?

Cracked pre-filter? Old fuel hose on either side of the prefilter?

Leaking primer pump? Leak at the main filter?

Snug up the hollow bolts on the clear fuel lines.

Could those specks have been algea?Just in case,maybe you should dump some algeaside in you'r tank to kill any that might still be in there.Never run into algea in my fuel myself,but I've heard a fair amount about it over the years.

[MS Fowler]

He already dumped a lot of algaecide in the tank. We had expected that their little dead bodies had clogged the screen. After draining the tank, now I think the dark color of the fuel was their little dead bodies liquified. Perhaps its time to replace the spin on filter, again.
It runs so well when it runs that I am thinking it must be fuel related. Am I overlooking something?

[t walgamuth]

do change the main fileter though. that will prob do it. sounds like you have done everything else though. run the fungicide a few more times to be sure you got it all. unless you had the tank boiled out. which in my op is not nec.

tom w

[TwitchKitty]

Look for a BoneheadDoctor thread on a fuel system problem. Crankcase breather problems resulted in positive pressure behind the fuel shutoff diaphram and shutdown the fuel supply at cruising speeds. I doubt this is a common problem but the thread is worth reading.

More obvious causes are also discussed in that thread.

Primary filter costs about $2.00, 5 minutes to swap, sometimes not easy to see how clogged it is. I went through several soon after starting to burn UCO (used cooking oil) in my '80 300TD.

[MS Fowler]

Well, today, we blew out the fuel lines, changed both filers and put in 5 gallons of fresh fuel. After priming the fuel system, it started within about 2 seconds of cranking. Started and ran fine. He went for a half hour drive and got home OK, so maybe its fixed.

Also make sure that the fuel tank vent is not plugged.