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Re: 1975 Spider only runs with choke

Posted: Sat Jul 27, 2019 9:43 pm
by kendall
The saga continues.

So today I learned that the fuel gauge was not reading correctly. Ever since I've had the car it has shown that the tank was full, and I really have not run it much.

I go to try to drive the car around the block to my garage to do some work this morning and it doesn't run. I test the fuel pump directly to the battery and I can hear and feel it running. I was told that it was changed and it does look new. It seems to be working fine. Next I pulled the fuel sending unit and take a look in the gas tank. It was nearly empty. So I went to the gas station down the street and get some gas. It runs enough to get it to my garage but then it dies and I can't get it to idle again.

I changed the fuel filter before the fuel pump to a clear one, as I suspected that lots of dirt and debris from the bottom of the tank may have clogged it. The new filter nearly instantly got completely clogged with dirt as I tried to start the car. I changed it to a second one and it is only showing a small amount of discoloration so far. I still can't get enough fuel up to the carb bowl for it to idle.

Thank you for reading. Here are my questions:

How likely is it that the fuel pump itself is clogged? Wouldn't the fuel filter protect it? Can it be backflushed to clean it?

Can the hard fuel lines that lead from the pump get clogged as well? Can they be cleared out, possibly with compressed air?

Does the fuel system need to be primed in some way to get it up to the carb? If I filled the lines up from where they feed to the carb will that help it flow?

How long should the fuel pump need to run to get enough fuel up to the carb if the system were drained? It probably ran for 5 to 10 minutes at least when I was trouble shooting.

Is it really an issue to use a clear plastic fuel filter? I understand that metal or glass would be more hardy, but the plastic must be fine to some degree.

Thank you all very much for your help. I'll get this damn thing running if I can help it.

Re: 1975 Spider only runs with choke

Posted: Sat Jul 27, 2019 11:22 pm
by 18Fiatsandcounting
Hard to say, as I think the answer to all your questions is, "Possibly".

Here's what I would do, and this goes easier with a helper. With the engine cold, disconnect the fuel line going into the carburetor and put the line into a large, clean glass container of some sort. Caution when working with gasoline of course. Have your helper turn the ignition key to "run" and see how much fuel is coming out of the line into the container, and how clean it is. If you get about a cup of gas after a few seconds, and the gas looks pretty clean with no particulates floating around, your fuel pump and lines are probably OK (and you can dump the gas back into the tank). If the gas comes out of the line in a sputtering fashion, has crud in it or is tan or yellowish, you still have residue in your fuel lines.

If the gas comes out clean and steady, the problem is likely with blockages in your carburetor. I forget: Has the carburetor been taken apart and really cleaned? If not, it's probably time. Also, it might be a good idea to install an extra inline fuel filter right before the carburetor. And, as far as I know, there's nothing wrong with the see-through plastic filters that you can buy for a buck or two. These wouldn't be sufficient for fuel injection, but as extra precaution for a carbureted car, should be fine.


Re: 1975 Spider only runs with choke

Posted: Sat Jul 27, 2019 11:50 pm
by kendall
Thanks Bryan.

So I already have a clear filter before the carb and it is showing basically no flow. It had maybe a teaspoon more gas in it after I had let the pump run for a while. You can see the fluid pulsing with the action of the pump, but no new fuel is coming up. I guess I'll have to work my way back towards the pump to find where the blockage is.

I do know that the pump was working good before, as I did exactly what you described and got plenty of gas pulled up into a container off the carb.

Re: 1975 Spider only runs with choke

Posted: Sun Jul 28, 2019 12:13 am
by 18Fiatsandcounting
Yes, I agree. How about disconnecting the line at the output of the fuel pump, turning the ignition on, and seeing if you have fuel coming out of the pump? If not, the problem would either be the pump, the filter before it, the line from there back to the tank, or the fuel pickup in the tank. Speaking of which, I recall there is a metal screen on the end of the fuel pickup. Does that look OK in terms of not being plugged? One other thought: If there are any rubber fuel lines between the pump and the tank, I'd replace those. If they have developed an air leak, even minor, the fuel pump is just pumping air through the leak, and it could describe some of the symptoms you're seeing.

Apologies if you've already covered this earlier in the post.


Re: 1975 Spider only runs with choke

Posted: Sun Jul 28, 2019 1:36 am
by davedecker4
The answer to most of your questions is, yes. The only thing is it shouldn't take 5 or 10min of pump running to get fuel to the carb.
One thing that can affect it is if the float is adjusted down or needle sticking in the carb so it doesn't keep enough fuel in the carb to run. You can remove the aircleaner lid and pour a couple tablespoon of fuel in before running the pump and trying to start to help prime the system. (Do Not do this while starting! You can burn yourself if it backfires).
It sounds more like you have tank issues tho (although it could be both). Especially since you plugged the filter so quick. You can blow out the lines with air, disconnect both ends first and point it where it wont cause a problem. After that, easiest thing would be get a can of fresh gas and a piece of hose long enough to drop into the can and connect the other end to the electric pump. If this comes out clean and you can run the car well off it while sitting, the problem is in the tank. If it doesn't, you have a problem downstream (possibly in addition to). If it runs fine that way, see if your local radiator shop will boil out your tank for you. There are home cleaner methods but they're a hassle and typically don't work quite as well. Worst case, you can buy a new tank.