CIS to Webber's swap

[scrimpsher]

Getting close to finishing my project and need some advise on some items I am alittle stumped on and looking to see if anybody has been through it or has any good resources.

1.CIS to carbs I am undecited on a few things: I'm considering using the stock fuel pump and have new fuel filter as well as the pmo fuel regulator and would like to replace the fuel lines from the tank to the motor while I have the motor out. I'd like to do this just one time and would like to get the best lines possible. Pre-made is fine with me I would probably prefer it since I haven't really done any fuel line cramping I just want to get it done.

2. Is it a good idea to relocate the fuel pump since I have the car lowered 19 millimeters. Had elephant racing do my struts. And where would be a good spot for it if that was a good idea. I'm using the stock fuel tank for now eventually I may get a fuel safe.

3. Since I have the carbs and doing an MSD ignition and have a vacuumless distributor rebuilt and curved. I plan on just really minimal wiring and want to know what the absolute minimum is to start the car and shut it off. Since I no longer have she is I would think this would eliminate a lot and I'm getting ready to paint the engine well and I'm going to pull out the harness anyway.

So I would think I can get rid of 90% of the wiring that goes to the motor area except for sensors for the gauges, lights, starter, rev light and the ignition. Up the wire Gage to a zero voltage drop and add additional ground to avoid electrical traffic jams. Any advice or diagrams would be much appreciated.

Please keep in mind everything I'm doing to my a 1983 will eventually end up on a 1970 roller that I have waiting for my attention. This will solve some of the smog issues I have.

Thank you very much look forward to hearing responses.

[Ayles]

On your wiring harness you can reach out to timmy2 and get a plug and play harness for carbs. I used an old factory rs harness in mine and it had only the bare minimum.

[scrimpsher]

I will thanks for the referral on that one. Is that how you got the RS harness from?

[Ayles]

No, my father in law had a real one that I used. I did get all the connectors from timmy2 to plug the 6 pin connector directly into the msd box. Makes for very clean wiring.

[Gordo2]

I converted to carbs and simplified my wiring - by replacing all engine bay wiring with my own harness.

I went with the XDi ignition, so my setup is a little more complex. Meanwhile this thread may provide a little more insight to what you will be keeping - which for the most part, really doesn't eliminate much of anything, but if you do it right, significantly tidy's things up.
Engine Harness / Multi-pin Connector for Carb Conversion '83 SC

Good luck,

Gordo

[rattlsnak]

Stock CIS fuel pump is way to much.. It puts out upwards of @70psi whereas carbs only need @3-5psi. Even with a regulator, its way too much.

[Gordo2]

Originally Posted by rattlsnak

Stock CIS fuel pump is way to much.. It puts out upwards of @70psi whereas carbs only need @3-5psi. Even with a regulator, its way too much.

I initially used the stock CIS pump and PMO reg and I was able to get it dialed in to provide 3.5 PSI. Meanwhile the PMO pressure gauge needle / pointer would quickly fluctuate /bounce +/- 0.5 PSI. I'm not sure, but I think my return line may have had a restriction that contributed to the variation. I also heard that replacing the PMO gauge with a fluid filled gauge would nullify the gauge needle / pointer bounce issue.

I used the CIS pump for ~ 6 months after initial install. During this time I was troubleshooting an engine hesitation issue in the idle to main transition region (~ 3.5k RPM). I decided to swap the CIS pump for a low pressure electric pump in order to take the questionable fuel pressure fluctuation out of the troubleshooting equation.

Bottom line - opinions vary on using the CIS pump and reg with carbs, but all concur on the need to have a working return line if you do opt to stick with the CIS pump (otherwise the reg doesn't work). Of note, Mr. Richard Parr (PMO carb designer) - actually recommends sticking with the CIS pump (with a reg) when converting to carbs.

Good luck,
Gordo

[scrimpsher]

So what's the very best setup for fuel line/reg/pump to be able to just do it right not have any issues with the carb conversion? Going crazy with all these options.

[Ayles]

I use a mallory fuel pump. On the tank/pump side I use low pressure fabric covered fuel lines feeding into tunnel line built by boxstergt (Len) with m14 fittings at each end. At the rear I use braided stainless lines/an fittings from the tunnel to a racor fuel filter (110a) to the pmo pressure gauge, then into the carbs with PMO fuel rails. The mallory outputs around 7psi so it needs the regulator to get it down to the recommended pressure.

[Ayles]

Might be some helpful info here as well.

Show me your carburated SC

[zedsn]

You might want to keep your current setup if you don't have performance cams. Weber carbs get worse fuel mileage and with a stock engine I don't think that you will get any extra hp out of your motor running them. If you do run weber carbs I have had good success with a cheapo $26 3 to 5 psi electric fuel pump on fleabay. My 2 cents.

[78-911SC]

I believe BoxsterGT here on the forum is a good resource for your fuel lines. Can custom make to your needs.

[scrimpsher]

What cams are optimum? How do your job is it to drop them in? My motor is out right now.

[Pazuzu]

Originally Posted by scrimpsher

What cams are optimum? How do your job is it to drop them in? My motor is out right now.

Unfortunately, since you don't just "drop them in", it's a heck of a lot of work. Not like a V8 where you do drop them in.

take off all of the trim work, many accessories
remove valve covers, chain covers, chain tensioners
Remove rockers
Special tools to remove cams
Special tools to time cams, special gaskets and maybe some special sealant to put it all together

A few days of work if you know what you're doing and have all of the tools ready.

[Trackrash]

Originally Posted by scrimpsher

What cams are optimum? How do your job is it to drop them in? My motor is out right now.

Your conversion will require a bit of planning and conversions, so you are asking the right questions.

I have a 3,0 w/ Webers in my '71. I'm using the 6 pin CDI and all original '71 gauges.

I'm using a Facet solid state fuel pump mounted in my engine compartment. FWIW, my car had the fuel pump in the rear, so I am not advocating my setup, just saying it works. Your best option will be using a fuel pump in the stock location. You don't say what model of 911 you have. The E and S will have the return line to the tank, which is the configuration you should use. I am not using a return line, but if you have one, it is probably worth saving.

I replaced my fuel line with 3/8 copper tubing. It has functioned w/ no problems for the past 35 years. Others will say don't use copper. IMO copper is OK.

I am using stainless braided AN 6 fuel hose with hose clamps. As long as you are not using a high pressure fuel pump hose clamps will work fine.

As far as wiring goes, it will require a custom harness. This will also incorporate the engine's panel with the regulator and ignition.

You will have to wire up the gauge sensors, the alternator, starter, and the ignition. I disassembled the harnesses from the '71 and the '78 from my motor. I used these to create a hybrid harness to work in my car.

[Trackrash]

Originally Posted by scrimpsher

What cams are optimum? How do your job is it to drop them in? My motor is out right now.

Do you have Wayne's How to Rebuild 911 Motors?

Lots of discussion on cams for these motors. To have worthwhile cams you will need to also change out the pistons.

Do a search in the engine rebuild forum.

[Jack Stands]

I used a Pierburg low pressure fuel pump mounted up front by the steering rack with dedicated switched power. Allows me to turn off the fuel pump a bit before parking the car to lower the fuel level in the float bowls to help with percolation in the carbs. But, if the CIS system is working, you won’t get any benefit from swapping to the Weber’s other than a great sound.

[Ayles]

Id also think about adding an inertia switch that will kill the pump in an accident as you will no longer have the cis parts that will do that.

[unclebilly]

I've done this twice now.

Get a VW fuel pump, there is a Bosch Motorsports variant that puts out 3-4 lbs which is what you need for your Webers. It is a direct replacement for the factory pump and looks identical. We took this approach on the chump car.

On my other race car, I have the Carter pump which is a POS. It puts out 5 psi so I have to regulate it down to 3.5-4. I used a needle valve and a gauge to set this, the needle valve in on a bypass between the supply line and the return line. Race gas requires that I tweet the valve whereas pump gas needs the valve opened up a 1/4 turn to maintain the correct pressure.

[Trackrash]

Originally Posted by Jack Stands

.... with dedicated switched power. Allows me to turn off the fuel pump a bit before parking the car to lower the fuel level in the float bowls to help with percolation in the carbs.

Genius. Why didn't I think of that.