Loss of power, lots of backfires, no start, help!

[alterednines]

All: took the Rally car to a cars and coffee today and got towed home. Here are the symptoms and yes we have searched CIS posts and Backfire yada yada.
Started fine this morning, ran well for about half the 15 mile trip then it started to backfire at 4k rpm and during decel. The idle dropped off to nothing so it was stalling at every light unless I heel/toed it to keep it running. Sat at the C&C for about 2 hrs, time to leave hard to start. It did eventually start and we were off. Made it 2/3 of the way home and it really started popping and spitting then without warning it spit and died. Started it up running rough, foot to the floor and little to no power, then it died.
What you need to know: 1976 911s with CIS, all CIS parts in place. Just had to remove, weld and replace the gas tank.
While sitting on the road waiting for our tow, I pulled the fuel filter, brown murky gas on the inlet, but clear on the outlet. Fuel pump runs while cranking but does not seem to with key on. Have not pulled plugs yet, just thought I would ask the experts where to look first. Thanks for the forthcoming input.

[kerthunk]

Fuel pump won't run unless the engine is spinning. Maybe a clogged fuel filter? I would pull the injectors and stick them in jars for a flow test. You can jump the fuel pump relay to get it to turn on while the key is in the "on" position. Then just stick your hand into the airbox and lift the arm a bit to get the injectors to squirt.

[Targalid]

Sounds like a plugged fuel filter to me too. What was the last thing you worked on? Fuel tank. Debris plugging the fuel filter and maybe the fuel lines to the filter. Hopefully nothing made it past the fuel filter into the fuel distributor. Probably not. Backfiring is a symptom of a really lean mixture. It all fits. I hope it is as simple as a plugged filter. Hope your air box made it through the backfires. Good luck!

[Joe Bob]

Fuel filter or the screen in the tank. Gauges for pressure check are mandantory for CIS.

[alterednines]

Thanks guys. The filter was really dirty on the inlet but clear on the outlet. Yes, the last thing we did was install the tank this morning after welding a bad spot yesterday. We had the tank out a number of times during the build of this car and cleaned it out pretty well. We were thinking about blowing air back thru the supply line. Can this damage the pump?
Thanks

[Joe Bob]

Disconnect the pump.........blow the lines out from the tank to where the pump connection is, then the lines to the filter.....disconnect that too. Have a fire watch....extinguiser ready.

[sailchef]

I shred the inside of the dizzy once. The shaft had developed a very slight wobble and the rotor ground the inside tabs to dust.

Symptoms came on kinda slow under normal driving, then just when I nailed it to pass another car it crapped out completely. I came to a rolling stop.

The car I was passing was an old lady in a Buick. True story.

Have you checked your dizzy lately?

[alterednines]

Yes, looked at the cap n rotor, looks normal. Hoping it is a fuel clog at this point. Will give the fuel pressure test after we clear the lines.
Keep you all posted.

[alterednines]

[RSTarga]

points are closed up