1975 911 running rough

[Jeffcalgary]

I have a 75 911 with dual weber carbs. i was out for a drive and twice the car started to bog down and it wanted to stall out. But quickly recovered and got me home. I figured i would change the two inline fuel filters before each carb. I did and when it started up it ran really rough and i can smell alot of gas in the air. I cleaned out the existing filters and put them back on same result. So i changed the fuel pump and the filter before the pump. Still same result. Running rough smell of gas in the air. Any ideas??

[zedsn]

Clogged jets?

[Jeffcalgary]

Can the jets clog after a fuel filter swap? Should also mention that the fuel pressure guage is reading 0 psi when idleing....

[zedsn]

I just went through this. I too replaced the fuel pump because my pressure was 0 at the gauge with same result. You have a screen in the tank and I would see if there is debris on it. It is like a filter. You can see it by removing the sending unit. I would not run the filter before the carb. My problem like I said still persisted after the pump change and I had a blocked fuel filter but my filter is before the regulator not on the lines to the carbs. Your regulator may be clogged now because of crud. I believe the ethenal is slowly eating away at my hoses and I ran a large fuel injection filter instead of those smaller glass see though ones. I would start and see why your pressure is now low.

[Jeffcalgary]

Ok. The fuel pump was a mr gasket 42s and had a filter at the intake. I removed the sending unit and looked at the fuel tank screen. Didnt look like there was any debris but super difficult to see it clearly. The fuel pump regulator is a non adjustable type. Can they fail?

[Uncle Enzo]

Clean our your idle jets. They will cause the car to stumble at low speeds. They are very prone to getting clogged with carbon bits. Takes all of 2 min to pull and clean them. There is one on each barrel.

[zedsn]

I would pull the fuel hose before the regulator and put the hose end in a glass jar or something and carefully hold it and have some one else turn the motor over to see if you are getting good fuel flow out of the line. Might want to pull your coil wire while doing this just in case if you go this route.

[Lapkritis]

I don't see a fuel pressure regulator in there. I have the same vintage weber/pmo setup. You raise fuel pressure by clamping the return line after the fuel gauge/ distribution block. I don't see a clamp either... that may be the problem?

Keep a fire extinguisher handy when you smell raw fuel.

Check for fuel leaks in the tunnel.

Idle jet cleaning:

Brief Pictorial - Idle Jet Cleaning on Weber 40 IDA ...

Brief Pictorial - Idle Jet Cleaning on Weber 40 IDA 3C

[Jeffcalgary]

Ok so idle jets are all cleaned out. Clamped the return line and showing 3psi. Still no change.

[Jeffcalgary]

**** i just notice two blown fuses in the engine bay...will have to change them tomorrow....anyone know which circuits they protect?

[zedsn]

What type of ignition are you running if running carbs? The very bottom one is a 12 volt switch source that runs my MSD box. As far as your fuel pressure you are going to have to remove your hose before the regulator and see the volume that you are putting out. Your filter before the pump could be the culprit and restricting flow.

[Jeffcalgary]

So super simple fix....the clamps at the fuel filters were too weak and it was sucking air lol