What is this?

[Kalyn]

I have 1966 Mustang coupe, 200 CID, she had been sitting for 6 months. I had the carb rebuilt, and put in a new fuel pump and an in-line fuel filter. She drove like a dream for about 100 miles, then she started to lose power. If I pull over and let her sit for a minute, then she will go for a mile or two before losing power again.

I decided to replace the fuel filter with one of those glass ones and when I removed the old in-line filter, a bunch (about 1/2 cup) of very dark red fluid poured out of the fuel line. I put the fuel line into a bucket and started the car. I got about 4 cups of this nasty looking stuff, then clean gas started flowing. The red stuff looks like automatic transmission fluid. Wierd.

Now the fuel will run clear for anywhere from 20 to 100 miles then a few cups of the red stuff come out. I have to clean the filter so I can continue on my way.

Does anyone have any idea what this could be and/or how to fix it?

Thanks!

Kalyn