911 3.2 Carrera on Zenith carbs air leak advice help Please!

[greg356a]

Ok, so we are completely out of ideas and inspiration as to what the cure is, really could do with help or shared experiences.
I have a 1986 3.2 Carrera engine running on Zenith tin 40’s. The problem is with 1, 2 , 3 bank not running which seems to be caused by air leak/s.
Issue;
Not running on No 1 and 3 cylinders
Prior to reaming out carb for oversized shafts 8.2 mm was running on 1 & 3 but not 2
Spray easy start around manifolds, carbs on 1 & 2 no change. Spray near the front on No 1 slight engine note change. Much worse on all three especially No 2 prior to changing to oversized shafts.
Balance on airflow meter high on scale left side fine right side bank.
Remove HT leads on 2 & 3 no change to engine, but remove no 1 and engine dies as you would expect
Condition;
New HT leads, distributor etc
No know problems with the engine, no smoke, valves reset etc
Carbs rebuilt including adding oversize 8.2 mm butterfly shafts, no play in bearings
Butterfly to carb body sealing is not absolutely perfect, holding carb up to the light there is a very faint line of light around each of the three chambers. I have adjusted to make fit best as possible
Manifolds no obvious cracks, pin holes etc
Gaskets were new but carb has been on and off several times. Gasket cover all the previous induction holes and have a spacer.
Accelerator jets function correctly.

So its running fine on 4,5,6 and firing on 1 but not 2 & 3 but air leak seems to be at No 1 but cant find it

Really struggling, and would appreciate any help or advice

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[911hillclimber]

Not sure if this will help, maybe it will.
I have a 3.2 in my race car with PMO carbs and manifolds.

The 3.2 heads have a small cut away to allow the injectors a direct target to the inlet valve.
If you do not have the correct gaskets you can get a hair line gap exposed from the edge of the injector cut away and the outside world allowing air to that cylinder to be greater than the others and give all manner of running issues.

I had this issue some years ago and discovered it by spraying carb cleaner,brake cleaner to the various head, gasket, insulator, gasket, carb base interfaces.
The tone of the running engine would change pronounced when the spray closed the gap I describe for about 3 to 5 seconds as the engine ingested the spray with the excess air.

Another clue was the big difference to the various needle positions across the 6 cylinders, the cylinder s ( I had 2 problem ones) would have very different mixture positions to the other 4 and the prob cylinders were difficult to match the balance of air flow across each cylinder.

As I say, maybe all a red herring, but I made my own gaskets in the end so to fully cover the injector cut away and everything chimed in perfectly.
That was 4 years ago, all is still good.
Good luck, you have a smashing car.

[greg356a]

Appreciate the feedback, but we have already changed the gaskets so as to cover the injection holes. I found a set in the USA with plastic spacers as well to help avoid the heat issues. Will take another look and see if I missed anything, but the right bank is perfect.

Starting to think seriously about new carbs and maybe manifolds but they are not cheap and not sure if that it the answer.

What size and settings are your PMO's and did you find them in the UK?

thanks again

[911hillclimber]

My PMO carbs are huge 50mm chokes so too big for th 3.2 wher 46mm are ideal.
No idea of the jet sizes, but PMO will be able to tell you.
My carbs came from a rally guy in Wales years ago, exchanged some 40's Weber for them and a fist of pound notes...
They are fabulous, great design and full of nice ideas, the spindle shafts run in sealed ball races etc.

[greg356a]

Thanks 911hillclimber as you have said "never give up"

So working on the assumption that the worn throttle shafts have caused the throttle valve seats to wear I have ordered new throttle valves and will spend time fitting so as to get a seal between the valve and the carb chamber/ body of less than 2 thou. We think they are about 6 thou. Best guess.

Also ordered two more sets of gaskets from PartsKlassiK in the USA, These are the same as already fitted and designed to cut out the injection hole. Just thinking that the manifolds have been on and off so many times that I might have crushed the gaskets.

PMO's do look very impressive and 46mm should be a good starting point, just deciding which arm and leg to cut off!

If these mods don't work might have to suck it up and buy a set.

[911hillclimber]

Dare I say a set of 40mm webers would make for a very torquey engine?

[greg356a]

Ok, so still struggling with the Zeniths. Passed the point of no return!

Stripped them out again to change the pump jet O rings to the correct size (3mm id and 2mm section from the Pelican) Having done that the engine wont start. I guess fuel is being forced around the O ring rather than the through the jet. Having left the carbs standing on the bench for a couple of days I noticed the fuel in the bowls is full of dirt/ debris. I guess 50 years of crap just cant be cleaned away despite repeated attempts.

Ready to buy a set of 46mm PMO's. I am using a 123/tune programmable distributor with vacuum advance but I understand that PMO's don't have a vacuum advance option? so how do I over come the problem?

Any help advice gratefully received

[Ian Comerford]

Have you considered asking PMO?

[greg356a]

Richard Parr only seems to take questions via fax, who has a fax machine these days? Still stops hundreds of emails

I have also asked the question via a distributor here in the UK.

Cheers

[MikeB]

If there is dirt in the fuel bowls then the chances are there are bits in the fuel passages inside the carb and the jets. Have you checked that the accelerator jets are working and spraying fuel into the carb barrels when you press the throttle? Have you tried squirting fuel directly into the carb intakes to see if the engine picks up, if so this would indicate that your idle circuit jets are blocked. Do you have a fuel filter in-line before the carbs, could the muck in the fuel bowls be coming from the tank/ pipe work?

[greg356a]

From previously running the only thing I changed was the O rings around the pump jets and now wont even fire. Certainly the muck is an issue, yes fitted fuel filter, new fuel lines etc, etc. Carbs have been cleaned and cleaned. It must be some muck in the hidden paths of the carb.
One of the pump jets was blocked again. But one blocked jet would not normally stop the other 5 from firing. I should have checked the fuel pumping via the jets before I stripped them off again but I was confident over size O rings would be the answer, unfortunately these have not arrived yet.

[greg356a]

Morning,

Any experience of running PMO's with or without a distributor with vacuum advance?

[MikeB]

Yes, have run PMOs on a 2.2 engine, great carbs and great service from Richard Parr. Basically an improved design on the Weber, uses the same jets etc. That was on a car without Vac Advance. Currently run by SC on Webers with the 76-78 non vac advance distributor which is said to be the one to use

[greg356a]

Hi MikeB,

How did you communicate with Richard via fax?

[MikeB]

I may have an email addy, I’ll check