CIS to Zeniths - Fuel Delivery?

[RedRacer]

Hi all, my first New Topic here!

I bought my first Porsche a couple of months back, a 1977S. The CIS was running ridiculously rich, so I bought a set of Zenith TIN40s. They bolted on fine, and I filled the bowls with fuel and ran them at idle for a minute and all is good.

But which fuel pressure regulator should I run? I am having a little trouble searching for parts on the Pelican website, but I think it might be this one:

PEL-PMO-PCU

Is this the one to get? There is no info on the product info page. And do I need anything else to plumb it in, and will the pump work without some kind of signal from the CIS?

Sorry if this is posted somewhere, but when I searched the forums I could not come up with the answer.

Great site by the way, makes Porsche ownership a little less daunting!

[sc_rufctr]

Try this link...

Porsche 911 Carburetion - Page 2

I'm sure the PMO one would work fine but you have a other options.

Good luck with the project.

[T77911S]

i have heard of people trying to regulate fuel injection FP down for carbs and it did not work. when i had my 914 and converted to a 6 with webers, i pulled out the FI pump and put in 2 lower pressure pumps, one as a backup. maybe now there are some reg's that may work. just something to think about.

a cis pump can put out close to 80-100psi.

[James Brown]

You need a fuel pressure regulator that has a bypass in it that regulates down to 3-3.5 PSI. Any make will work fine but the PMO unit is the easest "plug and go" way to go.

[RoninLB]

Bosch FI FP needs the by-pass reg w/return line

[VFR750]

PMO Fuel Pressure Regulator works great.

* Keep the high-pressure pump,
* Keep or substitute another high-pressure fuel filter.
* Remove the fuel accumulator.
* Add low pressure filters between PMO Regulator and Carbs

[RedRacer]

Awesome, thanks for the replies guys.

So I take it I have the right part then? Anything else I should order with it to make it all happen nice and easy?

And will my fuel pump work without the need for any creative wiring etc.?

Thanks again, this is all starting to look up!

[Porsche-O-Phile]

Yours is a 2.7L also? I'd be curious to know more about your setup. I (like you) am frustrated with the limitations of the CIS system and the fact that one cannot run hotter cams with it. While I can get (and have gotten) the CIS system pretty well sorted out, it was a monumental PITA and sourcing parts for them is getting more and more difficult - lots of exotic and impossible-to-find metric barbs, nylon hoses, banjo bolts, etc. I finally picked up a set of Zeniths and are rebuilding them - I have some info on jet sizes and venturi sizes appropriate to the 2.7 but would like to know what you're running to either validate or refute this information.

IMHO the Zeniths are awesome carbs - they're very well built and solid. I have no idea why they're frowned upon as they are so often around here. Webers are nice but I fail to see why they're better (in fact, the Zeniths are more advanced) and the PMOs (while nice) are absurd in terms of price.

Best of luck going forward - post up some info about your setup when you get a minute!

[RedRacer]

Mr O-Phile,

Yes the Zeniths sure seem a lot easier to work with than CIS.

Unfortunately I have no setup info, I bought mine on ebay and simply bolted them on. They apparently came off a 2.7. But all I have done is run them at idle after filling the fuel bowls to verify they would run. This is why I am chasing info on what pressure regulator to run, and how to plumb it in etc.

If there is any way I can give you any more info please let me know - measurements, serial numbers or the like, just tell me where they are and I will see what I can come up with.

[cjmurph]

Haven't had the long run (tranny problems) to completely verify but my zeniths ended up with .55 idle and 1.35 mains with stock venturis on stock manifolds. Really seemed to work well in my 2.7.
I understand that we can play with the accelerator and squirters to really help in transition and mine seem to be "backed off" compared to the previous setting on the 2.2 motor.

In regards to setup. My previous stock bosche fuel pump had failed and I bought the pelican replacement 901-608-106-00-M244 pierburg pump. Basically capped my return to the tank and went with the assumption that the low pressure pump would suffice. So far that seems to be working extremely well. I haven't measured/verified the exact pressure but I probably should.
Use to be a very helpful zenith guide or link on this site. Luckily I printed it out for reference because the last time I tried using it, it was defunct. Fellow pelican in Colo Bill Vassuer(?) had done a really good job of assembling some of the info that had bailed me out early on with zeniths.

Curt

[VFR750]

Originally Posted by RedRacer

And will my fuel pump work without the need for any creative wiring etc.?

I doubt my pump knows or cares there are Zeniths on the engine now. No changes at all.

The CIS fuel pump is a recirculating type. It uses the continuous flow of fuel to cool the motor. BTW< that is why running the tank dry is very bad, as the pump will overheat very quickly.

It needs the PMO style regulator with the return line hooked up to the tank, otherwise you'll burn out the motor. Other than that, it doesn't know where the fuel is going.