'74 CIS issues

[coolngroovy]

Hi guys, I have a little problem.
I just tried to start my 74. I have had issues with the fuel before, but i think i have almost got them sorted.
This one baffles me though!
I turn the fuel pump on, wait for the system to prime, hit the starter, then it runs. But not for long.
I can hear the fuel pump stammering, so it cant be pumping constant.
When i hold the prime plate up[bleeding the system], i can hear the injectors priming. Same deal, runs for a few seconds. Almost like it is running out of fuel.
After doing this a few times, holding up the primer does nothing!
The injectors are not singing. There is no resistance of the primer plate.
Am i simply out of fuel supply?

I have a new set of injectors on the way from our host.
I have been thinking i have a bleeding/leaking injector. That is why [i think] i have been having these problems. It has always been difficult to start, or re:start.

Any thoughts?
Cheers, Col.

[hifeverz]

I had a similar problem on my '74 911. I went through a couple of fuel pumps (defective rebuilt unit) before success. I also needed to change the filter, accumulator and had the tank cleaned out as it(tank) was full of flaked rust clogging the hoses. It is a 34 yr old car that needs attention to these items. I spent a ton of $$ on body work/engine (see pic . . . of my '74 911).

Good Luck
Hz

[Bobboloo]

Sounds like a fuel delivery problem.

Possible causes:
1. Out of gas (ignore what the gauge shows they are often misleading)
2. Pinched or clogged fuel line.
3. Clogged fuel filter
4. Bad fuel pump

[wowzer911]

+1, I'd also recommend checking all fuel lines for leaks, if fuel pump is good but audibly stammering, it should hum smoothly.

[Mukilteo911]

Sounds like the filter to me

[coolngroovy]

pump is new. As is the filter.

My train of thought is leaning toward an injector bleeding out. Thats why i have ordered new ones.
I dont understand why lifting the bleed plate wont bleed the injectors!

[wowzer911]

I think you're starting at the wrong end. You said your self that you think the pump is not pumping constant. It sounds like lack of fuel delivery, instead of correct fuel pressure but leaky injectors. Just my 2 cents. Good luck

[surfdwn]

I vote for the fuel gauge being wrong. I had an '80 SC that did the same thing. I found out that the fuel gauge was very inaccurate below 1/4 tank.

David Nolen
'70 911T

[ossiblue]

Originally Posted by wowzer911

I think you're starting at the wrong end. You said your self that you think the pump is not pumping constant. It sounds like lack of fuel delivery, instead of correct fuel pressure but leaky injectors. Just my 2 cents. Good luck

+1.

Your own experience shows that priming in ineffective after a few tries. Priming is to fill the lines from the tank to the injectors and once the lines are "filled" they should remain filled due to the check valve, fuel accumulator, fuel distributor set up--assuming all are in specs. You are losing fuel pressure in the lines while the system is under pressure, ie. delivery problem. It sounds like something is cutting off adequate fuel flow to the injectors. A leaky injector will not cause that problem.

Maybe start by running some pressure tests on your system, that will nail down immediately if you have a delivery problem. It's easy and cheap too.

[coolngroovy]

Thanks for the input guys.
It looks like i'me going to have to bite the bullet & buy a fuel pressure gauge.

Ironically, i was tring to start it so i could put it up on the ramps & pull the fuel tank for another clean!

Can anyone suggest a product for sealing the fueltank internally?

[Mukilteo911]

"Can anyone suggest a product for sealing the fueltank internally?"

I used POR's product for this, worked great. But I had the tank boiled out first. I think it owuld have been easyer to buy a good used one.

[coolngroovy]

Buying a used tank is not an option.

I remember reading through some threads on the subject.
For some reason, i remember POR not recommending their product for the 911 fuel tank.
Something to do with the plastic 'swirl', & possibly melting it. Though i'me not certain.

[azasadny]

Do you have an old burglar alarm in the system? I had an old Hofco that was cutting off ignition and fuel pump power intermittently and caused starting issues until it was completely removed.

[coolngroovy]

Thanks for the input Art.

I still think a bleeding injector is the culprit.
I will remove the tank, steam clean it again, air blow the lines again, replace the injectors, & put a pressure gauge on the system.
From previous q's i've asked, and the input i've recieved, i think it has to be done.
Otherwise i'me going to keep chasing my tail.

I think until i have the internals of the tank sealed, this is going to be a continuing problem for me.

One day soon, i'me going to be driving this thing in anger!

Cheers, Col.

[T77911S]

check fuse, relay, electrical connections.

[Grady Clay]

Col.,

Clean the tank and the screen filter in the bottom of the tank. Do not light into ‘sealing’ the tank internally. Most likely it will get ruined in the process.

There is a “Swirl Pot” in the bottom of all CIS tanks. This is an attempt to separate bubbles from returning (warm) fuel and prevent the pickup from getting any air when the fuel level is low.

Do some Pelican searching. There are several good threads with diagrams and images of cut-apart tanks. There is also one ruined tank full of POR.

The first order of business is to siphon all the fuel out through the gas gauge opening.

Next is to remove the screen filter from the bottom of the tank. You will want to have a new level sender gasket, a new screen filter O-ring and crush washer available.

With the two fuel hoses off the tank fittings, clean the pipes inside the tank. A high-pressure washer works well. Wash and rinse the inside of the tank. Let it air dry in the sun.

Reassemble with new gaskets and seals.

The “While you are there” project is to move the fuel pump to the front cross member (like Porsche did in ’76) and install new fuel lines and proper clamps and fittings. I like having the filter and accumulator under the front also. It is wise to insulate the fuel lines where they pass above the transmission and in the engine compartment.

This is good ‘vapour lock’ protection for hot Queensland summers.

Best,
Grady