Not pulling fuel.

[TakemuraShuu]

Hello, I have a 1976 Sunny with an A14, Weber 38/38, and a new mechanical fuel pump, as well as a 1978 Silvia/200sx with an L20b, Weber 38/38, and new mechanical fuel pump. Both vehicles run briefly with ether.

 

Both vehicles suffer from the same issue: fuel pump only pulls fuel if the tank is full. I took some 5/16 fuel line and ran it from the tank straight to the filter then to the pump, skipping over the hard line just incase there's a blockage, and same issue. Both tanks are about at 70%.

 

I tried an electric fuel pump, mounted just under the tank on the Sunny, and same outcome, only pulls if the tank is at least 75%+. 

 

I'd really love to drive cars someday, however it's looking like I'd have to swap an efi engine in to ever achieve that. Any help would be greatly appreciated, thank you for reading.

[datzenmike]

I'm doubting a blockage that knows when the tank is below 3/4 so it shuts off fuel totally. How does a blockage do that? It can't.

It's also hard to believe two exact same fuel delivery problems that happen at 3/4 tank on two different cars.

 

 

I'll just take a guess here while I think about this some....

 

You have accidentally connected the fuel pump to the return line to the tank on both cars.  The return line does not need to reach the bottom of the tank, and only sticks down into the tank a few inches. If one fuel line is larger diameter than the other then that is the return, or usually is.

[TakemuraShuu]

23 minutes ago, datzenmike said:

I'm doubting a blockage that knows when the tank is below 3/4 so it shuts off fuel totally. How does a blockage do that? It can't.

It's also hard to believe two exact same fuel delivery problems that happen at 3/4 tank on two different cars.

 

 

I'll just take a guess here while I think about this some....

 

You have accidentally connected the fuel pump to the return line to the tank on both cars.  The return line does not need to reach the bottom of the tank, and only sticks down into the tank a few inches. If one fuel line is larger diameter than the other then that is the return, or usually is.

First off thank you so much for replying. I thought as much but can't find anything referencing which is which. This is how I have it set up on the Sunny. Larger tube is the return, and smaller tube is going to the pump, is this correct? And if so what else do you think it could possibly be?

Here's the image-

http://imgur.com/gallery/H8CpnrD

[datzenmike]

 

Is there a pipe coming out of the side of the tank. Perhaps on the side facing the back seat???

[TakemuraShuu]

On 11/27/2020 at 3:12 PM, datzenmike said:

 

Is there a pipe coming out of the side of the tank. Perhaps on the side facing the back seat??

Apologies for the very late reply, but no, there is only one other tube besides the fill tube and it's on top of the tank directly in the middle, not exactly sure what it's for or if it may be a reason for my current dilemma.

http://imgur.com/gallery/leyjid1

[datzenmike]

Well try reversing those two or try the 3rd one.

[banzai510(hainz)]

does one really need a return line?

 

Mike My 510 has a return line but when I got it it just has the fuel line and return was deleted. open under fender I think. works fine

 

[datzenmike]

Sure it wasn't the tank vent line? to the flow guide valve?

 

L20B cars and truck had return lines.

[banzai510(hainz)]

webers don't seem to need them. unless the fuel pump is different than a early 510 which you just route the line to carb and bam your done.  No return line

[datzenmike]

The return line is solely to circulate fresh cool fuel past the carburetor(s) that's all. Somewhere in the return line is a restriction or the pumped gas would just take the easy path back to the tank and wouldn't build any pressure. There is a pin hole in the return. It allows bubbles and over heated fuel to be pushed back into the tank. The return in no regulates fuel pressure that is done by the fuel pump.

 

Top is the return line. The hose on here goes down past the fuel pump to the return line under the car. The bottom hose is from the fuel pump. If you do have a return line there is no down side to having it. One advantage is that all the gas in the tank is repeatedly circulated (over time) and thus has to be filtered. A tank with a return line will stay cleaner.

[TakemuraShuu]

On 11/30/2020 at 7:11 PM, datzenmike said:

Well try reversing those two or try the 3rd one.

Tried that, no dice. This is very strange, are all carb cars like this? I don't understand why it won't pull the fuel unless the tank is near full. I honestly can't think of any reason.

[banzai510(hainz)]

take the gas cap off and see if it works then

[TakemuraShuu]

25 minutes ago, banzai510(hainz) said:

take the gas cap off and see if it works then

No change. I'm pretty sure that third one, the orange one, is fuel tank vent hose. I wish there was a diagram of the tank but can't seem to find one. I wonder why no one else has had an issue like this, I thought it'd be common. 😭

 

[datzenmike]

Try all three. One has to be the fuel line that goes down to the bottom of the tank. The return (if you have one) and the vent line stay near the top of the tank. There's no need to go any deeper.

 

Rap the tank maybe the fuel gauge sticks and is wrong and it's out of gas

[Crashtd420]

How about blowing into the tank though the tubes with some air.... if the tube is below the fuel level you should hear it blowing bulbs...

 

Its also a possibility that the pickup tube has holes in it...  

[TakemuraShuu]

6 minutes ago, Crashtd420 said:

How about blowing into the tank though the tubes with some air.... if the tube is below the fuel level you should hear it blowing bulbs...

 

Its also a possibility that the pickup tube has holes in it...  

Haha ironically I just did that to every hole, didn't really hear anything, just got a bit of a fuel smell. I think the only next step is to pull the tank at this point.

[banzai510(hainz)]

I forgot to mention its a long shot. really a BIG GUESS

maybe when iTANk is  full theres enough weight of the gas in the tank to go foward but the line has a hole and cant pull the gas up to the carb.

 

put a pusher fuel pump by the tank and then route it. (trouble shoot but a lot of work

 

 

I had a cracked fuel line right in front of the fuel pump and car still wouldn't start. . when I pulled of the pump then I notice a hairline crack in the rubber line

[datzenmike]

He said earlier he mounted an electric pump and a separate hose... no change.

[Crashtd420]

26 minutes ago, TakemuraShuu said:

Haha ironically I just did that to every hole, didn't really hear anything, just got a bit of a fuel smell. I think the only next step is to pull the tank at this point.

I'd definitely have a look at the pick up tube then....

[TakemuraShuu]

On 12/2/2020 at 4:16 PM, datzenmike said:

He said earlier he mounted an electric pump and a separate hose... no change.

So I removed the rear seat and like you said, there's an inlet with a hose. I believe this to be the fuel feed. I removed the existing hose (nothing came out oddly) and replaced it my new hose going to the pump and carb. No fuel coming out. Blew compressed air and still no change, and guesses?

[datzenmike]

I would imagine that the line part way down the side is the fuel outlet to the pump. A return (if it has one) and a tank vent line would need to be close to the top. 

 

Run a hose from the stock fuel line into a container of gas and start it up. It might take a while to draw fuel up and out of the container. If it runs, then the line and pump are confirmed ok.

[TakemuraShuu]

On 12/6/2020 at 12:27 PM, datzenmike said:

I would imagine that the line part way down the side is the fuel outlet to the pump. A return (if it has one) and a tank vent line would need to be close to the top. 

 

Run a hose from the stock fuel line into a container of gas and start it up. It might take a while to draw fuel up and out of the container. If it runs, then the line and pump are confirmed ok.

Thanks again for your help btw, I'd be completely lost if it wasn't for you. So I tried starting from a bottle of fuel and yes sir it ran from the bottle of fuel. So the culprit must be the tank! Question is how to get into the tank 🤔🤔

[datzenmike]

Sometimes all you need is someone looking over your shoulder.

 

To look into the tank .... through the sender. Drain after removal.  There's a ring collar that you can hammer with a punch to turn it. An O ring seals it, but if cleaned carefully can be reused or take it for a matching new one. Once the sender is out use a flashlight and take a look. The line inside, if you can see it? that goes almost to the bottom of the tank will be the outlet pipe. 

 

BUT FIRST try poking a wire up the fuel outlet line which I still think is the one part way down the side. Maybe blockage that can be dislodged.

[TakemuraShuu]

1 hour ago, datzenmike said:

Sometimes all you need is someone looking over your shoulder.

 

To look into the tank .... through the sender. Drain after removal.  There's a ring collar that you can hammer with a punch to turn it. An O ring seals it, but if cleaned carefully can be reused or take it for a matching new one. Once the sender is out use a flashlight and take a look. The line inside, if you can see it? that goes almost to the bottom of the tank will be the outlet pipe. 

 

BUT FIRST try poking a wire up the fuel outlet line which I still think is the one part way down the side. Maybe blockage that can be dislodged.

Tried poking a wire in, there's definitely a blockage somewhere because it just stops. Drained the fuel and took the tank out, removed the sender too look into the tank, can't really see anything. Blew 150psi into the fuel outlet, just builds pressure and shuts off. Is the only way to open the tank by cutting it open?

[datzenmike]

How far in?