CIS to Carbs '74 - installation best practices

[Porsche_911s]

Zenith 40's '74 2.7

EDIT => Updated thread with parts used

Zenith Jetting: Venturies 34, Main 145, Idle 55 ~ 60, AC 185, Anidles 130

Fuel lines: CIS fuel lines are fine if lines are in good condition. Older lines will have to have a line pushed over them and clamped with EFI clamps. '78 lines and newer have metric ends and either lines will have to be made or fittings converting to barb can be used. I went with Marine grade fuel line rated to 100 PSI. 5/16 line

Fuel regulator: Started with a Holley that had no return. I was unsure of the pressure with an inline gauge, switched to the PMO regulator with a return line that had a built in gauge. Felt more comfortable with this setup.

Fuel pump: Went with an Airtex fuel pump that puts out 5 to 9 lbs with a 30 GPM output. Easy to install and small enough to install in the front if the original fuel pump was located next to the fuel tank.

Fuel filter: Either use an inline filter before the regulator & one to each carb or something like a water/fuel separator. I live in Houston so I went with a "Cool Zone" water/fuel separator that filters down to 2 micron.

Ignition: I had problems getting the carbs tuned, went with a MSD 6AL and MSD high vibration coil. This solved fouling plugs while trying to get the carbs tuned. A properly tuned carb and CDI box will work fine.

Wires: Went with Nology wires because I got a good price on a used set. If I had to buy new I would have went with the Magnacore.

Plugs: NGK5ES, 6ES, 7ES gapped at .40 with MSD or .35 with CDI depending on engine setup

Distributor: Had mine re-curved by Barry in Detroit. Or a new RS distributor will do the trick. There is a MUCH better power band with the re-curved distributor. The vacuum retard can be unhooked or removed at the time of the recurve.

Exhaust: '74 exhaust and the muffler of your choice. I went with a Magnaflow dual in/dual out. Was a tad loud and ended up putting Pacesetter tips to tame it down a bit. I recommend putting bungs in both sides of your '74 exhaust if you take it to a muffler shop for the exhaust work. For "future" upgrades. I also went with 2 1/2" pipe and would go smaller if I had to do it over again.

Air intake: K&N filters with rainshields or original air box for carbs.

Breather (engine vent): Breather tank or original air box for carbs with breather port. I went with an Ovalcraft breather tank.

Power brakes: 3 to 4 manifold ports will have to be tapped to supply enough vacuum to power the brake booster. I have 3 and it seems to be enough and the engine does not suffer. Remember to install a check valve.

CAM: If you have carb P&Cs the sky is the limit for CAMs. If you have the CIS setup, you can upgrade to the SC CAMs (which will require SC CAM towers) or go with a regrind like the DC 10 grind (drcamshafts.com).

Tuning: Unless you are a pro, I'd recommend getting a Gunson gastester, LM-1, or LC-1. The gastester will help set the mixture at idle the LM-1 or LC-1 will take advantage of the bungs you had installed in your exhaust. They use a wideband O2 sensor to feed a laptop data. Other tools that are a MUST are Float Gauge by PMO, Synchrometer, timing light, and something for reading the idle at the back of the car.

Other items would be printer to print off all the suggestions you'll find on this board. Read and then re-read!!

I hope this helps someone!!

[moneymanager]

I replaced my CIS system with PMO's a year or so back. The CIS lines from the tank are just fine. PMO says set the fuel pressure should be around 3-4 lbs (they include a gauge which it sounds like you have as well). I ran mine at 5 lbs for a few days before finding it was too high so I doubt 4 lbs is too high.

[ianc]

[smartass]Best practice is to leave the excellent CIS alone and not install primitive carbs[/smartass]

Sounds like you're a little far along for that advice however.

ianc

[Porsche_911s]

Yes, a little far along for that advice. However, I am not selling or parting the CIS and will keep it nice and stored.

Moneymanager well come to the board!

Thanks for the reply

[RoninLB]

It's a Carb eat MFI world imo.

[jwetering]

Originally posted by moneymanager
I replaced my CIS system with PMO's a year or so back. The CIS lines from the tank are just fine. PMO says set the fuel pressure should be around 3-4 lbs (they include a gauge which it sounds like you have as well). I ran mine at 5 lbs for a few days before finding it was too high so I doubt 4 lbs is too high.

Double that - CIS lines are fine. I too ran an unregulated fuel pump putting out about 5 psi for a while, but you know you'll always be wondering about those needle valves, and even the slightec=st hiccup will have you suspecting fuel pressure.

A really nice (and not at all expensive) setup is the PMO fuel bars and pressure control unit. It will cost you less than $200, but will give great fuel delivery. The PMO system has a gauge and uses the CIS return lines so your fuel keeps circulating. You can use the Holley pump and step the pressure down to whatever you want.

I have a couple of pictures here somewhere...although they're not great. Note that in these pictures the return line is connected to the input on the pressure control unit and the input line hadn't been connected yet. I was in the process of sorting it all out when I took the picture.

In case you were wondering....the red lines in the back are my power brake vacuum lines...tapped into my intake manifolds.

[Vipergrün]

I was gonna recommend contacting PMO, but since Jasper already did....



Moneymanager, welcome to the boards, lots of fun around here. Please note that a formal introduction and pics of your car are required. I grew up in SB (well, Goleta), wonder if I know you?

Porsche_911S, good luck with your project, don't be discouraged. The carbs should wake your engine up. Has she been rebuilt?

[Porsche_911s]

Yeah, the engine was rebuilt. It was rebuilt for CIS and I will be changing the goodies a little later to take advantage of the carbs.

The setup looks great! I'll play around with it and see what happens.

[Mike Bonkalski]

You might want to take a look at your fuel supply setup. It looks like you have a loop setup, but no return. If your not running a return, shouldn't you just "dead-end" at the fuel rail ends??

[jwetering]

Originally posted by Mike Bonkalski
You might want to take a look at your fuel supply setup. It looks like you have a loop setup, but no return. If your not running a return, shouldn't you just "dead-end" at the fuel rail ends??

Yes - I know - look at my comments. The picture was taken before the installation was complete. There's a fuel filter on the input line now as well, makes three filters in total and one for each of the two carbs.

Hang on - just reread your post. It's not a true loop setup. Each carb is fed individually, but the two carbs are connected around the outside (if you know what I mean). Not really necessary, but it does gurantee fuel is available for all four floats in more or less equal measure. The PMO pressure control unit has two outputs. You can't really make a true loop using that product, and arguably you wouldn't want to anyway because the last float bowl in the chain could get starved.

[Porsche_911s]

Did your power brakes take two vacuum sources?

[jwetering]

Originally posted by Porsche_911s
Did your power brakes take two vacuum sources?

No - I drilled four of the 6 intake runners and tapped in
swagelock (compression) fittings. Then I used 1/4" brass tubing and more swagelock fittings to tie them all together into the existing power brake line to the booster. I can take closeups if'n you want. It actuallly looks and works really good (well).

[Porsche_911s]

Reason I asked is because I think only one of the runners I have were tapped for a vacuum source for power brakes (or other item needing vacuum).

[jwetering]

I spoke with Bruce Anderson at the time when I was doing it and he recomended four taps. He said 6 was too many and two were too few. Sure enough I can't tell the "new" power brake feel from the old.

[Porsche_911s]

Pics of the setup would be great.

Thanks,

[Porsche_911s]

What size fittings did you use? (for the regulator and fuel pump) Would you use 1/4 or 3/8?

[RoninLB]

big cams should need at least 2 lines for the booster. I'm doable with 1 line but 2 would be nice. 6 lines with 6 dash vac gauges would be too much. A digital bar graph with roating numetical in a

2.25" dash gauge would be trick.

[randywebb]

also check to make sure all the ports match

[jwetering]

I posted my power brake setup in a separate thread - so as not to hijack this carb thread. The link is here

link to power brake setup

I also snapped a couple more pictures of my PMO fuel regulator setup:

[RoninLB]

I see what's happening now. You used 1/4 tube. The stock single PMO is one large fitting. Is your cam more radical than the MFI S-cam?

btw.. nice clean job.