Weber conversion advice

[GDSOB]

I'm in the process replacing the MFI in my 70 2.2E with a set of Webers. Does anyone have the jetting specs for this application and know where they are available? Also, any suggestions on electric fuel pumps would be appreciated.

[Joe911]

Garth - no one has responsed so let me pass on what information I have. I have a 69S that has been converted to Webers so the jetting should be close. Venturi 32mm, main jet 130, air corrector 180, emulsion tube F3, idle jet 55. A good source of parts and information is PMO. See their advert in excellence or Pano.

[Formerly Steve Wilkinson]

I second that. Richard whatshisname at PMO is very helpful, enormously knowledgeable and a good source of whatever parts you might need.

STephan

[T Bird]

That's Richard Parr at PMO. He's also the designer and brains behind the PMO carbs.

[T Bird]

Garth

The jetting that Joe suggests sounds about right for starters on an "S." For your car (assuming it is stock), the main jets may need to be a bit smaller and/or the air correction jets a bit larger. However, the venturi size for your car is probably closer to 30mm than 32mm. The Weber formula to calculate the size of the venturi is as follows:

1) Divide the volume of one cylinder in cc's by 1000.
2) Divide the RPM where peak power is made by 1000.
3) Multiply the number derived in 1) by the number derived in 2).
4) Take the square root of the number derived in 3).
5) Multiply the number derived in 4) by 20.

For a 2.2E, the calculations are as follows:
1) 2200 cc's/6 = 367cc's; 367/1000 = .367.
2) 6200 RPM/1000 = 6.2.
3) .367 X 6.2 = 2.2754
4) Sq rt. of 2.2754 = 1.5084
5) 1.5084 X 20 = 30.168

Unless someone has some actual experience on a 2.2E here, or if Richard Parr suggests something different, 30mm is probably going to work better for you. 30mm venturis will give you a better idle than 32mm venturis since the smaller the venturi, the higher the air velocity through the carb. A higher air velocity will improve the signal received by the idle circuit, and make the circuit more responsive to adjustment. This will translate into less popping and surging and better driveability.

As for electric fuel pumps, check prior posts on this subject. My favorite is the Bosch roller cell fuel pump, PN 911.608.107.00. It has connections for delivery, return and suction and will keep fuel pressure well regulated at or below 4.2 lbs. It also should take the same electrical connector now providing current to your MFI fuel pump (at least it did so with my car) and should be the same size, so it will be a perfect retrofit.

Check the posts on fuel filters too. I use my MFI filter. There are other options available, like Racor filters.
Good luck.

[Russ]

T-Bird;
As a slight side question, how would the equation below work on setups where a two-barrel carb is fitted to a manifold feeding four cyclinders i.e. my 1438cc '68 FIAT 124 sport? What venturi sizes are suggested on the single carb?
Thank you. Russ

[BK911]

You'll also have a fuel line plumbing issue. The MFI cars have a return line and the carbed cars do not. You'll have to plug one of the taps in the fuel tank and remove a Y fitting in the supply line. You can reuse the MFI filter but you have to modify the plumbing there as well. And you arfe already aware you need a new fuel pump. The factory pump is the same size and will fit in the location of the MFI fuel pump.

Personally I would keep the MFI. If you're pump needs rebuilding the cost will be about the same as a carb conversion. But the end result will be much better.

Good luck!
BK

[si2t3m]

As T Bird mentioned there is bosch fuel pump out there for carbed Porsches (911 and 914-6). It has 3 ports so it can replace the MFI pump without having to block the return line.


Just happen to have one doing nothing on my workbench


Marc-Andre

[T Bird]

Russ
I don't know the answer to your question about a two-barrel Weber feeding 4 cylinders. I believe that the Weber formula I cited is for situations where an individual venturi is sized for a single cylinder. It doesn't appear to work correctly in situations other than that.
John

[dbanazek]

I am using a $20 checker special buzz box in my street 72 2.7 RS spec motor that I just happened to have laying around when my fuel pump quit. I have a holley "red" I think is the model in my race car. About $80 in your American performance catalogs.

[StuttgartDavid]

One question: Why are you replacing one of the finest induction systems ever sold to the public (albiet 1937 Me-109 technology) that is tailored by the factory for your application with technology that, while well executed in comparison to many other manufacturers, is the induction equivalent of a blunt instrument, is generic to your machine, and dates to the 1890s?

(I like the webers on my '68 S, but wish I had the infinitely superior MFI during track events, when the fuel level in my float bowls sloshes around like the water level in watertight compartment #3 of the Titanic, making my hardworking combustion chambers alternate between excessively rich and dangerously lean.)

[GDSOB]

I haven't checked this post for a few days and was amazed by the response. Thanks to everyone who responded. As far as my reasoning goes for using webers, this car has been either sitting or undergoing restoration since 1980. My dad started with the rust repair back then with help of the neighbor kid. I'm still cleaning guards red overspray off everything. The car has been running for the past two years, but the MFI needs a complete rebuild, linkages, butterflys, and pumps. I got a great deal on the webers, and am looking forward to driving this car soon. I haven't had the opportunity to enjoy a properly running MFI car, so we'll get the car on the road with the webers and probably rebuild the MFI when time and money permits.

Marc Andre - would you part with your fuel pump?

[rickeolis]

T-bird, we should ask ask Garth what the altitude is where he lives. I live at 5500 feet, and I need to match my jets (decreased jetting size) for the thinner air volume that I have up here, on my motorcycle it's almost as much as a 15% difference...

[StuttgartDavid]

Garth: Just a note on MFI rebuilds: While I am not an expert on MFI, I understand from my buddies that many seemingly out-of-tune MFI systems often require less work and money to bring back to life than many people believe, depending on one's intended use for the car.
The proper pump with the right space cam for your engine is the key to the entire system. Repairing the butterflies can cost big dollars, but depending on your application may or may not be necessary. I understand that while air leaks in the butterflies affect idle quality and are annoying, these smallish leaks are dwarfed by the volume of air gulped at higher rpm and really don't impact high rpm performance as long as your pump is right. Also important is having the linkage set up correctly. All 6 cylinders need the same opening at the same time under heavy throttle to avoid going lean and burning pistons, etc. If it has some slop in it, adjust what you've got so that the slack is taken out when opening under heavy throttle, 'cause this is the operating range that really counts for power and avoiding detonation.
I have several buddies who race MFI cars with worn butterflies, play in their linkages, and an irregular idle, but they swear it just doesn't matter to them for their uses and doesn't hurt their cars, so they spend their scarce racing bucks on other more pressing needs. My point? The hotrodder doesn't necessarily have to spend big bucks optimizing every facet of their MFI if you don't need to pass a smog test or idle smoothly at 600rpm. Do test the pump to make sure it's right, check the injectors for proper flow (EBS and many diesel truck shops can do this for not much $) and sync your linkage so all 6 are getting the same signal under heavy load. I understand everything else is gravy for a smooth idle and around-town driveability, but not mandatory for performance or engine safety.