testing a manual fuel pump

[J-Gaz.]

Hello all-

I have ran some searches looking to find info on how to test my fuel pump. didn't find what I was looking for so... here is my question:

First, some back story: rebuilt the engine last summer, parked the car late september. everything was fine then. now it doesn't look like the fuel pump is pumping any fuel.

Q: I would like to do a test of some kind before I buy a new fuel pump and then find out that my fuel line was clogged. so, does anyone know of a test I can run?
Thanks for your help.

Its a single port 1600 in a 70 beetle.
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1970 Beetle | Basically Stock 1600 SP

[jamesdagg]

You can remove the hose coming from the tank and blow in it and listen for bubbles in the tank.

Then you need a cheap pressure gauge and a T to fit it in. Squirting into a jar is not good enough you need to know the pressure.

Did you put a new pump in? Push rods come in 2 lengths depending on the type of pump.

jim
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[Eric&Barb]

Sittting long enough the carb and fuel pump can dry out of any fuel.

You can take a plastic fuel filter and cut it down into a fuel proof funnel.

Then pour a little gas through the funnel with it attached to the fuel line into the carb. Also good to drip a little gas into the fuel pump to prime it.
The gas in the carb will allow the engine to start right off and with the extra engine RPMs the pump most always starts to pump fuel.
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[J-Gaz.]

[Bruce]

Here's an easy way to test it. First do the test Jim stated above, blow through the hose back to the tank.
Then remove the 2 nuts holding the pump to the engine and hook up the fuel lines to the pump. Using your thumb, push on the lever where the stock pushrod does. Keep pushing it while listening to the wheezing. Eventually you should hear fuel being pumped. Bolt it back on, drive away.
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[Russ Wolfe]

Is the rear of the car higher than the tank?? The pump could have problems sucking fuel that far uphill.
If the pump dried out while sitting, the valves in it could be not sealing well. Once they get wet with gas, they will probably be OK.
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[J-Gaz.]

[J-Gaz.]

Hey just wanted to let you know that I got it figured out.

looks like she needed the carb bowl and the fuel pump primed.

did all that, primed the fuel pump by hand and put in a new fuel filter, and she was good to go! Guess she just needed a little love!

Thanks again.

Justin.
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1970 Beetle | Basically Stock 1600 SP

[J-Gaz.]

And... It's doing it again... HA! Man, how wild.
This engine has been through it - I got a few good miles on it, but it's back to the hiccup and feeling like it's starved for fuel while driving.

It feels like someone pinches the fuel line for a quick sec and the engine just gets no fuel.

I had taken it out to my mom's for the 4th - about a 60-mile drive - after doing Car's and Coffee at the lake yesterday morning, where it performed great - but the drive out to my mom's it hiccuped a couple of times.

Then on the way back a few more.

It feels like it's running out of gas for a quick second.

So, I stopped for gas, and disconnected the condenser, and cranked the engine a few times to push more gas into the fuel filter.

Crank using the key, count to 10. Rest.

Did that 4 times.

Hooked up the condenser and drove off. Seemed fine for about 30 miles, then the hiccups again.

Also suffered power loss driving up Grade. I'd lose about 10MPH trying to go uphill, from 75 down to 65... So frustrating. Probably due time for a valve adjustment and oil change - In the past when I suffered some power loss like this it was due to the heads getting a little loose.

Anyway - Seems too intermittent to be a bad fuel pump, plus I'm driving it about every 2-3 weekends now, vs before when it sat for a year or more between drives.

Long story tolerable.
I'm going to do the Tests that Jim outlined (@jamesdagg). and @Eric&Barb 's priming technique.

QQ: where can I get an inexpexive fule pressure Tester as Jim mentions on a "T"? Is this something I can get via amazon or harbor freight?

I still don't understand why Blowing into the Tank and listening for bubbles will be helpful?

Thanks all-
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1970 Beetle | Basically Stock 1600 SP

[mukluk]

@J-Gaz.
Both Amazon and Harbor Freight will have a cheap pressure tester that comes with a T fitting, you can also often find them at your FLAPS. Be sure to get one for carbureted engines and not fuel injected -- the latter use much higher pressure and typically won't read the low pressure carbs use accurately. An example of one you're looking for is linked below, this type also having the useful advantage of being able to read vacuum as well as pressure.
https://www.summitracing.com/parts/ino-3620
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1960 Ragtop w/Semaphores "Inga"

[vamram]

Are you sure it's a fuel issue and not an electrical one? A coil going bad will cut out. My experience has been that a bad coil stops firing when it gets hot so whT you're describing is not that exactly bur I'd check oil and condensor. Ashman40 and others have provided some great detail on testing both, I'm not very proficient with those tests so will leave it to samba search or for them to pipe in.
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[J-Gaz.]

Thank you for this.
@mukluk - I'll give that a shot and see what I get.

@vamram, Yes fairly certain it's not the coil, I can run a test on it with my ohmmeter, But There is some noticeable improvement to the performance of the car when the tank is full vs when it's getting low.
My assumption is it has a bit to do with the fuel pressure generated by the volume of fuel in the tank...? If that makes sense - just sheer gravity pushing fuel in vs the pump pulling and pumping from the tank.

Also, I've run out of gas a few times in my life, and it has the same sensation for a second or two before it catches back up.

[J-Gaz.]

@mukluk - I just went out to the garage and as suspected, I have that vacuum/ Pressure tester.

So I'll give the pressure test a go once I can find a popper-sized T fitting for the fuel line.

Also, I noticed that the Fuel Filter is Way more full than it was yesterday after driving the car for a while.

one of the reasons I tried priming the car last night by removing the condenser lead and just cranking the engine is because I noticed when I popped the decklid after filling up that the fuel filter barely had any fuel in it.

So, I just tried to prime it to get more fuel in the filter.

Does anyone have any suspicions why the fuel filter may show less fuel at higher speeds than when driving in town?

It's almost as if my fuel pump doesn't pump enough fuel at high speed to keep up with the demand?

Strange to think about because it smells like it is running so Rich too.

More questions than answers at this point... that's for sure.
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1970 Beetle | Basically Stock 1600 SP

[Dougy Dee]

When you rebuilt the engine did you install a new fuel pump isolator? (The black Tee thing that fits under the fuel pump. )
A few incidences lately of them binding or grabbing the pump pushrod.

[J-Gaz.]

[Starbucket]

Did your old fuel filter have a lot of rust in it? The tank might be full of rust and its intermittently plugging the fuel outlet causing gas starvation. You can remove the tank gage and look inside with a flashlight.

[J-Gaz.]

[ashman40]

From your description the issue only shows up while you are on a long distance drive or while driving up hill. This to me sounds like a fuel delivery issue from the tank to the carb. Your 40yr old car may have sediment build up in the tank and/or in the lines. This will restrict the flow at higher rpms... on long drives.

My first question is when was the last time you replaced the fuel filter? Fuel filters should be replaced periodically (every 1-2 year). One problem I see is people look at their "see through" fuel filters and judge when to replace the filter rather than just replace it every/every other year. They let them go too long because "they look good". This is why solid metal canister filters are good. You can't see into them so you have no choice but to replace them on a schedule, or that is the idea.
Depending on the model of your car you may have have multiple "filters". Some Beetles had a screen at the bottom of the fuel tank. You remove the fuel outlet or a screw at the bottom of the tank to replace the screen. Most people have an inline fuel filter in the segments of hose below the tank; along side the left side of the transmission; or in the engine compartment before/after the fuel pump.

Fuel hoses also need to be replaced every couple years. They deteriorate with exposure and in some cases ethanol. If you cannot recall when the hoses were last replaced, replace them along with any fuel filters.
If you have never blown the center tunnel steel fuel line clean, do this with compressed air. Catch the gunk in a rag.
Remove the fuel tank outlet (if possible) and flush out any junk from the bottom of the tank.
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AshMan40
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'67 Beetle #1 {project car that never made it to the road }
'75 Beetle 1200LS (RHD Japan model) {junked due to frame rot}
'67 Beetle #2 {2019 project car - Wish me luck!}

[Cusser]

[J-Gaz.]

Funny you should mention this. I've been searching to form now for tips on how to clean the fuel system.
After looking at that fuel filter, it got me thinking...

My car is a 70, and I've not yet verified via internet searching if it had an in-tank filter - But I've seen a few parts for sale.

Seems like there could be a lot of rust/ gunk in the tank.
I've had the car since 2004 I think, and I've not done anything with the fuel tank, sending unit, filter, or any of that up there - So I've got to imagine after all this time, it may be suffering from a fair bit of gunk clogging it up - whether cleaning that up would fix my "issue" or not is the rabbit hole of ACVW's

The fuel filter and lines are new. I rarely drive the car. I'd have to look at my receipts (or could look at some old posts) but It got new lines and filter in January 2020 when I had to have the crank drilled to an 8 dowel.

I think the filter is newer because I had some work done on it a few months ago, Maybe February, when I got new shocks, headlights adjusted, Idle adjusted - and the re-jetted my carb (not sure why the shop decided they needed to do that).

Regardless, I'll probably have to have a shop do any of the real work - I don't have much in the way of tools or space to work on it on my own aside from a few maintenance things here and there.

But, I can replace the filter between the fuel pump and the carb, that's easy enough! ha!