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Purge new fuel system?
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Ulu
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PostPosted: Wed Dec 01, 2021 12:54 pm    Post subject: Purge new fuel system? Reply with quote

I have a dry fuel tank, dry fuel line, new hoses, dry fuel pump and a dry carburetor.

I have a vented fuel tank and the carburetor is probably vented as well, because there is no charcoal canister on this car. (I want one but that is another subject.)

I’m going to start this rig up for the first time with the new fuel system. The engine runs fine but all I did was pour some gas in the float bowl, start the engine, and run the carb dry.

Can I apply some gentle air pressure to the fuel tank vent, and thereby force gas through the line, through the pump, and all the way up until it fills the float bowl and raises the float?

I want to be as gentle as possible on the starter and battery when I crank this thing up the first time.
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RCP Phx
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PostPosted: Wed Dec 01, 2021 1:08 pm    Post subject: Re: Purge new fuel system? Reply with quote

Just pull the spark plugs, you "can" do damage the other way.
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PostPosted: Wed Dec 01, 2021 3:05 pm    Post subject: Re: Purge new fuel system? Reply with quote

You shouldn't need to apply pressure. On a stock car, the tank is above the fuel pump so it will gravity feed. If you've built your kit car correctly, the same should be true. Very Happy

If you only have a couple gallons in the tank, you may need to elevate the front of the vehicle a bit to get the fuel flowing back. Pull the inlet line off the fuel pump and verify you have fuel there, then you should be set.

If you want it to fire right away without waiting for the pump to pump fuel up to the carb, then pre-fill the float bowl.
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Ulu
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PostPosted: Wed Dec 01, 2021 7:03 pm    Post subject: Re: Purge new fuel system? Reply with quote

RCP Phx wrote:
Just pull the spark plugs, you "can" do damage the other way.


Thanks, but no way. Too much work. Too much chance of getting dirt in the engine.

What do you think I might damage?
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RCP Phx
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PostPosted: Wed Dec 01, 2021 7:32 pm    Post subject: Re: Purge new fuel system? Reply with quote

Ulu wrote:
RCP Phx wrote:
Just pull the spark plugs, you "can" do damage the other way.


Thanks, but no way. Too much work. Too much chance of getting dirt in the engine.

What do you think I might damage?


The diaphragm in the pump.
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PostPosted: Wed Dec 01, 2021 7:47 pm    Post subject: Re: Purge new fuel system? Reply with quote

Just hook up the lines, splash some gas down the carb and fire it up. Why make it complicated? The gas should run to the pump by gravity, then the pump will pick it up from there when you start the engine.
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Ulu
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PostPosted: Wed Dec 01, 2021 11:51 pm    Post subject: Re: Purge new fuel system? Reply with quote

Pruneman99 wrote:
Just hook up the lines, splash some gas down the carb and fire it up. Why make it complicated? The gas should run to the pump by gravity, then the pump will pick it up from there when you start the engine.


I was trying to make it simple, and you guys have got me taking out spark plugs and removing the air cleaner. Previously I just popped off one fuel line and filled the float bowl with a funnel. I didn’t try to run the car off the fuel pump though.

I was just gonna stick a rubber hose over the fuel tank vent and blow some air into it gently until it forced fuel past the fuel pump to the float bowl. I decided not to do this yet, because if the diaphragm is ruptured already I will simply pour gas into the crankcase.

BTW This is a custom bodied ‘73 Volkswagen standard beetle and the fuel tank is a little bit lower than the stock position. The bottom of the tank sits almost on Napoleon’s hat, and it’s a bottom feed.
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PostPosted: Thu Dec 02, 2021 7:40 am    Post subject: Re: Purge new fuel system? Reply with quote

Ulu wrote:

BTW This is a custom bodied ‘73 Volkswagen standard beetle and the fuel tank is a little bit lower than the stock position. The bottom of the tank sits almost on Napoleon’s hat, and it’s a bottom feed.


As long as the level of the fuel in the tank is above the fuel pump it will gravity feed. It doesn't matter where the bottom of the tank is. Just fill your tank to the top and let gravity do the rest.
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Ulu
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PostPosted: Thu Dec 02, 2021 8:30 am    Post subject: Re: Purge new fuel system? Reply with quote

The fuel level does feed the pump. Barely. I lifted the nose for more, and I still get no output.

I gotta take it off. It doesn’t pump and I hope it’s stuck valves, and not a ripped diaphragm. I just changed the oil.

Don’t take this the wrong way, but I’m gonna go smell my dipstick and remove the pump.

I have an electric pump I will use temporarily. I was prepared for this.
Just not prepared enough to have a new pump in hand.
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Ulu
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PostPosted: Thu Dec 02, 2021 8:39 am    Post subject: Re: Purge new fuel system? Reply with quote

Guys, I don’t have, and never have had, a standard beetle from which to take measurements.

Now looking at an old Volkswagen engineering drawing, with just basic dimensions and outlines, it appears that the bottom of the fuel tank is approximately the same level as the fuel pump.

I smelled my dipstick and of course it did smell like gas, because the reason I changed the oil is it had gasoline in it.

I was blaming the carburetor, but this car ran good on the carburetor.
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PostPosted: Thu Dec 02, 2021 1:19 pm    Post subject: Re: Purge new fuel system? Reply with quote

A good working stock mechanical fuel pump can pull vacuum with air in the fuel line, and so, it can prime itself and even lift fuel up from below the pump.

If it is not priming with the tank base near the level of the pump, then you have an issue with air leaking in probably that split diaphragm that filled the engine with fuel. If you pressurise the tank, all you would do is push more fuel into the engine as well as the carburettor.

Unbolt the pump and hold it level with the top of the engine, operate the lever with your finger and see what happens..

My old pump used to suck so hard it would hold a solenoid shutoff valve down, so the next time I turned on the ignition and powered the solenoid valve, I would not get any fuel, and I would drive forward about 20 feet and run out of fuel as the float chamber emptied..

If the pump has a fractured diaphragm then it will just pour fuel straight back into the engine. You will likely also see fuel wetting the pivot pin.



The reason for removing the plugs is to lighten the load on the bearings which will not be fully lubricated if an engine has been left "dry" for a while.

It also means even if there is oil pressure built up, you can crank for longer without damaging the starter motor or the battery.
Compared with maybe getting dust into the spark plug holes, the cost of bearings, starter motor etc. is considerable.
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Ulu
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PostPosted: Thu Dec 02, 2021 5:38 pm    Post subject: Re: Purge new fuel system? Reply with quote

My plan was to pick up a new fuel pump, but too many other chores came due today: thus no progress.

I blamed a stuck carb float rather than a ruptured diaphragm for this gas leak, because when I test-drove the car it ran great cold.

BUT it was running on an electric fuel pump. SO, Both things could be true at the same time: bad mech pump and stuck float.

This car was delivered to my house and I only test drove it then before taking delivery and putting it away. Gas had leaked into the car, and the whole car smelled like gasoline when it was delivered. It also had a minor seepage in the main fuel line connection at the tank, and I did not trust the stock fuel line at this point. I repaired all the air leaks at the tank, and ran a 8’ rubber VW fuel line from the tank to the pump. So there’s a clamp on each end and that’s it.

Image may have been reduced in size. Click image to view fullscreen.


I changed the oil before starting the car this week, and it had sat cold for 18 months. All the time there was about a pint of gasoline in the oil and I never realized this until I went to change it. The oil was extremely clean for a Volkswagen, and it was a pint overfull and smelled like gas. It was a little thin, but who knows what weight oil was put in it. The lifters sure didn’t seem stuck.

I used warm oil and I changed it in a warm garage, and my oil pressure came up right away. This engine seemed to have lots of torque but did not seem very tight overall. Then again I never got it warm. On the test drive,I drove it around the block and into my garage and shut it off, and that’s all I’ve ever seen it run except in a video.

Anyhow, I don’t think this fuel pump works because it was not able to suck a vacuum and I didn’t try to prime it. Tomorrow I will go and buy a new fuel pump for it. We have six Napa stores in the local area so one of the will have it.
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Ulu
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PostPosted: Sat Dec 04, 2021 8:02 pm    Post subject: Re: Purge new fuel system? Reply with quote

Woohoo! Success!

The pump pumps ok, and my suspicions were correct. The previous owner installed an electric pump because he had seepage=air leaks in the fuel line(s).

My issue was that I had the feed and return lines exchanged on the pump. I bled the fuel line and corrected the routing and she fired and ran.

Having bypassed all the original BS with new fuel hose eliminated the leaks and the engine runs fine with the mechanical pump that was on it (which appears to be a relatively new manufacture: it’s crimped, not screwed.)

Thank you to all the folks who took the time to respond here and try to help. Everything seems to be working great on the car except that I forgot to polarize the generator, and it has been still for 18 mos.

It has been over 30 years since I had to polarize a generator. I haven’t changed anything except the wiring so it just didn’t dawn on me immediately that having sat for a year and a half the magnets just went dead.
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