Tuning PMO Carbs with a difference?

[911hillclimber]

Looks like the hill climb season will kick-off as planned, first event I hope will be in late April with the 3.2 engine Lola.

The stock 3.2 flat 6 in the car has PMO carbs and was originally set-up by Bob Watson about 9 years ago...

I have tweaked the carbs over time using a simple synchro meter to get the choke balances all the same and that has worked well, but is there more, and this is the point of this thread.

I don't want to fuss with rolling roads, I'm not good enough at driving this thing to be splitting hairs, just want a good weekend on the hills.

The engine last year was 'popping' more than is normal, so will check for air leaks on the induction/exhaust side before checking balance, BUT, the ex manifolds have ports for a lambda sensor which Bob used to set the mixture. The senders are just after where the (custom made) individual pipes merge to 1 larger tube before the large silencers. The exhaust pipes are NOT merged, each bank goes 3 into one into a silencer.

Is there anything to be gained to have sensors in these ports for checking mixture, and if so, is there any kit any can recommend that would do this job (and be worth it?).

The ignition is a simple coil and contact breaker, absolutely nothing special.

[MikeB]

Graham

Having sensors will only be good if you can take it somewhere you can drive it and then read the data or watch a gauge, if you are just doing it with the car running on the idle circuit, i.e. up to circa 2200 rpm it won't tell you anything about the main fuel/air circuit which you will be on when competing, so you need to go to either a circuit of a rolling road.

For air leaks start spraying carb cleaner round the inlet manifold to see if it detects any leaks

[911hillclimber]

Now, that is a good point Mike!
Sorry to not have thought about that, but I could do this on the hill and at least gather some info.
Bob said he set it on the rich side as he knew from my previous hill working most of the time the engine is WOT as you know.
Is there a simple way to log the mixture under load using these sensors?

[Jonny Hart]

Like I said before, stick a CDI on it. It will be night and day difference over kettering.

[mycar]

As above, addressing the ignition, whether crank fire, CDi or 123 distributor, will revolutionise your experience.

[rhd racer]

Hi Graham

Despite you downplaying effort vs ability, I would personally take the advice re the ignition and then get it booked onto a trusted rolling road for a re-jet and set up to optimise what you have. You might spend £200-£300 but you will get that back in spades; yes more power, but also more torque, better starting, assurance that you are not lean in the wrong places etc etc

My experience was the same as yours, Bob set it up and it was utterly perfect and the best it could be (I remember he ran the tiniest drill bit through a jet on mine because he didn’t have the right one in stock). But the fact is, every time you take off a carb to do a job you move away from the optimum, and it’s not quite as crisp or smooth or oomphy (if that’s a word) as it was before.

I wouldn’t hesitate, you have time, and a trailer, so get it done once and then leave for the next 9 years!

Look forward to seeing you at Loton in June,

Cheers
Wayne

[911hillclimber]

Thanks to all for the advice.
Wayne, guess you are right, I'm not sure how much the engine has 'drifted' from Bob's settings.
Bob spent AGES on the car, the bill was enormous, and I was disappointed by 247 bhp, but the carbs are far too big for the capacity.

I am loath to spend a 4 figure sum on this car, I am nowhere near the top of the class (you know too well who I'm up against).
Most tuners I know will scratch their heads at the PMO carbs and may well do a worse job due to unfamiliarity, I had the same many years ago with the Webers originally on this engine (that were too small!).

I think I will go through the routine of balance and see how it is next week if the weather is good.

I'm hoping to do the first Prescott at the end of April, first round in the Midland Championship, going to feel SOOOOO rusty!

[hot66]

I have Daytona sensors afr dual band on my car .. lambda in each exhausts bank. It also has data logging so can be read afterwards against rpm etc ( Ive not done this as my laptop is a Mac and it’s not compatible plus I’ve lost my rpm feed for some reason ) .

[911hillclimber]

Thank you all esp the detailed pm I've received on the subject.

Today a change of plans, so the engine will get a simple DIY leak test and a check on air passage balance on all chokes.
Funds going 'elsewhere'!

[PeterK]

Thanks to all for the advice.
Wayne, guess you are right, I'm not sure how much the engine has 'drifted' from Bob's settings.
Bob spent AGES on the car, the bill was enormous, and I was disappointed by 247 bhp, but the carbs are far too big for the capacity.

If the carbs are too big, then you’re wasting torque, which I guess could be useful in hill climbing.

[911hillclimber]

You sound like Bob Watson!

I had a big problem with this engine and the carbs that came with it and after a lot of hassle traded some 3/4 decent Weber 40's for these 50mm PMO's which were near new.
Ideal carb size would be 46mm.
I think the chokes are 38mm (it was a long time ago) and bob had some probs with them, but iirc the engine gave 224 LbFt / 247 bhp at the flywheel.

Bob threw the Aldon electronic ignition out and fitted FoMoCo coil and simple early 911 ignition parts which the engine still has. 'Morris Minor' technology.
In all truth I may be coming to the end of my tenure with this car and even the hill climb sport after 30 years 'competing' so reluctant to invest any/much more into the car.
It is just an 'oldman' thing, comes to us all eventually.
Can see myself hill climbing the Boxster though, very simple way to do hillclimbing, just as I started with the 911!

Feel very much at a crossroad.

[Jonny Hart]

As per your last thread on updating, you are losing spark energy progressively with RPM with your Kettering ignition, especially with those giant carbs.

It would not surprise me if you saw an uplift of 20HP and the throttle response will be way better with a CDI system. It’s probably the biggest bang for buck out of any of the options you are considering.

I’m sure Angus will chime in on his recent experience putting one of our boxes on a 68T (only E and S got CDI). Transformation was the word he used.

[911hillclimber]

But it will need a rolling road session to map it?
The distributor is a 2.7 RS spec (I've been told) but I do know who built this unusual engine so can check.
Can the CDI me matched to the dist.
How do you install this unit please.
Graham.

[Jonny Hart]

But it will need a rolling road session to map it?
The distributor is a 2.7 RS spec (I've been told) but I do know who built this unusual engine so can check.
Can the CDI me matched to the dist.
How do you install this unit please.
Graham.

You can map it but you will still see a benefit without, purely down to spark energy.

It will work with your distributor, you would just need to make up a wiring loom as CDI wiring is a little different (there is no 12V connection to the coil). You would need a proper CDI coil also (Bosch black).

[911hillclimber]

Thank you for the details, time to think if this cost will give a return on the times up the hill.