Fuel Pump options

J11 · 04-28-2008, 09:07 AM

I tested the output of my '67 912 fuel pump. Feels like carbs are starving past 1st gear--

4psi without fuel filter, and it drops to 3psi with.

Fuel filter looks empty until floats open up a little, then a squirt of gas shoots through, then it looks empty again. Can run through first gear fine, shift to 2nd, and it bogs and starves.

If I give it TINY throttle when I hit 2nd, it'll keep up. If I give it normal throttle, it starves. If I keep it floored through 4 seconds of starving, it'll come on normal...

Fuel pump?

Jaems · 04-28-2008, 09:54 AM

The fuel pressure is fine. You might need to rebuilt the carbs. Do you have fuel in the float bowls or is the fuel filter backwards? There is an arrow to point in the direction of the flow to the carbs.

J11 · 04-28-2008, 09:57 AM

I'm stumped.

Fresh Carbs. Fuel in bowls. New filter, installed correctly. Floats set correctly... stumped.

Jaems · 04-28-2008, 01:38 PM

Then it could be with the fuel pump try an electric fuel pump. If the problem goes away then you need to rebuild the fuel pump. There are several cheap electric types that you can use for a test.

An other thing if you have a 061 distributor the vacuum retard diaphragm could be shot. Otherwise the carbs need to be taken apart and cleaned. If it was an Becker re-manufactured Solexes. They need to be blowed out before you install them. Make sure that all the jets, airs and etc. are clean and clear. If you haven't already do it. Make sure that your valves are adjusted correctly.

J11 · 04-28-2008, 02:06 PM

I appreciate the reply...

050 Dist. w/ Petronix. Are those testable?
Recently rebuilt carbs with jet combo working great in the past (IDFs 32 vent / 135 main / 52 idle).
Put in a new coil.
Checked the valves too! I'm stumped!

I'll try an electric pump-- I have one somewhere. Do I just leave the hoses off the Mech pump, or do I need to remove the pump? Block off?

J11 · 04-28-2008, 02:21 PM

**edit - dupe**

cgarr · cgarr's Garage

How is the idle? can you change the idle with the adjustment screw? you may have a flake of dirt of one of the idle jets which will keep it from transitioning from the low to high speed jets. It does not take much to really feel it in these engines. If you pump the peddle which works the accelerator pump will it work thru the starving spot? And what E tubes are you running?

J11 · 04-28-2008, 09:11 PM

Accel. pumps squirt. I will go around the block tomorrow and try pumping-- I know what you mean... could indicate if the bowls are empty. I could also shift to second, give it a little gas, and as it starves shift to neutral & cut the key right away... remove the top of the carb & check the bowl... I guess... is that insane?

Should the fuel filter be totally empty all the time? Until the floats open up, and enough gas squirts by to fill them again, then stops & the filter is empty again. I guess I've never paid the closest attention, and I don't always have a filter in the engine bay anyway, but seems it shouldn't be empty?

I gave the idle jets a quick look since it seems to starve well past their cut out-- I'll check closely tomorrow though. Mains I checked, and all appear clear. F11 tubes. Have been running about 1 1/8 turns out at sea level...

maybe368 · maybe368's Garage

I run both an electric fuel pump as well as the stock one, which acts as a preassure regulator. I mounted the electric in the smugglers box an pull tied a dead man type push button switch to the front trunk lid cable. I use the electric to fill the bowls and the filter when it has sat for more than a day or 2. My friend runs an electric and stock all the time, but I am afraid of the electric running on in case of a leak. Good luck Mark

kdfresto · 04-29-2008, 10:23 AM

Are you sure that it's starving? The only way to tell is to check fuel pressure while driving. Buy a pressure/vac gauge, hook it up with long hoses, and tape it to the back window. Look at it thru the RV mirror and see what's happening.

Then check volume. How many GPM is the pump delivering ?

Might have to rebuild that pump. There is a correct procedure to rebuild the Porsche and early VW pumps. You must preload the diaphram before screwing the 2 half's together. The spec should be in the repair manual.

J11 · 04-29-2008, 10:38 AM

Quote:

Originally Posted by kdfresto

Are you sure that it's starving? The only way to tell is to check fuel pressure while driving. Buy a pressure/vac gauge, hook it up with long hoses, and tape it to the back window. Look at it thru the RV mirror and see what's happening.

Great idea! I replaced all the fuel hoses and then this started happening... is there some sort of pre-load/priming procedure I missed?

Thanks!

maybe368 · maybe368's Garage

Did you replace the short line from the tank to the hard line that goes through the tunnel? When I replaced mine the first time, I stuck it back together and when I installed the electric pump I found that I had kinked that line...possible since your problem started after you replaced the lines.

kdfresto · 04-29-2008, 01:48 PM

Like he said.....
Damm good idea.

J11 · 04-29-2008, 02:51 PM

that IS a good call-- but I haven't got to the front yet

I'll try some things suggested here when I get home and post back...

djdsc · 04-29-2008, 08:20 PM

Remember the old adage, “Most carburetion problems aren’t.”

Having said that, if you are running a clear plastic fuel filter ether before of after the mechanical fuel pump you will seldom ever see any fuel in it. At times like right after shut down it might appear to be full but running it will not.

Weber’s are sensitive to fuel pressure; if you are running greater than 3 psi then you run the potential of overpowering the needle valve. Unless your floats are set up terribly low and if you have fuel coming out the pump jets when pumped you most likely have enough fuel in the bowls for running. Did you simply remove the fuel line from the output side of the pump and see the discharge. There is no need to install an electric fuel pump on these cars; spend the same money on a rebuild kit for the mechanical if you need to. Running both is not a recommended procedure unless you are only using the electric for priming the lines and certainly not without an automatic shut off in the case of an accident.

It sounds like you are running Weber’s, a point not clearly mentioned. There are three, now four with the EMPI’s, versions of the Weber 40 IDF carbs. Each have their own characteristics, especially at transition which is where it sounds like you are having your problems. The early style 40IDF’s have the most problems very much like what you describe. You must have your accelerator pump set correctly both in volume and duration on any model Weber or any carb on these cars for that matter. What size air corrector, just curious?

J11 · 04-30-2008, 08:18 AM

200 airs... it all ran fine before it didn't

Fuel pressure is mentioned above @ 3-4 psi.

Went out to the car last night, but I had left the drivers door cracked for 2 days & the interior light drained the battery, lol. It's a small light weight batt. I plugged in the charger, shut the garage, and took the night off. I can't win!

I'll post a follow up tonight.