PMO 46mm Carburetor Installation on 3.2L

[Gordo2]

I decided I would start up a thread dedicated to installing the PMO 46mm carburetors that I've selected for my warmed up 3.2L engine.

Background Information

Info regarding the 3.2: engine I'm building can be found here:
Gordo's 3.2L Engine Rebuild - Ready to Reassemble

Info regarding some of the fastener's I used to install the carbs & manifolds can be found here:
Studs for B&B Exhaust and PMO Manifolds


Attaching the PMO Intake Manifolds & Carburetors to the Engine

I started by placing a manifold gasket on the studs/against the head - then placed the PMO insulators on the studs - then I placed another manifold gasket on top of the insulator (the insulator is sandwiched between 2 gaskets).

The manifolds can be installed with the carburetors attached or separated. I test fit both ways and recommend installing the manifolds with the carburetors attached/fastened to the manifolds.

My vehicle is a 1983 SC which requires a vacuum source for the brake booster. The PMO manifolds that I bought have a vacuum port (threaded hole toward the center/base of the manifold) for this purpose - the vacuum ported manifold should be installed on the left side of the engine, the port over cylender #2:

Both of the gold anodized throttle linkage brackets should be mounted so they bend/face toward the rear of the vehicle / alternator assembly.



The left manifold should also have a bar sticking out of it (to mount a throttle linkage bracket) - this bar/bracket should face the front of the vehicle/flywheel end of the engine:




I purchased "K-nuts" (K-nuts: self locking nuts for motorsports | K-NUTS.com) from Henry Schmidt / Supertec to fasten the manifolds to the heads. The K-nuts have a 10mm hex head and the base circle is the diameter of a M8 nut (which doesn't fit - see 2nd link provided above). I placed a washer on each stud before I installed the nuts.

I used a 10mm socket with a universal joint and open/boxed end wrench to tighten the fasteners (I couldn't fit my torque wrench - calibrated wrist to tight enough )



Once the manifolds were installed, I placed manifold gaskets on each port and fastened the carburetors to the manifolds using M8 nuts.

With the carburetors installed, I turned to working on installing the throttle linkage.


Throttle Linkage Installation

I initially assumed I would be using the original throttle bell crank assembly/bracket that mounts to the engine, but quickly figured out it wasn't required and wouldn't fit:

Original throttle linkage assembly / bell crank laid on top of the PMO shaft with bell crank:


File size is getting large for a single post - to be continued in another post...

Gordo

[Gordo2]

Throttle Linkage Installation continued...

I also removed the studs that held the original throttle linkage base plate in place.


Throttle Linkage Cross Bar Installation

For this step, you can either loosen one of the anodized brackets from the manifold body, or you can remove one of the attached ball ends that the cross bar fits over - I loosened the 2 bolts that hold the bracket to the manifold and fit the cross bar over the ball ends of the brackets:



Once the cross bar is installed, you start to get a better feel for how the throttle linkage works.

Throttle Linkage Shaft Installation

Next I installed the adjustable throttle linkage shaft that connects bell crank (attached to the manifold) to the cross bar (shown attached in the previous picture).

Its helpful if you loosen up the throttle linkage shaft adjusters before you install them - they will need adjusted and it's difficult to break them free if they are installed.

Finally, I installed the small adjustable throttle linkage shafts to each end of the carburetors:



Once the throttle linkage was installed, I adjusted the throttle linkage shafts to provide a full range of throttle opening/closing, and confirmed that the left and right throttle linkage was adjusted to allow both to freely rest against the idle stop and provided equal throttle movement left/right.


A top view of how the installed manifolds, carburetors and linkage should look when installed (correctly I guess - this is after all, my first installation... )



I spent a bunch of time looking at pictures and researching how these things are supposed to be installed - and still got it wrong on my first "test fit".

Long winded, but I hope this helps folks looking for this kind of info in the future.

Gordo

[cgarr]

Nice! I'm watching this I really want to go this route someday. One thing if you don't want to screw around with a brake vacuum hookup on the carbs or is you don't get enough vac we used an electric vacuum pump up front just for brakes on our race car.

[KTL]

Nice writeup Gordo

Also for people not aware, there is some very helpful info on PMO's site to set them up

PMO Porsche 911 Carburetion - Installation (in the case of setting up the linkage, you want to click on the links next to the Graphic Diagram Instruction Pages)

Bulletins

[Gordo2]

Originally Posted by KTL

Nice writeup Gordo

Also for people not aware, there is some very helpful info on PMO's site to set them up

PMO Porsche 911 Carburetion - Installation (in the case of setting up the linkage, you want to click on the links next to the Graphic Diagram Instruction Pages)

Bulletins

Thanks KTL and Cgarr,

Kind of funny - I researched the crap out of carb tuning/setup and found loads of great info to include the PMO site and others way more in depth with regard to principles of Weber carb ops & tuning.

Here's some additional Weber tuning related reads (applicable to PMO's)

Weber Carbs Technical

Tuning Webers

Weber Principles

I have ~ 6 other bookmarked Pelican threads related to tuning alone (many of which KTL provided considerable input to - thanks again). I will be getting to that, once the key is turned...


Meanwhile, I hadn't really considered how the carbs & linkage mounted to the engine and simply tried to bolt them on, having found no instructions and limited references from PMO or elsewhere. I assumed it must be straightforward right?

I found that there are multiple ways you can install them incorrectly (fortunately obvious) and only one way to do it correctly. For me, it was a matter of trial and error - looking at them installed now though, it does seem obvious/straightforward.

Gordo

[Henry Schmidt]

Originally Posted by Gordo2

The bell crank linkage is mounted incorrectly. The balls should line up with the hole in the sheet metal where the linkage transitions from the transmission mounted bell crank.

[Henry Schmidt]

Without trying to be too critical of a well intentioned design, you may find your approach incapable of surviving the vibrations created by your flat six engine.

Even if the mount survives, I question whether the electronics will.

[KTL]

That's Clewett's platform. Has held up OK for our MotoDelta racecars. But i'm not going to go so far as to say the Electromotive HPX/V series or the XDi boards are indestructable.

However, the nice thing about the XDi DFU (Direct Fire Unit) coil board pictured here is that they took the electronics out and put the controls into the XDi remote ECU. The old HPX/V series boards have the electronics in the board with the coils and they've been troublesome on occasion.

[Henry Schmidt]

I just spoke to Richard as well and he confirms that as long as the electronics are separated from the board, his mounts has proven durable.

This is a prime example of theory vs observed results. It looks like it couldn't possibly work and yet, somehow it does.

[Gordo2]

Originally Posted by Henry Schmidt

The bell crank linkage is mounted incorrectly. The balls should line up with the hole in the sheet metal where the linkage transitions from the transmission mounted bell crank.

Thanks Henry - I will be installing the engine tin this weekend, will check to confirm that the bell crank ball lines up with the cutout for the throttle linkage coming from the transmission.

I've read that I will probably need to replace the bell crank mounted on the transmission with an earlier carb style bell crank to get the correct throw - otherwise I may find inconsistent pedal travel / throttle movement (touchy as you apply throttle).


PMO install and throttle linkage

The Clewett mount is pretty slick. I liked the idea that it will allow me to keep some separation between the fuel pressure reg/lines (which will be mounted to the firewall) and the coils. Wish I could claim credit for such a clean looking / functional design.

Once again, thanks for the input folks.

Gordo

[toddu]

I was able to source an early bellcrank and an early rod (from tranny through engine tin) and didn't have much tinkering to get WOT.

Now the carbs and lightweight PP and flywheel still has a learning curve with the go fast pedal ;-)

Todd

[KTL]

Another solution for getting the right throw/travel on the throttle linkage is to shorten the rod that connects to the trans bellcrank on the "upstream" side. That would be the piece that goes from the bellcrank ball socket to the boot couper. Boot coupler is the barrel-shaped piece that allows you to thread in the rod and also slip the rubber boot over it.

Shorten rod #8 in this picture. Boot coupler is #9

[Gordo2]

Here's a long overdue update...

Link to my thread on the Tech Forum discussing my approach to route / plumb the PMO carburator fuel lines:

AN-6 Fuel Line Plan for CIS to PMO Carb Conversion

Gordo

[RFP]

This is probably a dumb question, but is a PMO carb conversion possible with the engine in the car? Specifically a '87 3.2.

Thanks!

[mreid]

Yes it is. Actually, removing the current induction is the more difficult part.

[PMNorris]

Subscribed......Very helpful thread. I'm installing PMO's on an SC engine that will be fitted to me 70T. I'm a few weeks behind you. Whilst the PMO instructions are OK, the photos help a huge amount.

[Gordo2]

Originally Posted by PMNorris

Subscribed......Very helpful thread. I'm installing PMO's on an SC engine that will be fitted to me 70T. I'm a few weeks behind you. Whilst the PMO instructions are OK, the photos help a huge amount.

Few weeks behind equals well done before me at the rate I do things...

Meanwhile, as you already noticed - I started a related fuel line plumbing thread over on the Tech bullitin board.

AN-6 Fuel Line Plan for CIS to PMO Carb Conversion

Gordo

[PMNorris]

I'm catching you up Gordo. You're photos remain invaluable. One tip is to install the accelerator linkage after the carbs are fitted to the manifolds. Otherwise, tightening up some of the carb bolts is really tricky.



Paul

[toddu]

I've finally been able to drive mine around these last few weeks. You guys are gonna love it!!! I wasn't getting WOT initially and didn't realize it. Hard thing to check without a helper ;-). Anyway, adjusted the linkage a bit and I'm closer now. It REALLY gets your attention when you stand on it.

Todd

[PMNorris]

Question: Are the inlet trumpets needed inside the air filter housing like the carb on the left? I'm guessing i should keep them on, but i'd like confirmation please.



Many thanks
Paul