Once per season since I put my car on the road in 1992, I have to dismantle my Edelbrock/Carter AFB and hose it out with Gunk carburetor cleaner to remove the grit-like material that seems to form in the float bowls and then passes into the delivery system. The symptoms are low and irregular idle, a severe flat spot above idle, and a difficulty in maintaining a steady driving speed. The first time I did this, I bought a rebuild kit to get fresh gaskets, etc. and also found that both float levels were off with one way out of spec. They've been fine since then, and I'm still using the same gaskets. After this cleansing, it runs like a top - easy starting, smooth idle and steady running.

Since last October, I've driven the car less than 100 miles, but I start it once per month and run it until the engine is fully warmed-up. I do this mostly to drive out moisture, keep the seals working, and charge the battery. I've found that this makes a huge difference when spring roles around.

I use an electric fuel pump with a high-quality fuel filter. I can't figure out what's causing this, or what it is. I say "grit-like", because it doesn't seem to be sand, although that's about the particle size, and I when I rub it between my fingers it will disintegrate.

I typically put less than 3,000 miles on the car each season, which is only about 7 tanks of fuel. I fill up at a name brand filling station, but seldom the same brand each time (I have no gasoline brand loyalty).

Any ideas at to what this mystery substance is, and/or what's causing it to form or appear in my carburetor? I'm beginning to suspect that the fuel line is deteriorating, but I've never heard of that happening.

For extra credit: what's the trick to re-assembling these carburetor bodies? I have to jiggle the upper body until it will fully lower onto the lower body. It feels like something is holding the two halves apart on one point, but I can't figure out what that point is.