I say one bung

One bung to rule them all
One bung to find them
One bung to bring them all
and in the mergeness bind them


Otherwise...
Three bungs for the Elven-runners under the ports
Nine bungs for radial engines, doomed to fly

Simplify, simplify, simplify. This is my mantra.

Carbs have survived without all the fussiness for 100+ years. Having access to micro processors to analyze mixtures is fine but what is really needed is prevention of lean mixture at WOT for a sustained period of time as in during the two mile straight at LeMans.

A single AFR reading past the collector is good enough to assure adequate mixture for the engine. One per each bank of carbs is better but not necessary unless you are a racer. One per primary tube borders on geekiness seeking perfection from an archaic fuel delivery system.

I weary of perfection, as an engineer all I need is to get close enough. Leave perfection to the mathematicians.

LOL... Great memes, all...

Ok, I finally got a dual band AFR meter in and welded bungs just past the connectors and for the time being, have it hooked up to an external battery.

I let the motor warm up to 140 degrees and recorded AF at idle, 1200 rpm and 3000 rpm

In all cases, the afr was 9.2-10.3 (left bank) 10.5 to 11.5 on the right bank, so clearly running fat like a pig.....

To remind everyone, I have 60's and 165's in the car (as recommended by Richard at PMO). Can I dial this ratio down with fuel mixture and air screws or do I need new jetting?

Any comments appreciated

So I've played with mixture and air screws to the best of my ability and I have idle at just a bit rich, (13-14), but at idle i'm getting a bit of back fire out of one side. Also when I bring it up to 3,000 rpm, my ratio goes to 12.5 on pass side and 10.1 on drivers side....

Help, i'm kinda lost at this point

This tells me that your linkage is not well balanced.

This is true.

Yes the idle mixture screws opened to 2.5 turns is a starting point. You may get down to 1-1.5 turns to get a 12.5-13:1 idle. Anything leaner than that will suffer from tip in going too lean.

If left and right differ and they match at idle, with similar idle screw adjustments, then the higher power mismatch is mostly driven by linkage causing one side to open more than the other. Fiddling with the cross bar support bracket location and linkage length will change the relationship.

I did follow the online guidance last time. So I should look for movement imbalance or focus on vertical rod length at each bank?”

I usually set vertical rods the same length. Then rotate the cross bar brackets on the mounting studs/bolts to balance. Do this at the rpm where your AFR is way off.

You might have to drill the mounting holes in the brackets 1 or 2 sizes larger to get enough rotation movement to properly balance.

Carb Balance
 

When I installed my PMO's - I thought "carb balancing / synchronization" was purely associated with adjusting mixture & air corrector screws.

As I dug in, I realized its nearly entirely associated with getting the linkage on each bank of the carbs set up just right so that the carbs are responding / delivering fuel as close to the same as possible - across the left and right bank.

The bolt holes in the 2 brackets that the cross bar mounts & pivots on - are slightly enlarged. This allows you to finger tighten, and bump them a bit (forward / aft) - to fine tune adjust, and tighten once you get both banks responding equally.

Definitely one of the more tedious efforts associated with getting the carbs properly sync'd and tuned - but I think the same would be true for ITB's that us the same linkage design. Once set - I avoid removing / adjusting as much as possible (once set - you normally don't need to adjust unless you remove the carbs / linkage).

BTW - I used 2 synchrometers (left / right) to setup mine, but can be done with one (moved across the banks), or via your dual wideband. The synchrometers measure air flow - which ultimately determines how much air/fuel your carbs will pull in and the resulting air/fuel measurement you will read on a wideband (i.e. rich or lean).

Good luck,

Well Interestingly enough, I have not had a chance to play with it today (damn work gets in the way all the time) but I did notice when I was cleaning the carbs that the PO hogged out the holes for the brackets where the 2 bolts on either side of the cross rod bolt into the manifolds... Clearly in retrospect they could be off.... I'll dig into it in the am

Gordo, I too bought 2 sync tools to hopefully help speed up the process

So, is there are guideline or basic position/set up on rod lengths and positioning, and or angles to start at? Mine look to be at an angle and I'm not sure they should be...?

https://imgur.com/vYrDFGQ

https://imgur.com/zxToZAe

https://imgur.com/HGpWjM3

https://imgur.com/F2rZxkX

https://imgur.com/F2rZxkX
https://imgur.com/zxToZAe
https://imgur.com/HGpWjM3
https://imgur.com/F2rZxkX

Check the PMO website links for Linkage Geometry and Linkage:

https://www.pmocarb.com/installation.htm

Best info I was able to find to assist with & visualize correct adjustment - but the process still took a good deal of adjusting various linkage connections to get it correct.

Good luck,

Thanks Gordo... So I spent some time working on linkage Geometry today by a, insuring the throttle rods are the same length and mine both measure 82.68mm.. So I know both rods are the same.

Then I set the W & X angle (as outlined here; https://www.pmocarb.com/Images/Instructions-4.gif) and although the bottom of my rod is further out than the upper as seen in the pic (maybe something being 3.6 and 50pmo's vs older, smaller engines), my W & X ratio is both are set 24.5mm in (upper ball is more forward then the lower ball).

I am having a difficult time adjusting the Y to Z ratio ratio as seen in the above diagram. Ideally the cross bar needs to go towards the passenger side some 3-4 mm from where the rod rests, but there is a about another 3-4mm play of the cross rod in a neutral position ( space in the ball rod ends against the sockets is sloppy)

Additionally I don't see any adjuster nut on the left side of the cross rod... (could be missing it I guess),

Cross rod is 15 1/2 -9/16 across, so I don't think that is bent

So my questions are:

1. how important is the Y & Z measurement if W & X are close

2. being there is not adjuster nut on the drivers side of the cross bar, do I need to disassemble and put one it?

3. If I do put an adjuster nut in and move the cross bar over towards the passenger side, how much tension can there or should there be on the cross bar before its too much?

I did not run the car, as I guess if you all say the Y/Z measurement is important....

Thanks for your continuing advice and I hope this thread helps others in the future..

The pic doesn't show how far off the y?z measurement is but I need to more the rod to the left about 3-4 mm

https://imgur.com/mIM5Tqn